Many :ref:`plugin_hooks` are passed objects that provide access to internal Datasette functionality. The interface to these objects should not be considered stable with the exception of methods that are documented here.
The request object is passed to various plugin hooks. It represents an incoming HTTP request. It has the following properties:
``.scope`` - dictionary
The ASGI scope that was used to construct this request, described in the `ASGI HTTP connection scope <https://asgi.readthedocs.io/en/latest/specs/www.html#connection-scope>`__ specification.
``.method`` - string
The HTTP method for this request, usually ``GET`` or ``POST``.
``.url`` - string
The full URL for this request, e.g. ``https://latest.datasette.io/fixtures``.
``.scheme`` - string
The request scheme - usually ``https`` or ``http``.
Parses form data from the request body. Supports both ``application/x-www-form-urlencoded`` and ``multipart/form-data`` content types.
Returns a :ref:`internals_formdata` object with dict-like access to form fields and uploaded files.
Requirements and errors:
- A ``Content-Type`` header is required. Missing or unsupported content types raise ``BadRequest``.
- For ``multipart/form-data``, the ``boundary=...`` parameter is required.
Parameters:
-``files`` (bool, default ``False``): If ``True``, uploaded files are stored and accessible. If ``False`` (default), file content is discarded but form fields are still available.
-``max_file_size`` (int, default 50MB): Maximum size per uploaded file in bytes.
-``max_request_size`` (int, default 100MB): Maximum total request body size in bytes.
-``max_fields`` (int, default 1000): Maximum number of form fields.
-``max_files`` (int, default 100): Maximum number of uploaded files.
-``max_parts`` (int, default ``max_fields + max_files``): Maximum number of multipart parts in total.
-``max_field_size`` (int, default 100KB): Maximum size of a text field value in bytes.
-``max_memory_file_size`` (int, default 1MB): File size threshold before uploads spill to disk.
-``max_part_header_bytes`` (int, default 16KB): Maximum total bytes allowed in part headers.
-``max_part_header_lines`` (int, default 100): Maximum header lines per part.
-``min_free_disk_bytes`` (int, default 50MB): Minimum free bytes required in the temp directory before accepting file uploads.
Returns a dictionary of form variables that were submitted in the request body via ``POST`` using ``application/x-www-form-urlencoded`` encoding. For multipart forms or file uploads, use ``request.form()`` instead.
``request.args`` is a ``MultiParams`` object - a dictionary-like object which provides access to query string parameters that may have multiple values.
Returns the first value for that key, or raises a ``KeyError`` if the key is missing. For the above example ``request.args["foo"]`` would return ``"1"``.
``request.args.get(key)`` - string or None
Returns the first value for that key, or ``None`` if the key is missing. Pass a second argument to specify a different default, e.g. ``q = request.args.get("q", "")``.
``request.args.getlist(key)`` - list of strings
Returns the list of strings for that key. ``request.args.getlist("foo")`` would return ``["1", "2"]`` in the above example. ``request.args.getlist("bar")`` would return ``["3"]``. If the key is missing an empty list will be returned.
``request.args.keys()`` - list of strings
Returns the list of available keys - for the example this would be ``["foo", "bar"]``.
``key in request.args`` - True or False
You can use ``if key in request.args`` to check if a key is present.
``await request.form()`` returns a ``FormData`` object - a dictionary-like object which provides access to form fields and uploaded files. It has a similar interface to ``MultiParams``.
``form[key]`` - string or UploadedFile
Returns the first value for that key, or raises a ``KeyError`` if the key is missing.
``form.get(key)`` - string, UploadedFile, or None
Returns the first value for that key, or ``None`` if the key is missing. Pass a second argument to specify a different default.
``form.getlist(key)`` - list
Returns the list of values for that key. If the key is missing an empty list will be returned.
``form.keys()`` - list of strings
Returns the list of available keys.
``key in form`` - True or False
You can use ``if key in form`` to check if a key is present.
``for key in form`` - iterator
This lets you loop through every available key.
``len(form)`` - integer
Returns the total number of submitted values.
.._internals_uploadedfile:
The UploadedFile class
======================
When parsing multipart form data with ``files=True``, file uploads are returned as ``UploadedFile`` objects with the following properties and methods:
``uploaded_file.name`` - string
The form field name.
``uploaded_file.filename`` - string
The original filename provided by the client. Note: This is sanitized to remove path components for security.
``uploaded_file.content_type`` - string or None
The MIME type of the uploaded file, if provided by the client.
``uploaded_file.size`` - integer
The size of the uploaded file in bytes.
``await uploaded_file.read(size=-1)`` - bytes
Read and return up to ``size`` bytes from the file. If ``size`` is -1 (default), read the entire file.
Seek to the given position in the file. Returns the new position.
``await uploaded_file.close()``
Close the underlying file. This is called automatically when the object is garbage collected.
