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``.
``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.
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.
The dictionary keys are the permission names - e.g. ``view-instance`` - and the values are ``Permission()`` objects describing the permission. Here is a :ref:`description of that object <plugin_register_permissions>`.
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 resource, e.g. the name of the database, or a tuple of two strings containing the name of the database and the name of the table. Only some permissions apply to a resource.
Some permission checks are carried out against :ref:`rules defined in datasette.yaml <authentication_permissions_config>`, while other custom permissions may be decided by plugins that implement the :ref:`plugin_hook_permission_allowed` plugin hook.
This method allows multiple permissions to be checked at once. It raises a ``datasette.Forbidden`` exception if any of the checks are denied before one of them is explicitly granted.
This is useful when you need to check multiple permissions at once. For example, an actor should be able to view a table if either one of the following checks returns ``True`` or not a single one of them returns ``False``:
The name of the action that is being permission checked.
``resource`` - string or tuple, optional
The resource, e.g. the name of the database, or a tuple of two strings containing the name of the database and the name of the table. 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:
The following example runs three checks in a row, similar to :ref:`datasette_ensure_permissions`. If any of the checks are denied before one of them is explicitly granted then ``visible`` will be ``False``. ``private`` will be ``True`` if an anonymous user would not be able to view the resource.
The number of seconds after which the token should expire.
``restrict_all`` - iterable, optional
A list of actions that this token should be restricted to across all databases and resources.
``restrict_database`` - dict, optional
For restricting actions within specific databases, e.g. ``{"mydb": ["view-table", "view-query"]}``.
``restrict_resource`` - dict, optional
For restricting actions to specific resources (tables, SQL views and :ref:`canned_queries`) within a database. For example: ``{"mydb": {"mytable": ["insert-row", "update-row"]}}``.
This method returns a signed :ref:`API token <CreateTokenView>` of the format ``dstok_...`` which can be used to authenticate requests to the Datasette API.
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:
..code-block:: python
token = datasette.create_token(
actor_id="user1",
expires_after=3600,
)
The three ``restrict_*`` arguments can be used to create a token that has additional restrictions beyond what the associated actor is allowed to do.
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:
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.
``.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:
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/>`__.
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.
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.
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.
This property provides direct access to the list of rows returned by the database. You can access specific rows by index using ``results.rows[0]``.
``.first()`` - row or None
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.
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.
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.
Closes all of the open connections to file-backed databases. This is mainly intended to be used by large test suites, to avoid hitting limits on the number of open files.
``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).
``await db.primary_keys(table)`` - list of strings
Names of the columns that are part of the primary key for this table.
``await db.fts_table(table)`` - string or None
The name of the FTS table associated with this table, if one exists.
``await db.label_column_for_table(table)`` - string or None
The label column that is associated with this table - either automatically detected or using the ``"label_column"`` key from :ref:`metadata`, see :ref:`label_columns`.
``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:`metadata_hiding_tables` feature.
``await db.get_table_definition(table)`` - string
Returns the SQL definition for the table - the ``CREATE TABLE`` statement and any associated ``CREATE INDEX`` statements.
``await db.get_view_definition(view)`` - string
Returns the SQL definition of the named view.
``await db.get_all_foreign_keys()`` - dictionary
Dictionary representing both incoming and outgoing foreign keys for this table. It has two keys, ``"incoming"`` and ``"outgoing"``, each of which is a list of dictionaries with keys ``"column"``, ``"other_table"`` and ``"other_column"``. For example:
Datasette uses `asgi-csrf <https://github.com/simonw/asgi-csrf>`__ to guard against CSRF attacks on form POST submissions. Users receive a ``ds_csrftoken`` cookie which is compared against the ``csrftoken`` form field (or ``x-csrftoken`` HTTP header) for every incoming request.
If your plugin implements a ``<form method="POST">`` anywhere you will need to include that token. You can do so with the following template snippet:
If you are rendering templates using the :ref:`datasette_render_template` method the ``csrftoken()`` helper will only work if you provide the ``request=`` argument to that method. If you forget to do this you will see the following error::
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_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.
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:
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.