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1 Introspection Datasette includes some pages and JSON API endpoints for introspecting the current instance. These can be used to understand some of the internals of Datasette and to see how a particular instance has been configured. Each of these pages can be viewed in your browser. Add .json to the URL to get back the contents as JSON. 8  
2 /-/metadata Shows the contents of the metadata.json file that was passed to datasette serve , if any. Metadata example : { "license": "CC Attribution 4.0 License", "license_url": "http://creativecommons.org/licenses/by/4.0/", "source": "fivethirtyeight/data on GitHub", "source_url": "https://github.com/fivethirtyeight/data", "title": "Five Thirty Eight", "databases": { } } 8  
3 /-/versions Shows the version of Datasette, Python and SQLite. Versions example : { "datasette": { "version": "0.21" }, "python": { "full": "3.6.5 (default, May 5 2018, 03:07:21) \n[GCC 6.3.0 20170516]", "version": "3.6.5" }, "sqlite": { "extensions": { "json1": null }, "fts_versions": [ "FTS5", "FTS4", "FTS3" ], "compile_options": [ "COMPILER=gcc-6.3.0 20170516", "ENABLE_FTS3", "ENABLE_FTS4", "ENABLE_FTS5", "ENABLE_JSON1", "ENABLE_RTREE", "THREADSAFE=1" ], "version": "3.16.2" } } 8  
4 /-/plugins Shows a list of currently installed plugins and their versions. Plugins example : [ { "name": "datasette_cluster_map", "static": true, "templates": false, "version": "0.10", "hooks": ["extra_css_urls", "extra_js_urls", "extra_body_script"] } ] Add ?all=1 to include details of the default plugins baked into Datasette. 8  
5 /-/settings Shows the Settings for this instance of Datasette. Settings example : { "default_facet_size": 30, "default_page_size": 100, "facet_suggest_time_limit_ms": 50, "facet_time_limit_ms": 1000, "max_returned_rows": 1000, "sql_time_limit_ms": 1000 } 8  
6 /-/databases Shows currently attached databases. Databases example : [ { "hash": null, "is_memory": false, "is_mutable": true, "name": "fixtures", "path": "fixtures.db", "size": 225280 } ] 8  
7 /-/threads Shows details of threads and asyncio tasks. Threads example : { "num_threads": 2, "threads": [ { "daemon": false, "ident": 4759197120, "name": "MainThread" }, { "daemon": true, "ident": 123145319682048, "name": "Thread-1" }, ], "num_tasks": 3, "tasks": [ "<Task pending coro=<RequestResponseCycle.run_asgi() running at uvicorn/protocols/http/httptools_impl.py:385> cb=[set.discard()]>", "<Task pending coro=<Server.serve() running at uvicorn/main.py:361> wait_for=<Future pending cb=[<TaskWakeupMethWrapper object at 0x10365c3d0>()]> cb=[run_until_complete.<locals>.<lambda>()]>", "<Task pending coro=<LifespanOn.main() running at uvicorn/lifespan/on.py:48> wait_for=<Future pending cb=[<TaskWakeupMethWrapper object at 0x10364f050>()]>>" ] } 8  
8 /-/actor Shows the currently authenticated actor. Useful for debugging Datasette authentication plugins. { "actor": { "id": 1, "username": "some-user" } } 8  
9 /-/messages The debug tool at /-/messages can be used to set flash messages to try out that feature. See .add_message(request, message, message_type=datasette.INFO) for details of this feature. 8  
10 The Datasette Ecosystem Datasette sits at the center of a growing ecosystem of open source tools aimed at making it as easy as possible to gather, analyze and publish interesting data. These tools are divided into two main groups: tools for building SQLite databases (for use with Datasette) and plugins that extend Datasette's functionality. The Datasette project website includes a directory of plugins and a directory of tools: Plugins directory on datasette.io Tools directory on datasette.io 8  
11 sqlite-utils sqlite-utils is a key building block for the wider Datasette ecosystem. It provides a collection of utilities for manipulating SQLite databases, both as a Python library and a command-line utility. Features include: Insert data into a SQLite database from JSON, CSV or TSV, automatically creating tables with the correct schema or altering existing tables to add missing columns. Configure tables for use with SQLite full-text search, including creating triggers needed to keep the search index up-to-date. Modify tables in ways that are not supported by SQLite's default ALTER TABLE syntax - for example changing the types of columns or selecting a new primary key for a table. Adding foreign keys to existing database tables. Extracting columns of data into a separate lookup table. 8  
12 Dogsheep Dogsheep is a collection of tools for personal analytics using SQLite and Datasette. The project provides tools like github-to-sqlite and twitter-to-sqlite that can import data from different sources in order to create a personal data warehouse. Personal Data Warehouses: Reclaiming Your Data is a talk that explains Dogsheep and demonstrates it in action. 8  
13 Testing plugins We recommend using pytest to write automated tests for your plugins. If you use the template described in Starting an installable plugin using cookiecutter your plugin will start with a single test in your tests/ directory that looks like this: from datasette.app import Datasette import pytest @pytest.mark.asyncio async def test_plugin_is_installed(): datasette = Datasette([], memory=True) response = await datasette.client.get("/-/plugins.json") assert response.status_code == 200 installed_plugins = {p["name"] for p in response.json()} assert "datasette-plugin-template-demo" in installed_plugins This test uses the datasette.client object to exercise a test instance of Datasette. datasette.client is a wrapper around the HTTPX Python library which can imitate HTTP requests using ASGI. This is the recommended way to write tests against a Datasette instance. This test also uses the pytest-asyncio package to add support for async def test functions running under pytest. You can install these packages like so: pip install pytest pytest-asyncio If you are building an installable package you can add them as test dependencies to your setup.py module like this: setup( name="datasette-my-plugin", # ... extras_require={ "test": ["pytest", "pytest-asyncio"] }, tests_require=["datasette-my-plugin[test]"], ) You can then install the test dependencies like so: pip install -e '.[test]' Then run the tests using pytest like so: pytest 8  
14 Using pdb for errors thrown inside Datasette If an exception occurs within Datasette itself during a test, the response returned to your plugin will have a response.status_code value of 500. You can add pdb=True to the Datasette constructor to drop into a Python debugger session inside your test run instead of getting back a 500 response code. This is equivalent to running the datasette command-line tool with the --pdb option. Here's what that looks like in a test function: def test_that_opens_the_debugger_or_errors(): ds = Datasette([db_path], pdb=True) response = await ds.client.get("/") If you use this pattern you will need to run pytest with the -s option to avoid capturing stdin/stdout in order to interact with the debugger prompt. 8  
15 Using pytest fixtures Pytest fixtures can be used to create initial testable objects which can then be used by multiple tests. A common pattern for Datasette plugins is to create a fixture which sets up a temporary test database and wraps it in a Datasette instance. Here's an example that uses the sqlite-utils library to populate a temporary test database. It also sets the title of that table using a simulated metadata.json configuration: from datasette.app import Datasette import pytest import sqlite_utils @pytest.fixture(scope="session") def datasette(tmp_path_factory): db_directory = tmp_path_factory.mktemp("dbs") db_path = db_directory / "test.db" db = sqlite_utils.Database(db_path) db["dogs"].insert_all([ {"id": 1, "name": "Cleo", "age": 5}, {"id": 2, "name": "Pancakes", "age": 4} ], pk="id") datasette = Datasette( [db_path], metadata={ "databases": { "test": { "tables": { "dogs": { "title": "Some dogs" } } } } } ) return datasette @pytest.mark.asyncio async def test_example_table_json(datasette): response = await datasette.client.get("/test/dogs.json?_shape=array") assert response.status_code == 200 assert response.json() == [ {"id": 1, "name": "Cleo", "age": 5}, {"id": 2, "name": "Pancakes", "age": 4}, ] @pytest.mark.asyncio async def test_example_table_html(datasette): response = await datasette.client.get("/test/dogs") assert ">Some dogs</h1>" in response.text Here the datasette() function defines the fixture, which is than automatically passed to the two test functions based on pytest automatically matching their datasette function parameters. The @pytest.fixture(scope="session") line here ensures the fixture is reused for the full pytest execution session. This… 8  
16 Testing outbound HTTP calls with pytest-httpx If your plugin makes outbound HTTP calls - for example datasette-auth-github or datasette-import-table - you may need to mock those HTTP requests in your tests. The pytest-httpx package is a useful library for mocking calls. It can be tricky to use with Datasette though since it mocks all HTTPX requests, and Datasette's own testing mechanism uses HTTPX internally. To avoid breaking your tests, you can return ["localhost"] from the non_mocked_hosts() fixture. As an example, here's a very simple plugin which executes an HTTP response and returns the resulting content: from datasette import hookimpl from datasette.utils.asgi import Response import httpx @hookimpl def register_routes(): return [ (r"^/-/fetch-url$", fetch_url), ] async def fetch_url(datasette, request): if request.method == "GET": return Response.html( """ <form action="/-/fetch-url" method="post"> <input type="hidden" name="csrftoken" value="{}"> <input name="url"><input type="submit"> </form>""".format( request.scope["csrftoken"]() ) ) vars = await request.post_vars() url = vars["url"] return Response.text(httpx.get(url).text) Here's a test for that plugin that mocks the HTTPX outbound request: from datasette.app import Datasette import pytest @pytest.fixture def non_mocked_hosts(): # This ensures httpx-mock will not affect Datasette's own # httpx calls made in the tests by datasette.client: return ["localhost"] async def test_outbound_http_call(httpx_mock): httpx_mock.add_response( url='https://www.example.com/', data='Hello world', ) datasette = Datasette([], memory=True) response = await datasette.client.post("/-/fetch-url", data={ "url": "https://www.example.com/" }) assert response.text == "Hello world" outbound_request = httpx_mock.get_request() asse… 8  