Files smaller than 1MB are stored in memory. Larger files are automatically spilled to temporary files on disk and cleaned up when the request completes.
The quickest way to create responses is using the ``Response.text(...)``, ``Response.html(...)``, ``Response.json(...)`` or ``Response.redirect(...)`` helper methods:
Each of these responses will use the correct corresponding content-type - ``text/html; charset=utf-8``, ``application/json; charset=utf-8`` or ``text/plain; charset=utf-8`` respectively.
Each of the helper methods take optional ``status=`` and ``headers=`` arguments, documented above.
In most cases you will return ``Response`` objects from your own view functions. You can also use a ``Response`` instance to respond at a lower level via ASGI, for example if you are writing code that uses the :ref:`plugin_asgi_wrapper` hook.
Create a ``Response`` object and then use ``await response.asgi_send(send)``, passing the ASGI ``send`` function. For example:
You can use this with :ref:`datasette.sign() <datasette_sign>` to set signed cookies. Here's how you would set the :ref:`ds_actor cookie <authentication_ds_actor>` for use with Datasette :ref:`authentication <authentication>`:
The dictionary keys are the name of the database that is used in the URL - e.g. ``/fixtures`` would have a key of ``"fixtures"``. The values are :ref:`internals_database` instances.
This method lets you read plugin configuration values that were set in ``datasette.yaml``. See :ref:`writing_plugins_configuration` for full details of how this method should be used.
The template file to be rendered, e.g. ``my_plugin.html``. Datasette will search for this file first in the ``--template-dir=`` location, if it was specified - then in the plugin's bundled templates and finally in Datasette's set of default templates.
If you pass a Datasette request object here it will be made available to the template.
Renders a `Jinja template <https://jinja.palletsprojects.com/en/2.11.x/>`__ using Datasette's preconfigured instance of Jinja and returns the resulting string. The template will have access to Datasette's default template functions and any functions that have been made available by other plugins.
The name of the action that is being permission checked.
``resource`` - Resource object
A Resource object representing the database, table, or other resource. Must be an instance of a Resource class such as ``TableResource``, ``DatabaseResource``, ``QueryResource``, or ``InstanceResource``.
``actor`` - dictionary, optional
The authenticated actor. This is usually ``request.actor``. Defaults to ``None`` for unauthenticated requests.
This method checks if the given actor has permission to perform the given action on the given resource. All parameters must be passed as keyword arguments.
This method uses :ref:`datasette_allowed_resources_sql` under the hood and is an efficient way to list the databases, tables or other resources that an actor can access for a specific action.
Builds the SQL query that Datasette uses to determine which resources an actor may access for a specific action. Returns a ``(sql: str, params: dict)`` namedtuple that can be executed against the internal ``catalog_*`` database tables. ``parent`` can be used to limit results to a specific database, and ``include_is_private`` adds a column indicating whether anonymous users would be denied access to that resource.
Plugins that need to execute custom analysis over the raw allow/deny rules can use this helper to run the same query that powers the ``/-/allowed`` debugging interface.
The SQL query built by this method will return the following columns:
-``parent``: The parent resource identifier (or NULL)
-``child``: The child resource identifier (or NULL)
-``reason``: The reason from the rule that granted access
The resource to check the permission against. Must be an instance of ``InstanceResource``, ``DatabaseResource``, or ``TableResource`` from the ``datasette.resources`` module. If omitted, defaults to ``InstanceResource()`` for instance-level permissions.
The authenticated actor. This is usually ``request.actor``.
This is a convenience wrapper around :ref:`datasette_allowed` that raises a ``datasette.Forbidden`` exception if the permission check fails. Use this when you want to enforce a permission check and halt execution if the actor is not authorized.
The resource being checked, as a Resource object such as ``DatabaseResource(database=...)``, ``TableResource(database=..., table=...)``, or ``QueryResource(database=..., query=...)``. Only some permissions apply to a resource.
This convenience method can be used to answer the question "should this item be considered private, in that it is visible to me but it is not visible to anonymous users?"
It returns a tuple of two booleans, ``(visible, private)``. ``visible`` indicates if the actor can see this resource. ``private`` will be ``True`` if an anonymous user would not be able to view the resource.
This example checks if the user can access a specific table, and sets ``private`` so that a padlock icon can later be displayed:
This is an ``async`` method that returns an :ref:`API token <CreateTokenView>` string which can be used to authenticate requests to the Datasette API. The default ``SignedTokenHandler`` returns tokens of the format ``dstok_...``.
All tokens must have an ``actor_id`` string indicating the ID of the actor which the token will act on behalf of.
