id,page,ref,title,content,breadcrumbs,references
sql_queries:canned-queries-magic-parameters,sql_queries,canned-queries-magic-parameters,Magic parameters,"Named parameters that start with an underscore are special: they can be used to automatically add values created by Datasette that are not contained in the incoming form fields or query string. 
                 These magic parameters are only supported for canned queries: to avoid security issues (such as queries that extract the user's private cookies) they are not available to SQL that is executed by the user as a custom SQL query. 
                 Available magic parameters are: 
                 
                     
                         _actor_*  - e.g.  _actor_id ,  _actor_name 
                         
                             Fields from the currently authenticated  Actors . 
                         
                     
                     
                         _header_*  - e.g.  _header_user_agent 
                         
                             Header from the incoming HTTP request. The key should be in lower case and with hyphens converted to underscores e.g.  _header_user_agent  or  _header_accept_language . 
                         
                     
                     
                         _cookie_*  - e.g.  _cookie_lang 
                         
                             The value of the incoming cookie of that name. 
                         
                     
                     
                         _now_epoch 
                         
                             The number of seconds since the Unix epoch. 
                         
                     
                     
                         _now_date_utc 
                         
                             The date in UTC, e.g.  2020-06-01 
                         
                     
                     
                         _now_datetime_utc 
                         
                             The ISO 8601 datetime in UTC, e.g.  2020-06-24T18:01:07Z 
                         
                     
                     
                         _random_chars_*  - e.g.  _random_chars_128 
                         
                             A random string of characters of the specified length. 
                         
                     
                 
                 Here's an example configuration that adds a message from the authenticated user, storing various pieces of additional metadata using magic parameters: 
                 [[[cog
config_example(cog, """"""
databases:
  mydatabase:
    queries:
      add_message:
        allow:
          id: ""*""
        sql: |-
          INSERT INTO messages (
            user_id, message, datetime
          ) VALUES (
            :_actor_id, :message, :_now_datetime_utc
          )
        write: true
"""""") 
                 ]]] 
                 [[[end]]] 
                 The form presented at  /mydatabase/add_message  will have just a field for  message  - the other parameters will be populated by the magic parameter mechanism. 
                 Additional custom magic parameters can be added by plugins using the  register_magic_parameters(datasette)  hook.","[""Running SQL queries"", ""Canned queries""]",[]