17 Writing plugins You can write one-off plugins that apply to just one Datasette instance, or you can write plugins which can be installed using pip and can be shipped to the Python Package Index ( PyPI ) for other people to install. Want to start by looking at an example? The Datasette plugins directory lists more than 50 open source plugins with code you can explore. The plugin hooks page includes links to example plugins for each of the documented hooks. 8  
18 Writing one-off plugins The quickest way to start writing a plugin is to create a my_plugin.py file and drop it into your plugins/ directory. Here is an example plugin, which adds a new custom SQL function called hello_world() which takes no arguments and returns the string Hello world! . from datasette import hookimpl @hookimpl def prepare_connection(conn): conn.create_function('hello_world', 0, lambda: 'Hello world!') If you save this in plugins/my_plugin.py you can then start Datasette like this: datasette serve mydb.db --plugins-dir=plugins/ Now you can navigate to http://localhost:8001/mydb and run this SQL: select hello_world(); To see the output of your plugin. 8  
19 Starting an installable plugin using cookiecutter Plugins that can be installed should be written as Python packages using a setup.py file. The quickest way to start writing one an installable plugin is to use the datasette-plugin cookiecutter template. This creates a new plugin structure for you complete with an example test and GitHub Actions workflows for testing and publishing your plugin. Install cookiecutter and then run this command to start building a plugin using the template: cookiecutter gh:simonw/datasette-plugin Read a cookiecutter template for writing Datasette plugins for more information about this template. 8  
20 Packaging a plugin Plugins can be packaged using Python setuptools. You can see an example of a packaged plugin at https://github.com/simonw/datasette-plugin-demos The example consists of two files: a setup.py file that defines the plugin: from setuptools import setup VERSION = '0.1' setup( name='datasette-plugin-demos', description='Examples of plugins for Datasette', author='Simon Willison', url='https://github.com/simonw/datasette-plugin-demos', license='Apache License, Version 2.0', version=VERSION, py_modules=['datasette_plugin_demos'], entry_points={ 'datasette': [ 'plugin_demos = datasette_plugin_demos' ] }, install_requires=['datasette'] ) And a Python module file, datasette_plugin_demos.py , that implements the plugin: from datasette import hookimpl import random @hookimpl def prepare_jinja2_environment(env): env.filters['uppercase'] = lambda u: u.upper() @hookimpl def prepare_connection(conn): conn.create_function('random_integer', 2, random.randint) Having built a plugin in this way you can turn it into an installable package using the following command: python3 setup.py sdist This will create a .tar.gz file in the dist/ directory. You can then install your new plugin into a Datasette virtual environment or Docker container using pip : pip install datasette-plugin-demos-0.1.tar.gz To learn how to upload your plugin to PyPI for use by other people, read the PyPA guide to Packaging and distributing projects . 8  
21 Static assets If your plugin has a static/ directory, Datasette will automatically configure itself to serve those static assets from the following path: /-/static-plugins/NAME_OF_PLUGIN_PACKAGE/yourfile.js Use the datasette.urls.static_plugins(plugin_name, path) method to generate URLs to that asset that take the base_url setting into account, see datasette.urls . To bundle the static assets for a plugin in the package that you publish to PyPI, add the following to the plugin's setup.py : package_data={ 'datasette_plugin_name': [ 'static/plugin.js', ], }, Where datasette_plugin_name is the name of the plugin package (note that it uses underscores, not hyphens) and static/plugin.js is the path within that package to the static file. datasette-cluster-map is a useful example of a plugin that includes packaged static assets in this way. 8  
22 Custom templates If your plugin has a templates/ directory, Datasette will attempt to load templates from that directory before it uses its own default templates. The priority order for template loading is: templates from the --template-dir argument, if specified templates from the templates/ directory in any installed plugins default templates that ship with Datasette See Custom pages and templates for more details on how to write custom templates, including which filenames to use to customize which parts of the Datasette UI. Templates should be bundled for distribution using the same package_data mechanism in setup.py described for static assets above, for example: package_data={ 'datasette_plugin_name': [ 'templates/my_template.html', ], }, You can also use wildcards here such as templates/*.html . See datasette-edit-schema for an example of this pattern. 8  
23 Writing plugins that accept configuration When you are writing plugins, you can access plugin configuration like this using the datasette plugin_config() method. If you know you need plugin configuration for a specific table, you can access it like this: plugin_config = datasette.plugin_config( "datasette-cluster-map", database="sf-trees", table="Street_Tree_List" ) This will return the {"latitude_column": "lat", "longitude_column": "lng"} in the above example. If it cannot find the requested configuration at the table layer, it will fall back to the database layer and then the root layer. For example, a user may have set the plugin configuration option like so: { "databases: { "sf-trees": { "plugins": { "datasette-cluster-map": { "latitude_column": "xlat", "longitude_column": "xlng" } } } } } In this case, the above code would return that configuration for ANY table within the sf-trees database. The plugin configuration could also be set at the top level of metadata.json : { "title": "This is the top-level title in metadata.json", "plugins": { "datasette-cluster-map": { "latitude_column": "xlat", "longitude_column": "xlng" } } } Now that datasette-cluster-map plugin configuration will apply to every table in every database. 8  
24 Designing URLs for your plugin You can register new URL routes within Datasette using the register_routes() plugin hook. Datasette's default URLs include these: /dbname - database page /dbname/tablename - table page /dbname/tablename/pk - row page See Pages and API endpoints and Introspection for more default URL routes. To avoid accidentally conflicting with a database file that may be loaded into Datasette, plugins should register URLs using a /-/ prefix. For example, if your plugin adds a new interface for uploading Excel files you might register a URL route like this one: /-/upload-excel Try to avoid registering URLs that clash with other plugins that your users might have installed. There is no central repository of reserved URL paths (yet) but you can review existing plugins by browsing the datasette-plugin topic on GitHub. If your plugin includes functionality that relates to a specific database you could also register a URL route like this: /dbname/-/upload-excel Or for a specific table like this: /dbname/tablename/-/modify-table-schema Note that a row could have a primary key of - and this URL scheme will still work, because Datasette row pages do not ever have a trailing slash followed by additional path components. 8  
25 Building URLs within plugins Plugins that define their own custom user interface elements may need to link to other pages within Datasette. This can be a bit tricky if the Datasette instance is using the base_url configuration setting to run behind a proxy, since that can cause Datasette's URLs to include an additional prefix. The datasette.urls object provides internal methods for correctly generating URLs to different pages within Datasette, taking any base_url configuration into account. This object is exposed in templates as the urls variable, which can be used like this: Back to the <a href="{{ urls.instance() }}">Homepage</a> See datasette.urls for full details on this object. 8  
26 JSON API Datasette provides a JSON API for your SQLite databases. Anything you can do through the Datasette user interface can also be accessed as JSON via the API. To access the API for a page, either click on the .json link on that page or edit the URL and add a .json extension to it. If you started Datasette with the --cors option, each JSON endpoint will be served with the following additional HTTP header: Access-Control-Allow-Origin: * This means JavaScript running on any domain will be able to make cross-origin requests to fetch the data. If you start Datasette without the --cors option only JavaScript running on the same domain as Datasette will be able to access the API. 8  
