.. _type_hints-example:

Type Hints
==========

As of version 4.1, PyMongo ships with `type hints`_. With type hints, Python
type checkers can easily find bugs before they reveal themselves in your code.

If your IDE is configured to use type hints,
it can suggest more appropriate completions and highlight errors in your code.
Some examples include `PyCharm`_,  `Sublime Text`_, and `Visual Studio Code`_.

You can also use the `mypy`_ tool from your command line or in Continuous Integration tests.

All of the public APIs in PyMongo are fully type hinted, and
several of them support generic parameters for the
type of document object returned when decoding BSON documents.

Due to `limitations in mypy`_, the default
values for generic document types are not yet provided (they will eventually be ``Dict[str, any]``).

For a larger set of examples that use types, see the PyMongo `test_typing module`_.

If you would like to opt out of using the provided types, add the following to
your `mypy config`_: ::

    [mypy-pymongo]
    follow_imports = False


Basic Usage
-----------

Note that a type for :class:`~pymongo.mongo_client.MongoClient` must be specified.  Here we use the
default, unspecified document type:

.. doctest::

  >>> from pymongo import MongoClient
  >>> client: MongoClient = MongoClient()
  >>> collection = client.test.test
  >>> inserted = collection.insert_one({"x": 1, "tags": ["dog", "cat"]})
  >>> retrieved = collection.find_one({"x": 1})
  >>> assert isinstance(retrieved, dict)

For a more accurate typing for document type you can use:

.. doctest::

  >>> from typing import Any, Dict
  >>> from pymongo import MongoClient
  >>> client: MongoClient[Dict[str, Any]] = MongoClient()
  >>> collection = client.test.test
  >>> inserted = collection.insert_one({"x": 1, "tags": ["dog", "cat"]})
  >>> retrieved = collection.find_one({"x": 1})
  >>> assert isinstance(retrieved, dict)

Typed Client
------------

:class:`~pymongo.mongo_client.MongoClient` is generic on the document type used to decode BSON documents.

You can specify a :class:`~bson.raw_bson.RawBSONDocument` document type:

.. doctest::

  >>> from pymongo import MongoClient
  >>> from bson.raw_bson import RawBSONDocument
  >>> client = MongoClient(document_class=RawBSONDocument)
  >>> collection = client.test.test
  >>> inserted = collection.insert_one({"x": 1, "tags": ["dog", "cat"]})
  >>> result = collection.find_one({"x": 1})
  >>> assert isinstance(result, RawBSONDocument)

Subclasses of :py:class:`collections.abc.Mapping` can also be used, such as :class:`~bson.son.SON`:

.. doctest::

  >>> from bson import SON
  >>> from pymongo import MongoClient
  >>> client = MongoClient(document_class=SON[str, int])
  >>> collection = client.test.test
  >>> inserted = collection.insert_one({"x": 1, "y": 2})
  >>> result = collection.find_one({"x": 1})
  >>> assert result is not None
  >>> assert result["x"] == 1

Note that when using :class:`~bson.son.SON`, the key and value types must be given, e.g. ``SON[str, Any]``.


Typed Collection
----------------

You can use :py:class:`~typing.TypedDict` (Python 3.8+) when using a well-defined schema for the data in a
:class:`~pymongo.collection.Collection`. Note that all `schema validation`_ for inserts and updates is done on the server.
These methods automatically add an "_id" field.

.. doctest::
  :pyversion: >= 3.8

  >>> from typing import TypedDict
  >>> from pymongo import MongoClient
  >>> from pymongo.collection import Collection
  >>> class Movie(TypedDict):
  ...     name: str
  ...     year: int
  ...
  >>> client: MongoClient = MongoClient()
  >>> collection: Collection[Movie] = client.test.test
  >>> inserted = collection.insert_one(Movie(name="Jurassic Park", year=1993))
  >>> result = collection.find_one({"name": "Jurassic Park"})
  >>> assert result is not None
  >>> assert result["year"] == 1993
  >>> # This will raise a type-checking error, despite being present, because it is added by PyMongo.
  >>> assert result["_id"]  # type:ignore[typeddict-item]

This same typing scheme works for all of the insert methods (:meth:`~pymongo.collection.Collection.insert_one`,
:meth:`~pymongo.collection.Collection.insert_many`, and :meth:`~pymongo.collection.Collection.bulk_write`).
For ``bulk_write`` both :class:`~pymongo.operations.InsertOne` and :class:`~pymongo.operations.ReplaceOne` operators are generic.