Tokens default to lasting forever, but can be set to expire after a given number of seconds using the ``expires_after`` argument. The following code creates a token for ``user1`` that will expire after an hour:
-``allow_resource(database, resource, action)`` - allow an action on a specific resource (table, SQL view or :ref:`stored query <stored_queries>`) within a database
``TokenRestrictions`` also provides an ``abbreviated(datasette)`` method which returns the restrictions as a dictionary using the compact format described in :ref:`authentication_cli_create_token_restrict`, with action names replaced by their registered abbreviations. It returns the inner dictionary only - the ``"_r"`` wrapping key shown in that section is not included. Returns ``None`` if no restrictions are set. This is useful when writing a custom :ref:`plugin_hook_register_token_handler` that needs to embed restrictions in a token payload.
The following example creates a token that can access ``view-instance`` and ``view-table`` across everything, can additionally use ``view-query`` for anything in the ``docs`` database and is allowed to execute ``insert-row`` and ``update-row`` in the ``attachments`` table in that database:
This is an ``async`` method that verifies an API token by trying each registered token handler in order. Returns an actor dictionary from the first handler that recognizes the token, or ``None`` if no handler accepts it.
Returns the specified database object. Raises a ``KeyError`` if the database does not exist. Call this method without an argument to return the first connected database.
Metadata about the instance, databases, tables and columns is stored in tables in :ref:`internals_internal`. The following methods are the supported API for plugins to read and update that stored metadata.
:ref:`Stored queries <stored_queries>` are stored in the ``queries`` table in the :ref:`internal database <internals_internal>`. Plugins can use the following methods to add, update, list and remove stored queries.
.._datasette_add_query:
await .add_query(database, name, sql, ...)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Adds a stored query.
..code-block:: python
async def add_query(
self,
database,
name,
sql,
*,
title=None,
description=None,
description_html=None,
hide_sql=False,
fragment=None,
parameters=None,
is_write=False,
is_private=False,
is_trusted=False,
source="plugin",
owner_id=None,
on_success_message=None,
on_success_message_sql=None,
on_success_redirect=None,
on_error_message=None,
on_error_redirect=None,
replace=True,
): ...
``database`` - string
The name of the database this query should belong to.
``name`` - string
The name of the stored query, used in the URL for that query.
``sql`` - string
The SQL for the stored query.
``title`` - string, optional
A display title for the query.
``description`` - string, optional
A plain text description.
``description_html`` - string, optional
An HTML description.
``hide_sql`` - boolean, optional
Set to ``True`` to hide the SQL by default on the query page.
``fragment`` - string, optional
A URL fragment to append to query links, for example ``"chart"``.
``parameters`` - list of strings, optional
Explicit parameter names for the query form. If omitted, Datasette derives parameters from the SQL.
``is_write`` - boolean, optional
Set to ``True`` for writable queries. They will the run against the SQLite write connection for the database.
``is_private`` - boolean, optional
Set to ``True`` for private queries. Private queries can only be viewed, updated or deleted by their owner.
``is_trusted`` - boolean, optional
Set to ``True`` for :ref:`trusted stored queries <trusted_stored_queries>`.
``source`` - string, optional
Identifies where the query came from. Defaults to ``"plugin"``.
``owner_id`` - string, optional
Actor ID of the query owner, used by private query permissions.
Options for :ref:`writable queries <queries_writable>`.
``replace`` - boolean, optional
Defaults to ``True``, which replaces any existing stored query with the same ``database`` and ``name``. Set this to ``False`` to raise a SQLite integrity error if the query already exists.
Example:
..code-block:: python
await datasette.add_query(
database="fixtures",
name="recent_rows",
sql="select * from facetable order by created desc limit 10",
title="Recent rows",
source="my-plugin",
)
.._datasette_update_query:
await .update_query(database, name, ...)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Updates fields for an existing stored query. Only keyword arguments that are provided will be changed.
The available keyword arguments are the same as those for :ref:`datasette_add_query`, except for ``replace``. Pass ``None`` to clear optional text fields and options such as ``on_success_redirect``. Passing ``hide_sql=False`` removes the ``hide_sql`` option.
Pagination cursor for the next page, if one exists.
``has_more`` - boolean
``True`` if another page of results is available.
``limit`` - integer
The limit used for this page.
.._datasette_count_queries:
await .count_queries(database=None, ...)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Counts stored queries visible to the specified actor. This accepts the same filtering keyword arguments as :ref:`datasette_list_queries`, except for ``limit``, ``cursor`` and ``include_private``.
.._datasette_remove_query:
await .remove_query(database, name, source=None)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Removes a stored query.
``database`` - string
The database the query belongs to.
``name`` - string
The query name.
``source`` - string, optional
If provided, only a query with this source will be removed.
Column types are stored in the ``column_types`` table in the :ref:`internal database <internals_internal>`. The following methods provide the API for reading and modifying column type assignments.
Returns a dictionary mapping column names to ``ColumnType`` subclass instances (with ``.config`` populated) for all columns that have assigned types on the given resource.