27 Different shapes The default JSON representation of data from a SQLite table or custom query looks like this: { "database": "sf-trees", "table": "qSpecies", "columns": [ "id", "value" ], "rows": [ [ 1, "Myoporum laetum :: Myoporum" ], [ 2, "Metrosideros excelsa :: New Zealand Xmas Tree" ], [ 3, "Pinus radiata :: Monterey Pine" ] ], "truncated": false, "next": "100", "next_url": "http://127.0.0.1:8001/sf-trees-02c8ef1/qSpecies.json?_next=100", "query_ms": 1.9571781158447266 } The columns key lists the columns that are being returned, and the rows key then returns a list of lists, each one representing a row. The order of the values in each row corresponds to the columns. The _shape parameter can be used to access alternative formats for the rows key which may be more convenient for your application. There are three options: ?_shape=arrays - "rows" is the default option, shown above ?_shape=objects - "rows" is a list of JSON key/value objects ?_shape=array - an JSON array of objects ?_shape=array&_nl=on - a newline-separated list of JSON objects ?_shape=arrayfirst - a flat JSON array containing just the first value from each row ?_shape=object - a JSON object keyed using the primary keys of the rows _shape=objects looks like this: { "database": "sf-trees", ... "rows": [ { "id": 1, … 8  
28 Pagination The default JSON representation includes a "next_url" key which can be used to access the next page of results. If that key is null or missing then it means you have reached the final page of results. Other representations include pagination information in the link HTTP header. That header will look something like this: link: <https://latest.datasette.io/fixtures/sortable.json?_next=d%2Cv>; rel="next" Here is an example Python function built using requests that returns a list of all of the paginated items from one of these API endpoints: def paginate(url): items = [] while url: response = requests.get(url) try: url = response.links.get("next").get("url") except AttributeError: url = None items.extend(response.json()) return items 8  
29 Special JSON arguments Every Datasette endpoint that can return JSON also accepts the following query string arguments: ?_shape=SHAPE The shape of the JSON to return, documented above. ?_nl=on When used with ?_shape=array produces newline-delimited JSON objects. ?_json=COLUMN1&_json=COLUMN2 If any of your SQLite columns contain JSON values, you can use one or more _json= parameters to request that those columns be returned as regular JSON. Without this argument those columns will be returned as JSON objects that have been double-encoded into a JSON string value. Compare this query without the argument to this query using the argument ?_json_infinity=on If your data contains infinity or -infinity values, Datasette will replace them with None when returning them as JSON. If you pass _json_infinity=1 Datasette will instead return them as Infinity or -Infinity which is invalid JSON but can be processed by some custom JSON parsers. ?_timelimit=MS Sets a custom time limit for the query in ms. You can use this for optimistic queries where you would like Datasette to give up if the query takes too long, for example if you want to implement autocomplete search but only… 8  
30 Table arguments The Datasette table view takes a number of special query string arguments. 8  
31 Column filter arguments You can filter the data returned by the table based on column values using a query string argument. ?column__exact=value or ?_column=value Returns rows where the specified column exactly matches the value. ?column__not=value Returns rows where the column does not match the value. ?column__contains=value Rows where the string column contains the specified value ( column like "%value%" in SQL). ?column__endswith=value Rows where the string column ends with the specified value ( column like "%value" in SQL). ?column__startswith=value Rows where the string column starts with the specified value ( column like "value%" in SQL). ?column__gt=value Rows which are greater than the specified value. ?column__gte=value Rows which are greater than or equal to the specified value. ?column__lt=value Rows which are less than the specified value. … 8  
32 Special table arguments ?_col=COLUMN1&_col=COLUMN2 List specific columns to display. These will be shown along with any primary keys. ?_nocol=COLUMN1&_nocol=COLUMN2 List specific columns to hide - any column not listed will be displayed. Primary keys cannot be hidden. ?_labels=on/off Expand foreign key references for every possible column. See below. ?_label=COLUMN1&_label=COLUMN2 Expand foreign key references for one or more specified columns. ?_size=1000 or ?_size=max Sets a custom page size. This cannot exceed the max_returned_rows limit passed to datasette serve . Use max to get max_returned_rows . ?_sort=COLUMN Sorts the results by the specified column. ?_sort_desc=COLUMN Sorts the results by the specified column in descending order. ?_search=keywords For SQLite tables that have been configured for full-text search executes a search … 8  
33 Expanding foreign key references Datasette can detect foreign key relationships and resolve those references into labels. The HTML interface does this by default for every detected foreign key column - you can turn that off using ?_labels=off . You can request foreign keys be expanded in JSON using the _labels=on or _label=COLUMN special query string parameters. Here's what an expanded row looks like: [ { "rowid": 1, "TreeID": 141565, "qLegalStatus": { "value": 1, "label": "Permitted Site" }, "qSpecies": { "value": 1, "label": "Myoporum laetum :: Myoporum" }, "qAddress": "501X Baker St", "SiteOrder": 1 } ] The column in the foreign key table that is used for the label can be specified in metadata.json - see Specifying the label column for a table . 8  
34 Datasette An open source multi-tool for exploring and publishing data Datasette is a tool for exploring and publishing data. It helps people take data of any shape or size and publish that as an interactive, explorable website and accompanying API. Datasette is aimed at data journalists, museum curators, archivists, local governments and anyone else who has data that they wish to share with the world. It is part of a wider ecosystem of tools and plugins dedicated to making working with structured data as productive as possible. Explore a demo , watch a presentation about the project or Try Datasette without installing anything using Glitch . More examples: https://datasette.io/examples Support questions, feedback? Join our GitHub Discussions forum . 8  
35 Contents Getting started Play with a live demo Try Datasette without installing anything using Glitch Using Datasette on your own computer datasette --get datasette serve --help Installation Basic installation Using Homebrew Using pip Advanced installation options Using pipx Using Docker The Datasette Ecosystem sqlite-utils Dogsheep Pages and API endpoints Top-level index Database Table Row Publishing data datasette publish Publishing to Google Cloud Run Publishing to Heroku Publishing to Vercel Publishing to Fly Custom metadata and plugins datasette package Deploying Datasette Deployment fundamentals Running Datasette using systemd Deploying using buildpacks Running Datasette behind a proxy Nginx proxy configuration Apache proxy configuration JSON API Different shapes Pagination Special JSON arguments Table arguments Column filter arguments Special table arguments Expanding foreign key references Running SQL queries Named parameters Views Canned queries Canned query parameters Setting a default fragment Writable canned queries Magic parameters JSON API for writable canned queries Pagination Cross-database queries Authentication and permissions Actors Using the "root" actor Permissions Defining permissions with "allow" blocks The /-/allow-debug tool Configuring permissions in metadata.json Controlling access to an instance Controlling access to specific databases Controlling access to specific tables and views Controlling access to specific canned queries Controlling the ability to execute arbitrary SQL Checking permissions in plugins actor_matches_allow() The permissions debug tool The ds_actor cookie Including an expiry time The /-/logout page Built-in permissions view-instance view-database view-database-download view-table view-query execute-sql permissions-debug debug-menu Performance and caching Immutable mode Using "datasette inspect" HTTP caching Hashed URL mode CSV export URL parameters Streaming all records A note on URLs Binary data Linking to binary downloads Binary plugins Facets Facets in query strings Facet… 8  
36 Publishing data Datasette includes tools for publishing and deploying your data to the internet. The datasette publish command will deploy a new Datasette instance containing your databases directly to a Heroku or Google Cloud hosting account. You can also use datasette package to create a Docker image that bundles your databases together with the datasette application that is used to serve them. 8  
37 datasette publish Once you have created a SQLite database (e.g. using csvs-to-sqlite ) you can deploy it to a hosting account using a single command. You will need a hosting account with Heroku or Google Cloud . Once you have created your account you will need to install and configure the heroku or gcloud command-line tools. 8  
38 Publishing to Google Cloud Run Google Cloud Run launched as a GA in in November 2019. It allows you to publish data in a scale-to-zero environment, so your application will start running when the first request is received and will shut down again when traffic ceases. This means you only pay for time spent serving traffic. You will first need to install and configure the Google Cloud CLI tools by following these instructions . You can then publish a database to Google Cloud Run using the following command: datasette publish cloudrun mydatabase.db --service=my-database A Cloud Run service is a single hosted application. The service name you specify will be used as part of the Cloud Run URL. If you deploy to a service name that you have used in the past your new deployment will replace the previous one. If you omit the --service option you will be asked to pick a service name interactively during the deploy. You may need to interact with prompts from the tool. Many of the prompts ask for values that can be set as properties for the Google Cloud SDK if you want to avoid the prompts. For example, the default region for the deployed instance can be set using the command: gcloud config set run/region us-central1 You should replace us-central1 with your desired region . Alternately, you can specify the region by setting the CLOUDSDK_RUN_REGION environment variable. Once it has finished it will output a URL like this one: Service [my-service] revision [my-service-00001] has been deployed and is serving traffic at https://my-service-j7hipcg4aq-uc.a.run.app Cloud Run provides a URL on the .run.app domain, but you can also point your own domain or subdomain at your Cloud Run service - see mapping custom domains in the Cloud Run documentation for details. $ datasette publish cloudrun --help Usage: datasette p… 8  
