Edit Dependency provider docs

docs/main/changelog.rst

@@ -10,7 +10,7 @@ follows `Semantic versioning`_
 Development version
 -------------------
 - Update documentation and rework examples for: ``Singleton``, ``Callable``, ``Coroutine``,
-  ``Object``, ``List``, ``Configuration``, ``Selector`` providers.
+  ``Object``, ``List``, ``Configuration``, ``Selector``, and ``Dependency`` providers.
 - Fix mypy stub of the ``DeclarativeContainer`` to specify the ``__init__`` interface.
 
 3.34.0

docs/providers/dependency.rst

@@ -1,43 +1,21 @@
-Dependency providers
---------------------
+Dependency provider
+-------------------
 
 .. currentmodule:: dependency_injector.providers
 
-:py:class:`Dependency` provider can be useful for development of
-self-sufficient libraries / modules / applications that have required external
-dependencies.
+:py:class:`Dependency` provider is a placeholder for the dependency of the specified type.
 
-For example, you have created self-sufficient library / module / application,
-that has dependency on *database connection*.
+The first argument of the ``Dependency`` provider specifies a type of the dependency. It is
+called ``instance_of``. ``Dependency`` provider controls the type of the returned object to be an
+instance of the ``instance_of`` type.
 
-Second step you want to do is to make this software component to be easy
-reusable by wide amount of developers and to be easily integrated into many
-applications.
-
-It may be good idea, to move all external dependencies (like
-*database connection*) to the top level and make them to be injected on your
-software component's initialization. It will make third party developers feel
-themselves free about integration of your component in their applications,
-because they would be able to find right place / right way for doing this
-in their application's architectures.
-
-At the same time, you can be sure, that your external dependency will be
-satisfied with appropriate instance.
-
-Example:
-
-.. note::
-
-    Class ``UsersService`` is a part of some library. ``UsersService`` has
-    dependency on database connection, which can be satisfied with any
-    DBAPI 2.0 database connection. Being a self-sufficient library,
-    ``UsersService`` doesn't hardcode any kind of database management logic.
-    Instead of this, ``UsersService`` has external dependency, that has to
-    be satisfied by client's code, out of library's scope.
-
-.. image:: /images/providers/dependency.png
+The ``Dependency`` provider must be overridden before usage. It can be overridden by any type of
+the provider. The only rule is that overriding provider must return an instance of ``instance_of``
+dependency type.
 
 .. literalinclude:: ../../examples/providers/dependency.py
    :language: python
+   :lines: 3-
+   :emphasize-lines: 26
 
 .. disqus::

examples/providers/dependency.py

@@ -1,73 +1,50 @@
-"""`Dependency` providers example."""
+"""`Dependency` provider example."""
 
-import sqlite3
-import contextlib
+import abc
+import dataclasses
 
-import dependency_injector.providers as providers
+from dependency_injector import containers, providers, errors
 
 
-class UsersService:
-    """Example class UsersService.
+class DbAdapter(metaclass=abc.ABCMeta):
+    ...
 
-    UsersService has dependency on DBAPI 2.0 database connection.
-    """
 
-    def __init__(self, database):
-        """Initialize instance.
+class SqliteDbAdapter(DbAdapter):
+    ...
 
-        :param database: Database connection.
-        :type database: sqlite3.dbapi2.Connection
-        """
-        self.database = database
-        self.database.row_factory = sqlite3.dbapi2.Row
 
-    def init_database(self):
-        """Initialize database, if it has not been initialized yet."""
-        with contextlib.closing(self.database.cursor()) as cursor:
-            cursor.execute("""
-              CREATE TABLE IF NOT EXISTS users(
-                id INTEGER PRIMARY KEY AUTOINCREMENT,
-                name VARCHAR(32)
+class PostgresDbAdapter(DbAdapter):
+    ...
+
+
+@dataclasses.dataclass
+class UserService:
+    database: DbAdapter
+
+
+class Container(containers.DeclarativeContainer):
+
+    database = providers.Dependency(instance_of=DbAdapter)
+
+    user_service = providers.Factory(
+        UserService,
+        database=database,
     )
-            """)
-
-    def create(self, name):
-        """Create user with provided name and return his id."""
-        with contextlib.closing(self.database.cursor()) as cursor:
-            cursor.execute('INSERT INTO users(name) VALUES (?)', (name,))
-            return cursor.lastrowid
-
-    def get_by_id(self, id):
-        """Return user info by user id."""
-        with contextlib.closing(self.database.cursor()) as cursor:
-            cursor.execute('SELECT id, name FROM users WHERE id=?', (id,))
-            return cursor.fetchone()
 
 
-# Database and UsersService providers:
-database = providers.Dependency(instance_of=sqlite3.dbapi2.Connection)
-users_service_factory = providers.Factory(UsersService,
-                                          database=database)
+if __name__ == '__main__':
+    container1 = Container(database=providers.Singleton(SqliteDbAdapter))
+    container2 = Container(database=providers.Singleton(PostgresDbAdapter))
 
-# Out of library's scope.
-#
-# Setting database provider:
-database.provided_by(providers.Singleton(sqlite3.dbapi2.Connection,
-                                         database=':memory:',
-                                         timeout=30,
-                                         detect_types=True,
-                                         isolation_level='EXCLUSIVE'))
+    assert isinstance(container1.user_service().database, SqliteDbAdapter)
+    assert isinstance(container2.user_service().database, PostgresDbAdapter)
 
-# Creating UsersService instance:
-users_service = users_service_factory()
-
-# Initializing UsersService database:
-users_service.init_database()
-
-# Creating test user and retrieving full information about him:
-test_user_id = users_service.create(name='test_user')
-test_user = users_service.get_by_id(test_user_id)
-
-# Making some asserts:
-assert test_user['id'] == 1
-assert test_user['name'] == 'test_user'
+    container3 = Container(database=providers.Singleton(object))
+    try:
+        container3.user_service()
+    except errors.Error as exception:
+        print(exception)
+        # The output is:
+        # <object object at 0x107ce5c40> is not an
+        # instance of <class '__main__.DbAdapter'>