``.add_database()`` returns the Database instance, with its name set as the ``database.name`` attribute. Any time you are working with a newly added database you should use the return value of ``.add_database()``, for example:
Release all resources held by this ``Datasette`` instance. This calls :ref:`database_close` on every attached database (including the internal database), shuts down the thread pool executor used to run SQL queries, and unlinks the temporary file used to back the internal database if one was created.
``close()`` is synchronous, idempotent and one-way: after a call to ``close()`` any attempt to use the Datasette instance to execute SQL will raise a ``datasette.database.DatasetteClosedError`` exception. A closed ``Datasette`` cannot be reopened — callers that need a fresh instance should construct a new one.
If a call to ``Database.close()`` on one of the attached databases raises an exception, ``Datasette.close()`` will continue trying to close the remaining databases and will re-raise the first exception after every database has been processed.
When Datasette is being served over ASGI the ``close()`` method is wired up to the lifespan shutdown event, so resources are released cleanly on ``SIGTERM`` / ``SIGINT``.
An alternative namespace, see the `itsdangerous salt documentation <https://itsdangerous.palletsprojects.com/en/1.1.x/serializer/#the-salt>`__.
Utility method for signing values, such that you can safely pass data to and from an untrusted environment. This is a wrapper around the `itsdangerous <https://itsdangerous.palletsprojects.com/>`__ library.
This method returns a signed string, which can be decoded and verified using :ref:`datasette_unsign`.
.._datasette_unsign:
.unsign(value, namespace="default")
-----------------------------------
``signed`` - any serializable type
The signed string that was created using :ref:`datasette_sign`.
``namespace`` - string, optional
The alternative namespace, if one was used.
Returns the original, decoded object that was passed to :ref:`datasette_sign`. If the signature is not valid this raises a ``itsdangerous.BadSignature`` exception.
The message type - ``datasette.INFO``, ``datasette.WARNING`` or ``datasette.ERROR``
Datasette's flash messaging mechanism allows you to add a message that will be displayed to the user on the next page that they visit. Messages are persisted in a ``ds_messages`` cookie. This method adds a message to that cookie.
You can try out these messages (including the different visual styling of the three message types) using the ``/-/messages`` debugging tool.
The current request object is used to determine the hostname and protocol that should be used for the returned URL. The :ref:`setting_force_https_urls` configuration setting is taken into account.
If you are implementing your own custom views, you may need to resolve the database that the user is requesting based on a URL path. If the regular expression for your route declares a ``database`` named group, you can use this method to resolve the database object.
This returns a :ref:`Database <internals_database>` instance.
If the database cannot be found, it raises a ``datasette.utils.asgi.DatabaseNotFound`` exception - which is a subclass of ``datasette.utils.asgi.NotFound`` with a ``.database_name`` attribute set to the name of the database that was requested.
.._datasette_resolve_table:
.resolve_table(request)
-----------------------
``request`` - :ref:`internals_request`
A request object
This assumes that the regular expression for your route declares both a ``database`` and a ``table`` named group.
It returns a ``ResolvedTable`` named tuple instance with the following fields:
``db`` - :ref:`Database <internals_database>`
The database object
``table`` - string
The name of the table (or view)
``is_view`` - boolean
``True`` if this is a view, ``False`` if it is a table
If the database or table cannot be found it raises a ``datasette.utils.asgi.DatabaseNotFound`` exception.
If the table does not exist it raises a ``datasette.utils.asgi.TableNotFound`` exception - a subclass of ``datasette.utils.asgi.NotFound`` with ``.database_name`` and ``.table`` attributes.
.._datasette_resolve_row:
.resolve_row(request)
---------------------
``request`` - :ref:`internals_request`
A request object
This method assumes your route declares named groups for ``database``, ``table`` and ``pks``.
It returns a ``ResolvedRow`` named tuple instance with the following fields:
``db`` - :ref:`Database <internals_database>`
The database object
``table`` - string
The name of the table
``sql`` - string
SQL snippet that can be used in a ``WHERE`` clause to select the row
``params`` - dict
Parameters that should be passed to the SQL query
``pks`` - list
List of primary key column names
``pk_values`` - list
List of primary key values decoded from the URL
``row`` - ``sqlite3.Row``
The row itself
If the database or table cannot be found it raises a ``datasette.utils.asgi.DatabaseNotFound`` exception.
If the table does not exist it raises a ``datasette.utils.asgi.TableNotFound`` exception.
If the row cannot be found it raises a ``datasette.utils.asgi.RowNotFound`` exception. This has ``.database_name``, ``.table`` and ``.pk_values`` attributes, extracted from the request path.
Plugins can make internal simulated HTTP requests to the Datasette instance within which they are running. This ensures that all of Datasette's external JSON APIs are also available to plugins, while avoiding the overhead of making an external HTTP call to access those APIs.
The ``datasette.client`` object is a wrapper around the `HTTPX Python library <https://www.python-httpx.org/>`__, providing an async-friendly API that is similar to the widely used `Requests library <https://requests.readthedocs.io/>`__.