39 Publishing to Heroku To publish your data using Heroku , first create an account there and install and configure the Heroku CLI tool . You can publish a database to Heroku using the following command: datasette publish heroku mydatabase.db This will output some details about the new deployment, including a URL like this one: https://limitless-reef-88278.herokuapp.com/ deployed to Heroku You can specify a custom app name by passing -n my-app-name to the publish command. This will also allow you to overwrite an existing app. $ datasette publish heroku --help Usage: datasette publish heroku [OPTIONS] [FILES]... Options: -m, --metadata FILENAME Path to JSON/YAML file containing metadata to publish --extra-options TEXT Extra options to pass to datasette serve --branch TEXT Install datasette from a GitHub branch e.g. main --template-dir DIRECTORY Path to directory containing custom templates --plugins-dir DIRECTORY Path to directory containing custom plugins --static MOUNT:DIRECTORY Serve static files from this directory at /MOUNT/... --install TEXT Additional packages (e.g. plugins) to install --plugin-secret <TEXT TEXT TEXT>... Secrets to pass to plugins, e.g. --plugin-secret datasette-auth-github client_id xxx --version-note TEXT Additional note to show on /-/versions --secret TEXT Secret used for signing secure values, such as signed cookies --title TEXT Title for metadata --license TEXT License label for metadata --license_url TEXT License URL for metadata --source TEXT Source label for metadata --source_url TEXT Source URL for metadata --about TEXT About label for metadata --about_url T… 8  
40 Publishing to Vercel Vercel - previously known as Zeit Now - provides a layer over AWS Lambda to allow for quick, scale-to-zero deployment. You can deploy Datasette instances to Vercel using the datasette-publish-vercel plugin. pip install datasette-publish-vercel datasette publish vercel mydatabase.db --project my-database-project Not every feature is supported: consult the datasette-publish-vercel README for more details. 8  
41 Publishing to Fly Fly is a competitively priced Docker-compatible hosting platform that supports running applications in globally distributed data centers close to your end users. You can deploy Datasette instances to Fly using the datasette-publish-fly plugin. pip install datasette-publish-fly datasette publish fly mydatabase.db --app="my-app" Consult the datasette-publish-fly README for more details. 8  
42 Custom metadata and plugins datasette publish accepts a number of additional options which can be used to further customize your Datasette instance. You can define your own Metadata and deploy that with your instance like so: datasette publish cloudrun --service=my-service mydatabase.db -m metadata.json If you just want to set the title, license or source information you can do that directly using extra options to datasette publish : datasette publish cloudrun mydatabase.db --service=my-service \ --title="Title of my database" \ --source="Where the data originated" \ --source_url="http://www.example.com/" You can also specify plugins you would like to install. For example, if you want to include the datasette-vega visualization plugin you can use the following: datasette publish cloudrun mydatabase.db --service=my-service --install=datasette-vega If a plugin has any Secret configuration values you can use the --plugin-secret option to set those secrets at publish time. For example, using Heroku with datasette-auth-github you might run the following command: $ datasette publish heroku my_database.db \ --name my-heroku-app-demo \ --install=datasette-auth-github \ --plugin-secret datasette-auth-github client_id your_client_id \ --plugin-secret datasette-auth-github client_secret your_client_secret 8  
43 datasette package If you have docker installed (e.g. using Docker for Mac ) you can use the datasette package command to create a new Docker image in your local repository containing the datasette app bundled together with your selected SQLite databases: datasette package mydatabase.db Here's example output for the package command: $ datasette package parlgov.db --extra-options="--setting sql_time_limit_ms 2500" Sending build context to Docker daemon 4.459MB Step 1/7 : FROM python:3 ---> 79e1dc9af1c1 Step 2/7 : COPY . /app ---> Using cache ---> cd4ec67de656 Step 3/7 : WORKDIR /app ---> Using cache ---> 139699e91621 Step 4/7 : RUN pip install datasette ---> Using cache ---> 340efa82bfd7 Step 5/7 : RUN datasette inspect parlgov.db --inspect-file inspect-data.json ---> Using cache ---> 5fddbe990314 Step 6/7 : EXPOSE 8001 ---> Using cache ---> 8e83844b0fed Step 7/7 : CMD datasette serve parlgov.db --port 8001 --inspect-file inspect-data.json --setting sql_time_limit_ms 2500 ---> Using cache ---> 1bd380ea8af3 Successfully built 1bd380ea8af3 You can now run the resulting container like so: docker run -p 8081:8001 1bd380ea8af3 This exposes port 8001 inside the container as port 8081 on your host machine, so you can access the application at http://localhost:8081/ You can customize the port that is exposed by the countainer using the --port option: datasette package mydatabase.db --port 8080 A full list of options can be seen by running datasette package --help : $ datasette package --help Usage: datasette package [OPTIONS] FILES... Package specified SQLite files into a new datasette Docker container Options: -t, --tag TEXT Name for the resulting Docker container, can optionally use name:tag format -m, --metadata FILENAME Path to JSON/YAML file containing metadata to publish --extra-options TEXT Extra options to pass to data… 8  
44 Contributing Datasette is an open source project. We welcome contributions! This document describes how to contribute to Datasette core. You can also contribute to the wider Datasette ecosystem by creating new Plugins . 8  
45 General guidelines main should always be releasable . Incomplete features should live in branches. This ensures that any small bug fixes can be quickly released. The ideal commit should bundle together the implementation, unit tests and associated documentation updates. The commit message should link to an associated issue. New plugin hooks should only be shipped if accompanied by a separate release of a non-demo plugin that uses them. 8  
46 Setting up a development environment If you have Python 3.6 or higher installed on your computer (on OS X the quickest way to do this is using homebrew ) you can install an editable copy of Datasette using the following steps. If you want to use GitHub to publish your changes, first create a fork of datasette under your own GitHub account. Now clone that repository somewhere on your computer: git clone git@github.com:YOURNAME/datasette If you want to get started without creating your own fork, you can do this instead: git clone git@github.com:simonw/datasette The next step is to create a virtual environment for your project and use it to install Datasette's dependencies: cd datasette # Create a virtual environment in ./venv python3 -m venv ./venv # Now activate the virtual environment, so pip can install into it source venv/bin/activate # Install Datasette and its testing dependencies python3 -m pip install -e .[test] That last line does most of the work: pip install -e means "install this package in a way that allows me to edit the source code in place". The .[test] option means "use the setup.py in this directory and install the optional testing dependencies as well". 8  
47 Running the tests Once you have done this, you can run the Datasette unit tests from inside your datasette/ directory using pytest like so: pytest You can run the tests faster using multiple CPU cores with pytest-xdist like this: pytest -n auto -m "not serial" -n auto detects the number of available cores automatically. The -m "not serial" skips tests that don't work well in a parallel test environment. You can run those tests separately like so: pytest -m "serial" 8  
48 Using fixtures To run Datasette itself, type datasette . You're going to need at least one SQLite database. A quick way to get started is to use the fixtures database that Datasette uses for its own tests. You can create a copy of that database by running this command: python tests/fixtures.py fixtures.db Now you can run Datasette against the new fixtures database like so: datasette fixtures.db This will start a server at http://127.0.0.1:8001/ . Any changes you make in the datasette/templates or datasette/static folder will be picked up immediately (though you may need to do a force-refresh in your browser to see changes to CSS or JavaScript). If you want to change Datasette's Python code you can use the --reload option to cause Datasette to automatically reload any time the underlying code changes: datasette --reload fixtures.db You can also use the fixtures.py script to recreate the testing version of metadata.json used by the unit tests. To do that: python tests/fixtures.py fixtures.db fixtures-metadata.json Or to output the plugins used by the tests, run this: python tests/fixtures.py fixtures.db fixtures-metadata.json fixtures-plugins Test tables written to fixtures.db - metadata written to fixtures-metadata.json Wrote plugin: fixtures-plugins/register_output_renderer.py Wrote plugin: fixtures-plugins/view_name.py Wrote plugin: fixtures-plugins/my_plugin.py Wrote plugin: fixtures-plugins/messages_output_renderer.py Wrote plugin: fixtures-plugins/my_plugin_2.py Then run Datasette like this: datasette fixtures.db -m fixtures-metadata.json --plugins-dir=fixtures-plugins/ 8  