.. doctest::
  :pyversion: >= 3.8

  >>> from typing import TypedDict
  >>> from pymongo import MongoClient
  >>> from pymongo.operations import InsertOne
  >>> from pymongo.collection import Collection
  >>> client: MongoClient = MongoClient()
  >>> collection: Collection[Movie] = client.test.test
  >>> inserted = collection.bulk_write([InsertOne(Movie(name="Jurassic Park", year=1993))])
  >>> result = collection.find_one({"name": "Jurassic Park"})
  >>> assert result is not None
  >>> assert result["year"] == 1993
  >>> # This will raise a type-checking error, despite being present, because it is added by PyMongo.
  >>> assert result["_id"]  # type:ignore[typeddict-item]

Modeling Document Types with TypedDict
--------------------------------------

You can use :py:class:`~typing.TypedDict` (Python 3.8+) to model structured data.
As noted above, PyMongo will automatically add an ``_id`` field if it is not present. This also applies to TypedDict.
There are three approaches to this:

  1. Do not specify ``_id`` at all. It will be inserted automatically, and can be retrieved at run-time, but will yield a type-checking error unless explicitly ignored.

  2. Specify ``_id`` explicitly. This will mean that every instance of your custom TypedDict class will have to pass a value for ``_id``.

  3. Make use of :py:class:`~typing.NotRequired`. This has the flexibility of option 1, but with the ability to access the ``_id`` field without causing a type-checking error.

Note: to use :py:class:`~typing.TypedDict` and :py:class:`~typing.NotRequired` in earlier versions of Python (<3.8, <3.11), use the ``typing_extensions`` package.

.. doctest:: typed-dict-example
  :pyversion: >= 3.11

  >>> from typing import TypedDict, NotRequired
  >>> from pymongo import MongoClient
  >>> from pymongo.collection import Collection
  >>> from bson import ObjectId
  >>> class Movie(TypedDict):
  ...     name: str
  ...     year: int
  ...
  >>> class ExplicitMovie(TypedDict):
  ...     _id: ObjectId
  ...     name: str
  ...     year: int
  ...
  >>> class NotRequiredMovie(TypedDict):
  ...     _id: NotRequired[ObjectId]
  ...     name: str
  ...     year: int
  ...
  >>> client: MongoClient = MongoClient()
  >>> collection: Collection[Movie] = client.test.test
  >>> inserted = collection.insert_one(Movie(name="Jurassic Park", year=1993))
  >>> result = collection.find_one({"name": "Jurassic Park"})
  >>> assert result is not None
  >>> # This will yield a type-checking error, despite being present, because it is added by PyMongo.
  >>> assert result["_id"]  # type:ignore[typeddict-item]
  >>> collection: Collection[ExplicitMovie] = client.test.test
  >>> # Note that the _id keyword argument must be supplied
  >>> inserted = collection.insert_one(
  ...     ExplicitMovie(_id=ObjectId(), name="Jurassic Park", year=1993)
  ... )
  >>> result = collection.find_one({"name": "Jurassic Park"})
  >>> assert result is not None
  >>> # This will not raise a type-checking error.
  >>> assert result["_id"]
  >>> collection: Collection[NotRequiredMovie] = client.test.test
  >>> # Note the lack of _id, similar to the first example
  >>> inserted = collection.insert_one(NotRequiredMovie(name="Jurassic Park", year=1993))
  >>> result = collection.find_one({"name": "Jurassic Park"})
  >>> assert result is not None
  >>> # This will not raise a type-checking error, despite not being provided explicitly.
  >>> assert result["_id"]


Typed Database
--------------

While less common, you could specify that the documents in an entire database
match a well-defined schema using :py:class:`~typing.TypedDict` (Python 3.8+).


.. doctest::

  >>> from typing import TypedDict
  >>> from pymongo import MongoClient
  >>> from pymongo.database import Database
  >>> class Movie(TypedDict):
  ...     name: str
  ...     year: int
  ...
  >>> client: MongoClient = MongoClient()
  >>> db: Database[Movie] = client.test
  >>> collection = db.test
  >>> inserted = collection.insert_one({"name": "Jurassic Park", "year": 1993})
  >>> result = collection.find_one({"name": "Jurassic Park"})
  >>> assert result is not None
  >>> assert result["year"] == 1993

Typed Command
-------------
When using the :meth:`~pymongo.database.Database.command`, you can specify the document type by providing a custom :class:`~bson.codec_options.CodecOptions`:

.. doctest::

  >>> from pymongo import MongoClient
  >>> from bson.raw_bson import RawBSONDocument
  >>> from bson import CodecOptions
  >>> client: MongoClient = MongoClient()
  >>> options = CodecOptions(RawBSONDocument)
  >>> result = client.admin.command("ping", codec_options=options)
  >>> assert isinstance(result, RawBSONDocument)

Custom :py:class:`collections.abc.Mapping` subclasses and :py:class:`~typing.TypedDict` (Python 3.8+) are also supported.
For :py:class:`~typing.TypedDict`, use the form: ``options: CodecOptions[MyTypedDict] = CodecOptions(...)``.