``datasette.client`` methods automatically take the current :ref:`setting_base_url` setting into account, whether or not you use the ``datasette.urls`` family of methods to construct the path.
For documentation on available ``**kwargs`` options and the shape of the HTTPX Response object refer to the `HTTPX Async documentation <https://www.python-httpx.org/async/>`__.
All ``datasette.client`` methods accept an optional ``actor=`` parameter. When set to a dictionary describing an actor, the request is made with a signed ``ds_actor`` cookie identifying that actor — as if the request had been made by a user who is signed in as that actor.
This is a convenient shorthand equivalent to signing the cookie manually using ``datasette.client.actor_cookie()``.
This parameter works with all HTTP methods (``get``, ``post``, ``put``, ``patch``, ``delete``, ``options``, ``head``) and the generic ``request`` method.
Passing both ``actor=`` and a ``ds_actor`` cookie via ``cookies=`` raises a ``TypeError``. Other unrelated cookies can be combined with ``actor=``.
All ``datasette.client`` methods accept an optional ``skip_permission_checks=True`` parameter. When set, all permission checks will be bypassed for that request, allowing access to any resource regardless of the configured permissions.
This is useful for plugins and internal operations that need to access all resources without being subject to permission restrictions.
Example usage:
..code-block:: python
# Regular request - respects permissions
response = await datasette.client.get(
"/private-db/secret-table.json"
)
# May return 403 Forbidden if access is denied
# With skip_permission_checks - bypasses all permission checks
response = await datasette.client.get(
"/private-db/secret-table.json",
skip_permission_checks=True,
)
# Will return 200 OK and the data, regardless of permissions
This parameter works with all HTTP methods (``get``, ``post``, ``put``, ``patch``, ``delete``, ``options``, ``head``) and the generic ``request`` method.
..warning::
Use ``skip_permission_checks=True`` with caution. It completely bypasses Datasette's permission system and should only be used in trusted plugin code or internal operations where you need guaranteed access to resources.
Returns ``True`` if the current code is executing within a ``datasette.client`` request, ``False`` otherwise.
This method is useful for plugins that need to behave differently when called through ``datasette.client`` versus when handling external HTTP requests.
Note that ``datasette.in_client()`` is independent of ``skip_permission_checks``. A request made through ``datasette.client`` will always have ``in_client()`` return ``True``, regardless of whether ``skip_permission_checks`` is set.
The ``datasette.urls`` object contains methods for building URLs to pages within Datasette. Plugins should use this to link to pages, since these methods take into account any :ref:`setting_base_url` configuration setting that might be in effect.
Takes a path and returns the full path, taking ``base_url`` into account.
For example, ``datasette.urls.path("-/logout")`` will return the path to the logout page, which will be ``"/-/logout"`` by default or ``/prefix-path/-/logout`` if ``base_url`` is set to ``/prefix-path/``
``datasette.urls.static_plugins("datasette_cluster_map", "datasette-cluster-map.js")`` would return ``"/-/static-plugins/datasette_cluster_map/datasette-cluster-map.js"``
Use the ``format="json"`` (or ``"csv"`` or other formats supported by plugins) arguments to get back URLs to the JSON representation. This is the path with ``.json`` added on the end.
These methods each return a ``datasette.utils.PrefixedUrlString`` object, which is a subclass of the Python ``str`` type. This allows the logic that considers the ``base_url`` setting to detect if that prefix has already been applied to the path.
The ``PermissionSQL`` class is used by plugins to contribute SQL-based permission rules through the :ref:`plugin_hook_permission_resources_sql` hook. This enables efficient permission checking across multiple resources by leveraging SQLite's query engine.
When multiple ``PermissionSQL`` objects return conflicting rules for the same resource, Datasette applies the following precedence:
1.**Specificity**: Child-level rules (with both ``parent`` and ``child``) override parent-level rules (with only ``parent``), which override root-level rules (with neither ``parent`` nor ``child``)
2.**Deny over allow**: At the same specificity level, deny (``allow=0``) takes precedence over allow (``allow=1``)
3.**Implicit deny**: If no rules match a resource, access is denied by default
Use this to create a named in-memory database. Unlike regular memory databases these can be accessed by multiple threads and will persist an changes made to them for the lifetime of the Datasette server process.
Set this to ``True`` to create a temporary file-backed database. This creates a SQLite database in a temporary file on disk (using Python's ``tempfile.mkstemp()``) with WAL mode enabled for better concurrent read/write performance. The temporary file is automatically cleaned up when the database is closed or when the process exits.
Unlike named in-memory databases (``memory_name``), temporary disk databases support concurrent readers and writers without locking errors, because WAL mode allows readers and writers to operate simultaneously. This makes them suitable for use cases like the internal database where concurrent access is common.