49 Debugging Any errors that occur while Datasette is running while display a stack trace on the console. You can tell Datasette to open an interactive pdb debugger session if an error occurs using the --pdb option: datasette --pdb fixtures.db 8  
50 Code formatting Datasette uses opinionated code formatters: Black for Python and Prettier for JavaScript. These formatters are enforced by Datasette's continuous integration: if a commit includes Python or JavaScript code that does not match the style enforced by those tools, the tests will fail. When developing locally, you can verify and correct the formatting of your code using these tools. 8  
51 Running Black Black will be installed when you run pip install -e '.[test]' . To test that your code complies with Black, run the following in your root datasette repository checkout: $ black . --check All done! ✨ 🍰 ✨ 95 files would be left unchanged. If any of your code does not conform to Black you can run this to automatically fix those problems: $ black . reformatted ../datasette/setup.py All done! ✨ 🍰 ✨ 1 file reformatted, 94 files left unchanged. 8  
52 Prettier To install Prettier, install Node.js and then run the following in the root of your datasette repository checkout: $ npm install This will install Prettier in a node_modules directory. You can then check that your code matches the coding style like so: $ npm run prettier -- --check > prettier > prettier 'datasette/static/*[!.min].js' "--check" Checking formatting... [warn] datasette/static/plugins.js [warn] Code style issues found in the above file(s). Forgot to run Prettier? You can fix any problems by running: $ npm run fix 8  
53 Editing and building the documentation Datasette's documentation lives in the docs/ directory and is deployed automatically using Read The Docs . The documentation is written using reStructuredText. You may find this article on The subset of reStructuredText worth committing to memory useful. You can build it locally by installing sphinx and sphinx_rtd_theme in your Datasette development environment and then running make html directly in the docs/ directory: # You may first need to activate your virtual environment: source venv/bin/activate # Install the dependencies needed to build the docs pip install -e .[docs] # Now build the docs cd docs/ make html This will create the HTML version of the documentation in docs/_build/html . You can open it in your browser like so: open _build/html/index.html Any time you make changes to a .rst file you can re-run make html to update the built documents, then refresh them in your browser. For added productivity, you can use use sphinx-autobuild to run Sphinx in auto-build mode. This will run a local webserver serving the docs that automatically rebuilds them and refreshes the page any time you hit save in your editor. sphinx-autobuild will have been installed when you ran pip install -e .[docs] . In your docs/ directory you can start the server by running the following: make livehtml Now browse to http://localhost:8000/ to view the documentation. Any edits you make should be instantly reflected in your browser. 8  
54 Release process Datasette releases are performed using tags. When a new release is published on GitHub, a GitHub Action workflow will perform the following: Run the unit tests against all supported Python versions. If the tests pass... Build a Docker image of the release and push a tag to https://hub.docker.com/r/datasetteproject/datasette Re-point the "latest" tag on Docker Hub to the new image Build a wheel bundle of the underlying Python source code Push that new wheel up to PyPI: https://pypi.org/project/datasette/ To deploy new releases you will need to have push access to the main Datasette GitHub repository. Datasette follows Semantic Versioning : major.minor.patch We increment major for backwards-incompatible releases. Datasette is currently pre-1.0 so the major version is always 0 . We increment minor for new features. We increment patch for bugfix releass. Alpha and beta releases may have an additional a0 or b0 prefix - the integer component will be incremented with each subsequent alpha or beta. To release a new version, first create a commit that updates the version number in datasette/version.py and the the changelog with highlights of the new version. An example commit can be seen here : # Update changelog git commit -m " Release 0.51a1 Refs #1056, #1039, #998, #1045, #1033, #1036, #1034, #976, #1057, #1058, #1053, #1064, #1066" -a git push Referencing the issues that are part of the release in the commit message ensures the name of the release shows up on those issue pages, e.g. here . You can generate the list of issue referen… 8  
55 Alpha and beta releases Alpha and beta releases are published to preview upcoming features that may not yet be stable - in particular to preview new plugin hooks. You are welcome to try these out, but please be aware that details may change before the final release. Please join discussions on the issue tracker to share your thoughts and experiences with on alpha and beta features that you try out. 8  
56 Releasing bug fixes from a branch If it's necessary to publish a bug fix release without shipping new features that have landed on main a release branch can be used. Create it from the relevant last tagged release like so: git branch 0.52.x 0.52.4 git checkout 0.52.x Next cherry-pick the commits containing the bug fixes: git cherry-pick COMMIT Write the release notes in the branch, and update the version number in version.py . Then push the branch: git push -u origin 0.52.x Once the tests have completed, publish the release from that branch target using the GitHub Draft a new release form. Finally, cherry-pick the commit with the release notes and version number bump across to main : git checkout main git cherry-pick COMMIT git push 8  
57 Upgrading CodeMirror Datasette bundles CodeMirror for the SQL editing interface, e.g. on this page . Here are the steps for upgrading to a new version of CodeMirror: Download and extract latest CodeMirror zip file from https://codemirror.net/codemirror.zip Rename lib/codemirror.js to codemirror-5.57.0.js (using latest version number) Rename lib/codemirror.css to codemirror-5.57.0.css Rename mode/sql/sql.js to codemirror-5.57.0-sql.js Edit both JavaScript files to make the top license comment a /* */ block instead of multiple // lines Minify the JavaScript files like this: npx uglify-js codemirror-5.57.0.js -o codemirror-5.57.0.min.js --comments '/LICENSE/' npx uglify-js codemirror-5.57.0-sql.js -o codemirror-5.57.0-sql.min.js --comments '/LICENSE/' Check that the LICENSE comment did indeed survive minification Minify the CSS file like this: npx clean-css-cli codemirror-5.57.0.css -o codemirror-5.57.0.min.css Edit the _codemirror.html template to reference the new files git rm the old files, git add the new files 8  
58 SpatiaLite The SpatiaLite module for SQLite adds features for handling geographic and spatial data. For an example of what you can do with it, see the tutorial Building a location to time zone API with SpatiaLite, OpenStreetMap and Datasette . To use it with Datasette, you need to install the mod_spatialite dynamic library. This can then be loaded into Datasette using the --load-extension command-line option. Datasette can look for SpatiaLite in common installation locations if you run it like this: datasette --load-extension=spatialite If SpatiaLite is in another location, use the full path to the extension instead: datasette --load-extension=/usr/local/lib/mod_spatialite.dylib 8  
59 Installation   8  
60 Installing SpatiaLite on OS X The easiest way to install SpatiaLite on OS X is to use Homebrew . brew update brew install spatialite-tools This will install the spatialite command-line tool and the mod_spatialite dynamic library. You can now run Datasette like so: datasette --load-extension=spatialite 8  
61 Installing SpatiaLite on Linux SpatiaLite is packaged for most Linux distributions. apt install spatialite-bin libsqlite3-mod-spatialite Depending on your distribution, you should be able to run Datasette something like this: datasette --load-extension=/usr/lib/x86_64-linux-gnu/mod_spatialite.so If you are unsure of the location of the module, try running locate mod_spatialite and see what comes back. 8  
62 Spatial indexing latitude/longitude columns Here's a recipe for taking a table with existing latitude and longitude columns, adding a SpatiaLite POINT geometry column to that table, populating the new column and then populating a spatial index: import sqlite3 conn = sqlite3.connect('museums.db') # Lead the spatialite extension: conn.enable_load_extension(True) conn.load_extension('/usr/local/lib/mod_spatialite.dylib') # Initialize spatial metadata for this database: conn.execute('select InitSpatialMetadata(1)') # Add a geometry column called point_geom to our museums table: conn.execute("SELECT AddGeometryColumn('museums', 'point_geom', 4326, 'POINT', 2);") # Now update that geometry column with the lat/lon points conn.execute(''' UPDATE museums SET point_geom = GeomFromText('POINT('||"longitude"||' '||"latitude"||')',4326); ''') # Now add a spatial index to that column conn.execute('select CreateSpatialIndex("museums", "point_geom");') # If you don't commit your changes will not be persisted: conn.commit() conn.close() 8  