Typed BSON Decoding
-------------------
You can specify the document type returned by :mod:`bson` decoding functions by providing :class:`~bson.codec_options.CodecOptions`:

.. doctest::

  >>> from typing import Any, Dict
  >>> from bson import CodecOptions, encode, decode
  >>> class MyDict(Dict[str, Any]):
  ...     def foo(self):
  ...         return "bar"
  ...
  >>> options = CodecOptions(document_class=MyDict)
  >>> doc = {"x": 1, "y": 2}
  >>> bsonbytes = encode(doc, codec_options=options)
  >>> rt_document = decode(bsonbytes, codec_options=options)
  >>> assert rt_document.foo() == "bar"

:class:`~bson.raw_bson.RawBSONDocument` and :py:class:`~typing.TypedDict` (Python 3.8+) are also supported.
For :py:class:`~typing.TypedDict`, use  the form: ``options: CodecOptions[MyTypedDict] = CodecOptions(...)``.


Troubleshooting
---------------

Client Type Annotation
~~~~~~~~~~~~~~~~~~~~~~
If you forget to add a type annotation for a :class:`~pymongo.mongo_client.MongoClient` object you may get the following ``mypy`` error::

  from pymongo import MongoClient
  client = MongoClient()  # error: Need type annotation for "client"

The solution is to annotate the type as ``client: MongoClient`` or ``client: MongoClient[Dict[str, Any]]``.  See `Basic Usage`_.

Incompatible Types
~~~~~~~~~~~~~~~~~~
If you use the generic form of :class:`~pymongo.mongo_client.MongoClient` you
may encounter a ``mypy`` error like::

  from pymongo import MongoClient

  client: MongoClient = MongoClient()
  client.test.test.insert_many(
      {"a": 1}
  )  # error: Dict entry 0 has incompatible type "str": "int";
     # expected "Mapping[str, Any]": "int"


The solution is to use ``client: MongoClient[Dict[str, Any]]`` as used in
`Basic Usage`_ .

Actual Type Errors
~~~~~~~~~~~~~~~~~~

Other times ``mypy`` will catch an actual error, like the following code::

    from pymongo import MongoClient
    from typing import Mapping
    client: MongoClient = MongoClient()
    client.test.test.insert_one(
        [{}]
    )  # error: Argument 1 to "insert_one" of "Collection" has
       # incompatible type "List[Dict[<nothing>, <nothing>]]";
       # expected "Mapping[str, Any]"

In this case the solution is to use ``insert_one({})``, passing a document instead of a list.

Another example is trying to set a value on a :class:`~bson.raw_bson.RawBSONDocument`, which is read-only.::

    from bson.raw_bson import RawBSONDocument
    from pymongo import MongoClient

    client = MongoClient(document_class=RawBSONDocument)
    coll = client.test.test
    doc = {"my": "doc"}
    coll.insert_one(doc)
    retrieved = coll.find_one({"_id": doc["_id"]})
    assert retrieved is not None
    assert len(retrieved.raw) > 0
    retrieved[
        "foo"
    ] = "bar"  # error: Unsupported target for indexed assignment
               # ("RawBSONDocument")  [index]

.. _PyCharm: https://www.jetbrains.com/help/pycharm/type-hinting-in-product.html
.. _Visual Studio Code: https://code.visualstudio.com/docs/languages/python
.. _Sublime Text: https://github.com/sublimelsp/LSP-pyright
.. _type hints: https://docs.python.org/3/library/typing.html
.. _mypy: https://mypy.readthedocs.io/en/stable/cheat_sheet_py3.html
.. _limitations in mypy: https://github.com/python/mypy/issues/3737
.. _mypy config: https://mypy.readthedocs.io/en/stable/config_file.html
.. _test_typing module: https://github.com/mongodb/mongo-python-driver/blob/master/test/test_typing.py
.. _schema validation: https://www.mongodb.com/docs/manual/core/schema-validation/#when-to-use-schema-validation