When ``is_temp_disk=True``, the ``path``, ``is_mutable``, and ``mode`` parameters are set automatically and should not be provided.
The first argument is the ``datasette`` instance you are attaching to, the second is a ``path=``, then ``is_mutable`` and ``is_memory`` are both optional arguments.
If the database was opened in immutable mode, this property returns the 64 character SHA-256 hash of the database contents as a string. Otherwise it returns ``None``.
Executes a SQL query against the database and returns the resulting rows (see :ref:`database_results`).
``sql`` - string (required)
The SQL query to execute. This can include ``?`` or ``:named`` parameters.
``params`` - list or dict
A list or dictionary of values to use for the parameters. List for ``?``, dictionary for ``:named``.
``truncate`` - boolean
Should the rows returned by the query be truncated at the maximum page size? Defaults to ``True``, set this to ``False`` to disable truncation.
``custom_time_limit`` - integer ms
A custom time limit for this query. This can be set to a lower value than the Datasette configured default. If a query takes longer than this it will be terminated early and raise a ``dataette.database.QueryInterrupted`` exception.
``page_size`` - integer
Set a custom page size for truncation, over-riding the configured Datasette default.
``log_sql_errors`` - boolean
Should any SQL errors be logged to the console in addition to being raised as an error? Defaults to ``True``.
.._database_results:
Results
-------
The ``db.execute()`` method returns a single ``Results`` object. This can be used to access the rows returned by the query.
Iterating over a ``Results`` object will yield SQLite `Row objects <https://docs.python.org/3/library/sqlite3.html#row-objects>`__. Each of these can be treated as a tuple or can be accessed using ``row["column"]`` syntax:
..code-block:: python
info = []
results = await db.execute("select name from sqlite_master")
for row in results:
info.append(row["name"])
The ``Results`` object also has the following properties and methods:
``.truncated`` - boolean
Indicates if this query was truncated - if it returned more results than the specified ``page_size``. If this is true then the results object will only provide access to the first ``page_size`` rows in the query result. You can disable truncation by passing ``truncate=False`` to the ``db.query()`` method.
Returns the first row in the results, or ``None`` if no rows were returned.
``.single_value()``
Returns the value of the first column of the first row of results - but only if the query returned a single row with a single column. Raises a ``datasette.database.MultipleValues`` exception otherwise.
``.__len__()``
Calling ``len(results)`` returns the (truncated) number of returned results.
Executes a given callback function against a read-only database connection running in a thread. The function will be passed a SQLite connection, and the return value from the function will be returned by the ``await``.
SQLite only allows one database connection to write at a time. Datasette handles this for you by maintaining a queue of writes to be executed against a given database. Plugins can submit write operations to this queue and they will be executed in the order in which they are received.
The method will block until the operation is completed, and the return value will be the return from calling ``conn.execute(...)`` using the underlying ``sqlite3`` Python library.
If you pass ``block=False`` this behavior changes to "fire and forget" - queries will be added to the write queue and executed in a separate thread while your code can continue to do other things. The method will return a UUID representing the queued task.
Each call to ``execute_write()`` will be executed inside a transaction.
Like ``execute_write()`` but can be used to send multiple SQL statements in a single string separated by semicolons, using the ``sqlite3```conn.executescript() <https://docs.python.org/3/library/sqlite3.html#sqlite3.Cursor.executescript>`__ method.
Like ``execute_write()`` but uses the ``sqlite3```conn.executemany() <https://docs.python.org/3/library/sqlite3.html#sqlite3.Cursor.executemany>`__ method. This will efficiently execute the same SQL statement against each of the parameters in the ``params_seq`` iterator, for example:
..code-block:: python
await db.execute_write_many(
"insert into characters (id, name) values (?, ?)",
This method works like ``.execute_write()``, but instead of a SQL statement you give it a callable Python function. Your function will be queued up and then called when the write connection is available, passing that connection as the argument to the function.
The function can then perform multiple actions, safe in the knowledge that it has exclusive access to the single writable connection for as long as it is executing.
Your function can optionally accept a ``track_event`` parameter in addition to ``conn``. If it does, it will be passed a callable that can be used to queue events for dispatch after the write transaction commits successfully. Events queued this way are discarded if the write raises an exception.
..code-block:: python
from datasette.events import AlterTableEvent
def my_write(conn, track_event):
before_schema = conn.execute(
"select sql from sqlite_master where name = 'my_table'"
).fetchone()[0]
conn.execute(
"alter table my_table add column new_col text"
)
after_schema = conn.execute(
"select sql from sqlite_master where name = 'my_table'"
By default your function will be executed inside a transaction. You can pass ``transaction=False`` to disable this behavior, though if you do that you should be careful to manually apply transactions - ideally using the ``with conn:`` pattern, or you may see ``OperationalError: database table is locked`` errors.