63 Making use of a spatial index SpatiaLite spatial indexes are R*Trees. They allow you to run efficient bounding box queries using a sub-select, with a similar pattern to that used for Searches using custom SQL . In the above example, the resulting index will be called idx_museums_point_geom . This takes the form of a SQLite virtual table. You can inspect its contents using the following query: select * from idx_museums_point_geom limit 10; Here's a live example: timezones-api.datasette.io/timezones/idx_timezones_Geometry pkid xmin xmax ymin ymax 1 -8.601725578308105 -2.4930307865142822 4.162120819091797 10.74019718170166 2 … 8  
64 Importing shapefiles into SpatiaLite The shapefile format is a common format for distributing geospatial data. You can use the spatialite command-line tool to create a new database table from a shapefile. Try it now with the North America shapefile available from the University of North Carolina Global River Database project. Download the file and unzip it (this will create files called narivs.dbf , narivs.prj , narivs.shp and narivs.shx in the current directory), then run the following: $ spatialite rivers-database.db SpatiaLite version ..: 4.3.0a Supported Extensions: ... spatialite> .loadshp narivs rivers CP1252 23032 ======== Loading shapefile at 'narivs' into SQLite table 'rivers' ... Inserted 467973 rows into 'rivers' from SHAPEFILE This will load the data from the narivs shapefile into a new database table called rivers . Exit out of spatialite (using Ctrl+D ) and run Datasette against your new database like this: datasette rivers-database.db \ --load-extension=/usr/local/lib/mod_spatialite.dylib If you browse to http://localhost:8001/rivers-database/rivers you will see the new table... but the Geometry column will contain unreadable binary data (SpatiaLite uses a custom format based on WKB ). The easiest way to turn this into semi-readable data is to use the SpatiaLite AsGeoJSON function. Try the following using the SQL query interface at http://localhost:8001/rivers-database : select *, AsGeoJSON(Geometry) from rivers limit 10; This will give you back an additional column of GeoJSON. You can copy and paste GeoJSON from this column into the debugging tool at geojson.io to visualize it on a map. To see a more interesting example, try ordering the records with the longest geometry first. Since there are 467,000 rows in the table you will first need to increase the SQL time limit imposed by Datasette: datasette rivers-database.db \ --load-extension=/us… 8  
65 Importing GeoJSON polygons using Shapely Another common form of polygon data is the GeoJSON format. This can be imported into SpatiaLite directly, or by using the Shapely Python library. Who's On First is an excellent source of openly licensed GeoJSON polygons. Let's import the geographical polygon for Wales. First, we can use the Who's On First Spelunker tool to find the record for Wales: spelunker.whosonfirst.org/id/404227475 That page includes a link to the GeoJSON record, which can be accessed here: data.whosonfirst.org/404/227/475/404227475.geojson Here's Python code to create a SQLite database, enable SpatiaLite, create a places table and then add a record for Wales: import sqlite3 conn = sqlite3.connect('places.db') # Enable SpatialLite extension conn.enable_load_extension(True) conn.load_extension('/usr/local/lib/mod_spatialite.dylib') # Create the masic countries table conn.execute('select InitSpatialMetadata(1)') conn.execute('create table places (id integer primary key, name text);') # Add a MULTIPOLYGON Geometry column conn.execute("SELECT AddGeometryColumn('places', 'geom', 4326, 'MULTIPOLYGON', 2);") # Add a spatial index against the new column conn.execute("SELECT CreateSpatialIndex('places', 'geom');") # Now populate the table from shapely.geometry.multipolygon import MultiPolygon from shapely.geometry import shape import requests geojson = requests.get('https://data.whosonfirst.org/404/227/475/404227475.geojson').json() # Convert to "Well Known Text" format wkt = shape(geojson['geometry']).wkt # Insert and commit the record conn.execute("INSERT INTO places (id, name, geom) VALUES(null, ?, GeomFromText(?, 4326))", ( "Wales", wkt )) conn.commit() 8  
66 Querying polygons using within() The within() SQL function can be used to check if a point is within a geometry: select name from places where within(GeomFromText('POINT(-3.1724366 51.4704448)'), places.geom); The GeomFromText() function takes a string of well-known text. Note that the order used here is longitude then latitude . To run that same within() query in a way that benefits from the spatial index, use the following: select name from places where within(GeomFromText('POINT(-3.1724366 51.4704448)'), places.geom) and rowid in ( SELECT pkid FROM idx_places_geom where xmin < -3.1724366 and xmax > -3.1724366 and ymin < 51.4704448 and ymax > 51.4704448 ); 8  
67 Performance and caching Datasette runs on top of SQLite, and SQLite has excellent performance. For small databases almost any query should return in just a few milliseconds, and larger databases (100s of MBs or even GBs of data) should perform extremely well provided your queries make sensible use of database indexes. That said, there are a number of tricks you can use to improve Datasette's performance. 8  
68 Immutable mode If you can be certain that a SQLite database file will not be changed by another process you can tell Datasette to open that file in immutable mode . Doing so will disable all locking and change detection, which can result in improved query performance. This also enables further optimizations relating to HTTP caching, described below. To open a file in immutable mode pass it to the datasette command using the -i option: datasette -i data.db When you open a file in immutable mode like this Datasette will also calculate and cache the row counts for each table in that database when it first starts up, further improving performance. 8  
69 Using "datasette inspect" Counting the rows in a table can be a very expensive operation on larger databases. In immutable mode Datasette performs this count only once and caches the results, but this can still cause server startup time to increase by several seconds or more. If you know that a database is never going to change you can precalculate the table row counts once and store then in a JSON file, then use that file when you later start the server. To create a JSON file containing the calculated row counts for a database, use the following: datasette inspect data.db --inspect-file=counts.json Then later you can start Datasette against the counts.json file and use it to skip the row counting step and speed up server startup: datasette -i data.db --inspect-file=counts.json You need to use the -i immutable mode against the databse file here or the counts from the JSON file will be ignored. You will rarely need to use this optimization in every-day use, but several of the datasette publish commands described in Publishing data use this optimization for better performance when deploying a database file to a hosting provider. 8  
70 HTTP caching If your database is immutable and guaranteed not to change, you can gain major performance improvements from Datasette by enabling HTTP caching. This can work at two different levels. First, it can tell browsers to cache the results of queries and serve future requests from the browser cache. More significantly, it allows you to run Datasette behind a caching proxy such as Varnish or use a cache provided by a hosted service such as Fastly or Cloudflare . This can provide incredible speed-ups since a query only needs to be executed by Datasette the first time it is accessed - all subsequent hits can then be served by the cache. Using a caching proxy in this way could enable a Datasette-backed visualization to serve thousands of hits a second while running Datasette itself on extremely inexpensive hosting. Datasette's integration with HTTP caches can be enabled using a combination of configuration options and query string arguments. The default_cache_ttl setting sets the default HTTP cache TTL for all Datasette pages. This is 5 seconds unless you change it - you can set it to 0 if you wish to disable HTTP caching entirely. You can also change the cache timeout on a per-request basis using the ?_ttl=10 query string parameter. This can be useful when you are working with the Datasette JSON API - you may decide that a specific query can be cached for a longer time, or maybe you need to set ?_ttl=0 for some requests for example if you are running a SQL order by random() query. 8  
71 Hashed URL mode When you open a database file in immutable mode using the -i option, Datasette calculates a SHA-256 hash of the contents of that file on startup. This content hash can then optionally be used to create URLs that are guaranteed to change if the contents of the file changes in the future. This results in URLs that can then be cached indefinitely by both browsers and caching proxies - an enormous potential performance optimization. You can enable these hashed URLs in two ways: using the hash_urls configuration setting (which affects all requests to Datasette) or via the ?_hash=1 query string parameter (which only applies to the current request). With hashed URLs enabled, any request to e.g. /mydatabase/mytable will 302 redirect to mydatabase-455fe3a/mytable . The URL containing the hash will be served with a very long cache expire header - configured using default_cache_ttl_hashed which defaults to 365 days. Since these responses are cached for a long time, you may wish to build API clients against the non-hashed version of these URLs. These 302 redirects are served extremely quickly, so this should still be a performant way to work against the Datasette API. If you run Datasette behind an HTTP/2 server push aware proxy such as Cloudflare Datasette will serve the 302 redirects in such a way that the redirected page will be efficiently "pushed" to the browser as part of the response, without the browser needing to make a second HTTP request to fetch the redirected resource. Prior to Datasette 0.28 hashed URL mode was the default behaviour for Datasette, since all database files were assumed to be immutable and unchanging. From 0.28 onwards the default has been to treat database files as mutable unless explicitly configured otherwise. 8  
