python-dependency-injector/docs/_providers.rst

Providers
=========


Providers delegation
--------------------

Overriding of providers
-----------------------

Any provider can be overridden by another provider.

Example:

.. code-block:: python

    """Providers overriding example."""

    import sqlite3

    from objects.providers import Factory
    from objects.providers import Singleton

    from objects.injections import KwArg
    from objects.injections import Attribute


    class ObjectA(object):

        """ObjectA has dependency on database."""

        def __init__(self, database):
            """Initializer.

            Database dependency need to be injected via init arg."""
            self.database = database

        def get_one(self):
            """Select one from database and return it."""
            return self.database.execute('SELECT 1')


    class ObjectAMock(ObjectA):

        """Mock of ObjectA.

        Has no dependency on database.
        """

        def __init__(self):
            """Initializer."""

        def get_one(self):
            """Select one from database and return it.

            Mock makes no database queries and always returns two instead of one.
            """
            return 2


    # Database and `ObjectA` providers.
    database = Singleton(sqlite3.Connection,
                         KwArg('database', ':memory:'),
                         KwArg('timeout', 30),
                         KwArg('detect_types', True),
                         KwArg('isolation_level', 'EXCLUSIVE'),
                         Attribute('row_factory', sqlite3.Row))

    object_a_factory = Factory(ObjectA,
                               KwArg('database', database))


    # Overriding `ObjectA` provider with `ObjectAMock` provider.
    object_a_factory.override(Factory(ObjectAMock))

    # Creating several `ObjectA` instances.
    object_a_1 = object_a_factory()
    object_a_2 = object_a_factory()

    # Making some asserts.
    assert object_a_1 is not object_a_2
    assert object_a_1.get_one() == object_a_2.get_one() == 2