If you specify ``block=False`` the method becomes fire-and-forget, queueing your function to be executed and then allowing your code after the call to ``.execute_write_fn()`` to continue running while the underlying thread waits for an opportunity to run your function. A UUID representing the queued task will be returned. Any exceptions in your code will be silently swallowed.
This method works is similar to :ref:`execute_write_fn() <database_execute_write_fn>` but executes the provided function in an entirely isolated SQLite connection, which is opened, used and then closed again in a single call to this method.
The :ref:`prepare_connection() <plugin_hook_prepare_connection>` plugin hook is not executed against this connection.
This allows plugins to execute database operations that might conflict with how database connections are usually configured. For example, running a ``VACUUM`` operation while bypassing any restrictions placed by the `datasette-sqlite-authorizer <https://github.com/datasette/datasette-sqlite-authorizer>`__ plugin.
Running ``VACUUM`` using this method also ensures it won't trigger incorrect :class:`~datasette.events.RenameTableEvent` events, since ``execute_isolated_fn()`` does not trigger the Datasette mechanism that detects renamed tables in a way that can be confused by a ``VACUUM``.
Plugins can also use this method to load potentially dangerous SQLite extensions, use them to perform an operation and then have them safely unloaded at the end of the call, without risk of exposing them to other connections.
Functions run using ``execute_isolated_fn()`` share the same queue as ``execute_write_fn()``, which guarantees that no writes can be executed at the same time as the isolated function is executing.
The return value of the function will be returned by this method. Any exceptions raised by the function will be raised out of the ``await`` line as well.
Release all resources held by this ``Database`` instance. This shuts down the background write thread (if one was started by a previous call to :ref:`database_execute_write_fn` or similar), closes the write connection, and closes any cached read connections.
After ``db.close()`` has been called, any further call to :ref:`database_execute`, :ref:`database_execute_fn`, :ref:`database_execute_write`, :ref:`database_execute_write_fn`, :ref:`database_execute_write_many`, :ref:`database_execute_write_script` or :ref:`database_execute_isolated_fn` will raise a ``datasette.database.DatasetteClosedError`` exception.
``close()`` is idempotent — calling it a second time is a no-op. It is one-way: a closed ``Database`` cannot be reopened.
Is this database a temporary file-backed database? See :ref:`database_constructor` for details. Temporary disk databases report ``hash`` as ``None`` but have real values for ``size`` and ``mtime_ns`` since they are backed by a file on disk.
``await db.attached_databases()`` - list of named tuples
Returns a list of additional databases that have been connected to this database using the SQLite ATTACH command. Each named tuple has fields ``seq``, ``name`` and ``file``.
``await db.table_column_details(table)`` - list of named tuples
Full details of the columns in a specific table. Each column is represented by a ``Column`` named tuple with fields ``cid`` (integer representing the column position), ``name`` (string), ``type`` (string, e.g. ``REAL`` or ``VARCHAR(30)``), ``notnull`` (integer 1 or 0), ``default_value`` (string or None), ``is_pk`` (integer 1 or 0).
The label column that is associated with this table - either automatically detected or using the ``"label_column"`` key in configuration, see :ref:`table_configuration_label_column`.
``await db.foreign_keys_for_table(table)`` - list of dictionaries
Details of columns in this table which are foreign keys to other tables. A list of dictionaries where each dictionary is shaped like this: ``{"column": string, "other_table": string, "other_column": string}``.
``await db.hidden_table_names()`` - list of strings
List of tables which Datasette "hides" by default - usually these are tables associated with SQLite's full-text search feature, the SpatiaLite extension or tables hidden using the :ref:`table_configuration_hidden` feature.
Dictionary representing both incoming and outgoing foreign keys for every table in this database. Each key is a table name that points to a dictionary with two keys, ``"incoming"`` and ``"outgoing"``, each of which is a list of dictionaries with keys ``"column"``, ``"other_table"`` and ``"other_column"``. For example:
Datasette protects against Cross-Site Request Forgery by inspecting the browser-set ``Sec-Fetch-Site`` and ``Origin`` headers on every unsafe (non-``GET``/``HEAD``/``OPTIONS``) request, following the approach described in `Filippo Valsorda's article <https://words.filippo.io/csrf/>`__ and implemented in Go 1.25's ``http.CrossOriginProtection``.
Requests from non-browser clients (``curl``, server-to-server scripts, etc.) do not send ``Sec-Fetch-Site`` or ``Origin`` and pass through unchanged - CSRF is a browser-only attack.
No token, cookie, or hidden form field is needed. Any ``<form method="POST">`` inside Datasette or a plugin will be accepted from the same origin without modification.
Datasette maintains an "internal" SQLite database used for configuration, caching, and storage. Plugins can store configuration, settings, and other data inside this database. By default, Datasette will use a temporary in-memory SQLite database as the internal database, which is created at startup and destroyed at shutdown. Users of Datasette can optionally pass in a ``--internal`` flag to specify the path to a SQLite database to use as the internal database, which will persist internal data across Datasette instances.