72 Binary data SQLite tables can contain binary data in BLOB columns. Datasette includes special handling for these binary values. The Datasette interface detects binary values and provides a link to download their content, for example on https://latest.datasette.io/fixtures/binary_data Binary data is represented in .json exports using Base64 encoding. https://latest.datasette.io/fixtures/binary_data.json?_shape=array [ { "rowid": 1, "data": { "$base64": true, "encoded": "FRwCx60F/g==" } }, { "rowid": 2, "data": { "$base64": true, "encoded": "FRwDx60F/g==" } }, { "rowid": 3, "data": null } ] 8  
73 Linking to binary downloads The .blob output format is used to return binary data. It requires a _blob_column= query string argument specifying which BLOB column should be downloaded, for example: https://latest.datasette.io/fixtures/binary_data/1.blob?_blob_column=data This output format can also be used to return binary data from an arbitrary SQL query. Since such queries do not specify an exact row, an additional ?_blob_hash= parameter can be used to specify the SHA-256 hash of the value that is being linked to. Consider the query select data from binary_data - demonstrated here . That page links to the binary value downloads. Those links look like this: https://latest.datasette.io/fixtures.blob?sql=select+data+from+binary_data&_blob_column=data&_blob_hash=f3088978da8f9aea479ffc7f631370b968d2e855eeb172bea7f6c7a04262bb6d These .blob links are also returned in the .csv exports Datasette provides for binary tables and queries, since the CSV format does not have a mechanism for representing binary data. 8  
74 Binary plugins Several Datasette plugins are available that change the way Datasette treats binary data. datasette-render-binary modifies Datasette's default interface to show an automatic guess at what type of binary data is being stored, along with a visual representation of the binary value that displays ASCII strings directly in the interface. datasette-render-images detects common image formats and renders them as images directly in the Datasette interface. datasette-media allows Datasette interfaces to be configured to serve binary files from configured SQL queries, and includes the ability to resize images directly before serving them. 8  
75 Plugins Datasette's plugin system allows additional features to be implemented as Python code (or front-end JavaScript) which can be wrapped up in a separate Python package. The underlying mechanism uses pluggy . See the Datasette plugins directory for a list of existing plugins, or take a look at the datasette-plugin topic on GitHub. Things you can do with plugins include: Add visualizations to Datasette, for example datasette-cluster-map and datasette-vega . Make new custom SQL functions available for use within Datasette, for example datasette-haversine and datasette-jellyfish . Define custom output formats with custom extensions, for example datasette-atom and datasette-ics . Add template functions that can be called within your Jinja custom templates, for example datasette-render-markdown . Customize how database values are rendered in the Datasette interface, for example datasette-render-binary and datasette-pretty-json . Customize how Datasette's authentication and permissions systems work, for example datasette-auth-tokens and datasette-permissions-sql . 8  
76 Installing plugins If a plugin has been packaged for distribution using setuptools you can use the plugin by installing it alongside Datasette in the same virtual environment or Docker container. You can install plugins using the datasette install command: datasette install datasette-vega You can uninstall plugins with datasette uninstall : datasette uninstall datasette-vega You can upgrade plugins with datasette install --upgrade or datasette install -U : datasette install -U datasette-vega This command can also be used to upgrade Datasette itself to the latest released version: datasette install -U datasette These commands are thin wrappers around pip install and pip uninstall , which ensure they run pip in the same virtual environment as Datasette itself. 8  
77 One-off plugins using --plugins-dir You can also define one-off per-project plugins by saving them as plugin_name.py functions in a plugins/ folder and then passing that folder to datasette using the --plugins-dir option: datasette mydb.db --plugins-dir=plugins/ 8  
78 Deploying plugins using datasette publish The datasette publish and datasette package commands both take an optional --install argument. You can use this one or more times to tell Datasette to pip install specific plugins as part of the process: datasette publish cloudrun mydb.db --install=datasette-vega You can use the name of a package on PyPI or any of the other valid arguments to pip install such as a URL to a .zip file: datasette publish cloudrun mydb.db \ --install=https://url-to-my-package.zip 8  
79 Seeing what plugins are installed You can see a list of installed plugins by navigating to the /-/plugins page of your Datasette instance - for example: https://fivethirtyeight.datasettes.com/-/plugins You can also use the datasette plugins command: $ datasette plugins [ { "name": "datasette_json_html", "static": false, "templates": false, "version": "0.4.0" } ] If you run datasette plugins --all it will include default plugins that ship as part of Datasette: $ datasette plugins --all [ { "name": "datasette.sql_functions", "static": false, "templates": false, "version": null }, { "name": "datasette.publish.cloudrun", "static": false, "templates": false, "version": null }, { "name": "datasette.facets", "static": false, "templates": false, "version": null }, { "name": "datasette.publish.heroku", "static": false, "templates": false, "version": null } ] You can add the --plugins-dir= option to include any plugins found in that directory. 8  
80 Plugin configuration Plugins can have their own configuration, embedded in a Metadata file. Configuration options for plugins live within a "plugins" key in that file, which can be included at the root, database or table level. Here is an example of some plugin configuration for a specific table: { "databases": { "sf-trees": { "tables": { "Street_Tree_List": { "plugins": { "datasette-cluster-map": { "latitude_column": "lat", "longitude_column": "lng" } } } } } } } This tells the datasette-cluster-map column which latitude and longitude columns should be used for a table called Street_Tree_List inside a database file called sf-trees.db . 8  
81 Secret configuration values Any values embedded in metadata.json will be visible to anyone who views the /-/metadata page of your Datasette instance. Some plugins may need configuration that should stay secret - API keys for example. There are two ways in which you can store secret configuration values. As environment variables . If your secret lives in an environment variable that is available to the Datasette process, you can indicate that the configuration value should be read from that environment variable like so: { "plugins": { "datasette-auth-github": { "client_secret": { "$env": "GITHUB_CLIENT_SECRET" } } } } As values in separate files . Your secrets can also live in files on disk. To specify a secret should be read from a file, provide the full file path like this: { "plugins": { "datasette-auth-github": { "client_secret": { "$file": "/secrets/client-secret" } } } } If you are publishing your data using the datasette publish family of commands, you can use the --plugin-secret option to set these secrets at publish time. For example, using Heroku you might run the following command: $ datasette publish heroku my_database.db \ --name my-heroku-app-demo \ --install=datasette-auth-github \ --plugin-secret datasette-auth-github client_id your_client_id \ --plugin-secret datasette-auth-github client_secret your_client_secret This will set the necessary environment variables and add the following to the deployed metadata.json : { "plugins": { "datasette-auth-github": { "client_id": { "$env": "DATASETTE_AUTH_GITHUB_CLIENT_ID" }, "client_secret": { "$env": "DATASETTE_AUTH_GITHUB_CLIENT_SECRET" } } } } 8  
82 Facets Datasette facets can be used to add a faceted browse interface to any database table. With facets, tables are displayed along with a summary showing the most common values in specified columns. These values can be selected to further filter the table. Facets can be specified in two ways: using query string parameters, or in metadata.json configuration for the table. 8  
83 Facets in query strings To turn on faceting for specific columns on a Datasette table view, add one or more _facet=COLUMN parameters to the URL. For example, if you want to turn on facets for the city_id and state columns, construct a URL that looks like this: /dbname/tablename?_facet=state&_facet=city_id This works for both the HTML interface and the .json view. When enabled, facets will cause a facet_results block to be added to the JSON output, looking something like this: { "state": { "name": "state", "results": [ { "value": "CA", "label": "CA", "count": 10, "toggle_url": "http://...?_facet=city_id&_facet=state&state=CA", "selected": false }, { "value": "MI", "label": "MI", "count": 4, "toggle_url": "http://...?_facet=city_id&_facet=state&state=MI", "selected": false }, { "value": "MC", "label": "MC", "count": 1, "toggle_url": "http://...?_facet=city_id&_facet=state&state=MC", "selected": false } ], "truncated": false } "city_id": { "name": "city_id", "results": [ { "value": 1, "label": "San Francisco", "count": 6, "toggle_url": "http://...?_facet=city_id&_facet=state&city_id=1", "selected": false }, { "value": 2, "label": "Los Angeles", "count": 4, "toggle_url": "http://...?_facet=city_id&_facet=state&city_id=2", "selected": false }, { "value": 3, "label": "Detroit", "count": 4, "toggle_url": "http://...?_facet=city_id&_facet=state&city_id=3", "selected": false }, { "value": 4, "label": "Memnonia", "count": 1, "toggle_url": "http://...?_facet=city_id&_facet=state&city_id=4", "selected": false } ], "truncated": false } } If Datasette detects that a column is a foreign key… 8  
84 Facets in metadata.json You can turn facets on by default for specific tables by adding them to a "facets" key in a Datasette Metadata file. Here's an example that turns on faceting by default for the qLegalStatus column in the Street_Tree_List table in the sf-trees database: { "databases": { "sf-trees": { "tables": { "Street_Tree_List": { "facets": ["qLegalStatus"] } } } } } Facets defined in this way will always be shown in the interface and returned in the API, regardless of the _facet arguments passed to the view. 8  
85 Suggested facets Datasette's table UI will suggest facets for the user to apply, based on the following criteria: For the currently filtered data are there any columns which, if applied as a facet... Will return 30 or less unique options Will return more than one unique option Will return less unique options than the total number of filtered rows And the query used to evaluate this criteria can be completed in under 50ms That last point is particularly important: Datasette runs a query for every column that is displayed on a page, which could get expensive - so to avoid slow load times it sets a time limit of just 50ms for each of those queries. This means suggested facets are unlikely to appear for tables with millions of records in them. 8  
86 Speeding up facets with indexes The performance of facets can be greatly improved by adding indexes on the columns you wish to facet by. Adding indexes can be performed using the sqlite3 command-line utility. Here's how to add an index on the state column in a table called Food_Trucks : $ sqlite3 mydatabase.db SQLite version 3.19.3 2017-06-27 16:48:08 Enter ".help" for usage hints. sqlite> CREATE INDEX Food_Trucks_state ON Food_Trucks("state"); 8  
87 Facet by JSON array If your SQLite installation provides the json1 extension (you can check using /-/versions ) Datasette will automatically detect columns that contain JSON arrays of values and offer a faceting interface against those columns. This is useful for modelling things like tags without needing to break them out into a new table. Example here: latest.datasette.io/fixtures/facetable?_facet_array=tags 8  
88 Facet by date If Datasette finds any columns that contain dates in the first 100 values, it will offer a faceting interface against the dates of those values. This works especially well against timestamp values such as 2019-03-01 12:44:00 . Example here: latest.datasette.io/fixtures/facetable?_facet_date=created 8  
89 CSV export Any Datasette table, view or custom SQL query can be exported as CSV. To obtain the CSV representation of the table you are looking, click the "this data as CSV" link. You can also use the advanced export form for more control over the resulting file, which looks like this and has the following options: download file - instead of displaying CSV in your browser, this forces your browser to download the CSV to your downloads directory. expand labels - if your table has any foreign key references this option will cause the CSV to gain additional COLUMN_NAME_label columns with a label for each foreign key derived from the linked table. In this example the city_id column is accompanied by a city_id_label column. stream all rows - by default CSV files only contain the first max_returned_rows records. This option will cause Datasette to loop through every matching record and return them as a single CSV file. You can try that out on https://latest.datasette.io/fixtures/facetable?_size=4 8  
90 URL parameters The following options can be used to customize the CSVs returned by Datasette. ?_header=off This removes the first row of the CSV file specifying the headings - only the row data will be returned. ?_stream=on Stream all matching records, not just the first page of results. See below. ?_dl=on Causes Datasette to return a content-disposition: attachment; filename="filename.csv" header. 8  
91 Streaming all records The stream all rows option is designed to be as efficient as possible - under the hood it takes advantage of Python 3 asyncio capabilities and Datasette's efficient pagination to stream back the full CSV file. Since databases can get pretty large, by default this option is capped at 100MB - if a table returns more than 100MB of data the last line of the CSV will be a truncation error message. You can increase or remove this limit using the max_csv_mb config setting. You can also disable the CSV export feature entirely using allow_csv_stream . 8  
92 A note on URLs The default URL for the CSV representation of a table is that table with .csv appended to it: https://latest.datasette.io/fixtures/facetable - HTML interface https://latest.datasette.io/fixtures/facetable.csv - CSV export https://latest.datasette.io/fixtures/facetable.json - JSON API This pattern doesn't work for tables with names that already end in .csv or .json . For those tables, you can instead use the _format= query string parameter: https://latest.datasette.io/fixtures/table%2Fwith%2Fslashes.csv - HTML interface https://latest.datasette.io/fixtures/table%2Fwith%2Fslashes.csv?_format=csv - CSV export https://latest.datasette.io/fixtures/table%2Fwith%2Fslashes.csv?_format=json - JSON API 8  
93 Installation If you just want to try Datasette out you don't need to install anything: see Try Datasette without installing anything using Glitch There are two main options for installing Datasette. You can install it directly on to your machine, or you can install it using Docker. If you want to start making contributions to the Datasette project by installing a copy that lets you directly modify the code, take a look at our guide to Setting up a development environment . Basic installation Using Homebrew Using pip Advanced installation options Using pipx Upgrading packages using pipx Using Docker Loading SpatiaLite Installing plugins 8  
94 Basic installation   8  
95 Using Homebrew If you have a Mac and use Homebrew , you can install Datasette by running this command in your terminal: brew install datasette This should install the latest version. You can confirm by running: datasette --version You can upgrade to the latest Homebrew packaged version using: brew upgrade datasette Once you have installed Datasette you can install plugins using the following: datasette install datasette-vega If the latest packaged release of Datasette has not yet been made available through Homebrew, you can upgrade your Homebrew installation in-place using: datasette install -U datasette 8  
96 Using pip Datasette requires Python 3.6 or higher. Visit InstallPython3.com for step-by-step installation guides for your operating system. You can install Datasette and its dependencies using pip : pip install datasette You can now run Datasette like so: datasette 8  
97 Advanced installation options   8  
98 Using pipx pipx is a tool for installing Python software with all of its dependencies in an isolated environment, to ensure that they will not conflict with any other installed Python software. If you use Homebrew on macOS you can install pipx like this: brew install pipx pipx ensurepath Without Homebrew you can install it like so: python3 -m pip install --user pipx python3 -m pipx ensurepath The pipx ensurepath command configures your shell to ensure it can find commands that have been installed by pipx - generally by making sure ~/.local/bin has been added to your PATH . Once pipx is installed you can use it to install Datasette like this: pipx install datasette Then run datasette --version to confirm that it has been successfully installed. 8  
99 Upgrading packages using pipx You can upgrade your pipx installation to the latest release of Datasette using pipx upgrade datasette : $ pipx upgrade datasette upgraded package datasette from 0.39 to 0.40 (location: /Users/simon/.local/pipx/venvs/datasette) To upgrade a plugin within the pipx environment use pipx runpip datasette install -U name-of-plugin - like this: % datasette plugins [ { "name": "datasette-vega", "static": true, "templates": false, "version": "0.6" } ] $ pipx runpip datasette install -U datasette-vega Collecting datasette-vega Downloading datasette_vega-0.6.2-py3-none-any.whl (1.8 MB) |████████████████████████████████| 1.8 MB 2.0 MB/s ... Installing collected packages: datasette-vega Attempting uninstall: datasette-vega Found existing installation: datasette-vega 0.6 Uninstalling datasette-vega-0.6: Successfully uninstalled datasette-vega-0.6 Successfully installed datasette-vega-0.6.2 $ datasette plugins [ { "name": "datasette-vega", "static": true, "templates": false, "version": "0.6.2" } ] 8  
100 Using Docker A Docker image containing the latest release of Datasette is published to Docker Hub here: https://hub.docker.com/r/datasetteproject/datasette/ If you have Docker installed (for example with Docker for Mac on OS X) you can download and run this image like so: docker run -p 8001:8001 -v `pwd`:/mnt \ datasetteproject/datasette \ datasette -p 8001 -h 0.0.0.0 /mnt/fixtures.db This will start an instance of Datasette running on your machine's port 8001, serving the fixtures.db file in your current directory. Now visit http://127.0.0.1:8001/ to access Datasette. (You can download a copy of fixtures.db from https://latest.datasette.io/fixtures.db ) To upgrade to the most recent release of Datasette, run the following: docker pull datasetteproject/datasette 8  

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CREATE VIRTUAL TABLE [sections_fts] USING FTS5 (
    [title], [content],
    tokenize='porter',
    content=[sections]
);