Datasette maintains tables called ``catalog_databases``, ``catalog_tables``, ``catalog_views``, ``catalog_columns``, ``catalog_indexes``, ``catalog_foreign_keys`` with details of the attached databases and their schemas. These tables should not be considered a stable API - they may change between Datasette releases.
Metadata is stored in tables ``metadata_instance``, ``metadata_databases``, ``metadata_resources`` and ``metadata_columns``. Plugins can interact with these tables via the :ref:`get_*_metadata() and set_*_metadata() methods <datasette_get_set_metadata>`.
The internal database is not exposed in the Datasette application by default, which means private data can safely be stored without worry of accidentally leaking information through the default Datasette interface and API. However, other plugins do have full read and write access to the internal database.
Plugins can access this database by calling ``internal_db = datasette.get_internal_database()`` and then executing queries using the :ref:`Database API <internals_database>`.
1. Use a unique prefix when creating tables, indices, and triggers in the internal database. If your plugin is called ``datasette-xyz``, then prefix names with ``datasette_xyz_*``.
The ``datasette.utils`` module contains various utility functions used by Datasette. As a general rule you should consider anything in this module to be unstable - functions and classes here could change without warning or be removed entirely between Datasette releases, without being mentioned in the release notes.
The exception to this rule is anything that is documented here. If you find a need for an undocumented utility function in your own work, consider `opening an issue <https://github.com/simonw/datasette/issues/new>`__ requesting that the function you are using be upgraded to documented and supported status.
This function accepts a string containing either JSON or YAML, expected to be of the format described in :ref:`metadata`. It returns a nested Python dictionary representing the parsed data from that string.
If the metadata cannot be parsed as either JSON or YAML the function will raise a ``utils.BadMetadataError`` exception.
Utility function for calling ``await`` on a return value if it is awaitable, otherwise returning the value. This is used by Datasette to support plugin hooks that can optionally return awaitable functions. Read more about this function in `The “await me maybe” pattern for Python asyncio <https://simonwillison.net/2020/Sep/2/await-me-maybe/>`__.
Datasette uses a custom encoding scheme in some places, called **tilde encoding**. This is primarily used for table names and row primary keys, to avoid any confusion between ``/`` characters in those values and the Datasette URLs that reference them.
Tilde encoding uses the same algorithm as `URL percent-encoding <https://developer.mozilla.org/en-US/docs/Glossary/percent-encoding>`__, but with the ``~`` tilde character used in place of ``%``.
Any character other than ``ABCDEFGHIJKLMNOPQRSTUVWXYZ abcdefghijklmnopqrstuvwxyz0123456789_-`` will be replaced by the numeric equivalent preceded by a tilde. For example:
Call ``fn``, passing it only those keyword arguments that match its function signature. This implements a dependency injection pattern - the caller provides all available arguments, and the function receives only the ones it declares as parameters.
This is useful in plugins that want to define callback functions that only declare the arguments they need. For example:
..code-block:: python
from datasette.utils import call_with_supported_arguments
def my_callback(request, datasette): ...
# This will pass only request and datasette, ignoring other kwargs:
Running Datasette with ``--setting trace_debug 1`` enables trace debug output, which can then be viewed by adding ``?_trace=1`` to the query string for any page.
You can see an example of this at the bottom of `latest.datasette.io/fixtures/facetable?_trace=1 <https://latest.datasette.io/fixtures/facetable?_trace=1>`__. The JSON output shows full details of every SQL query that was executed to generate the page.
The `datasette-pretty-traces <https://datasette.io/plugins/datasette-pretty-traces>`__ plugin can be installed to provide a more readable display of this information. You can see `a demo of that here <https://latest-with-plugins.datasette.io/github/commits?_trace=1>`__.
You can add your own custom traces to the JSON output using the ``trace()`` context manager. This takes a string that identifies the type of trace being recorded, and records any keyword arguments as additional JSON keys on the resulting trace object.
The start and end time, duration and a traceback of where the trace was executed will be automatically attached to the JSON object.
This example uses trace to record the start, end and duration of any HTTP GET requests made using the function:
If your code uses a mechanism such as ``asyncio.gather()`` to execute code in additional tasks you may find that some of the traces are missing from the display.
You can use the ``trace_child_tasks()`` context manager to ensure these child tasks are correctly handled.
..code-block:: python
from datasette import tracer
with tracer.trace_child_tasks():
results = await asyncio.gather(
# ... async tasks here
)
This example uses the :ref:`register_routes() <plugin_register_routes>` plugin hook to add a page at ``/parallel-queries`` which executes two SQL queries in parallel using ``asyncio.gather()`` and returns their results.
Note that running parallel SQL queries in this way has `been known to cause problems in the past <https://github.com/simonw/datasette/issues/2189>`__, so treat this example with caution.
