mirror of
https://github.com/ets-labs/python-dependency-injector.git
synced 2024-11-23 18:13:56 +03:00
365 lines
10 KiB
ReStructuredText
365 lines
10 KiB
ReStructuredText
Providers
|
|
=========
|
|
|
|
Providers are strategies of accessing objects.
|
|
|
|
All providers are callable. They describe how particular objects will be
|
|
provided.
|
|
|
|
|
|
Instance providers & Injections
|
|
-------------------------------
|
|
|
|
Providers
|
|
~~~~~~~~~
|
|
|
|
*Instance* providers are providers that deal with object's creation and
|
|
initialization.
|
|
|
|
There are few *Instance* providers:
|
|
|
|
- ``NewInstance`` provider creates new instance of specified class on every
|
|
call.
|
|
- ``Singleton`` provider creates new instance of specified class on first
|
|
call and returns same instance on every next call.
|
|
|
|
Example:
|
|
|
|
.. code-block:: python
|
|
|
|
"""`NewInstance` and `Singleton` providers example."""
|
|
|
|
from objects.providers import NewInstance
|
|
from objects.providers import Singleton
|
|
|
|
|
|
# NewInstance provider creates new instance of specified class on every call.
|
|
new_object = NewInstance(object)
|
|
|
|
object_1 = new_object()
|
|
object_2 = new_object()
|
|
|
|
assert object_1 is not object_2
|
|
assert isinstance(object_1, object) and isinstance(object_2, object)
|
|
|
|
# Singleton provider creates new instance of specified class on first call
|
|
# and returns same instance on every next call.
|
|
single_object = Singleton(object)
|
|
|
|
single_object_1 = single_object()
|
|
single_object_2 = single_object()
|
|
|
|
assert single_object_1 is single_object_2
|
|
assert isinstance(object_1, object) and isinstance(object_2, object)
|
|
|
|
|
|
Injections
|
|
~~~~~~~~~~
|
|
|
|
Objects can take dependencies in various forms. Some objects take init
|
|
arguments, other are using attributes or methods to be initialized. It affects
|
|
how such objects need to be created and initialized, and that is the place
|
|
where *Injections* need to be used.
|
|
|
|
In terms of computer science, *Injection of dependency* is a way how
|
|
dependency can be coupled with dependent object.
|
|
|
|
In terms of *Objects*, *Injection* is an instruction how to provide
|
|
dependency for the particular provider.
|
|
|
|
Every Python object could be an injection's value. Special case is an *Objects*
|
|
provider as an injection's value. In such case, injection value is a result of
|
|
injectable provider call (every time injection is done).
|
|
|
|
There are several types of injections. Below is a description of how they are
|
|
used by instance providers:
|
|
|
|
- ``KwArg`` - is injected in object's ``__init__()`` method in time of
|
|
object's initialization via keyword argument.
|
|
- ``Attribute`` - is injected into object's attribute (not class attribute)
|
|
after object's initialization.
|
|
- ``Method`` - is injected into object method's call after objects
|
|
initialization.
|
|
|
|
Example:
|
|
|
|
.. code-block:: python
|
|
|
|
"""`NewInstance` and `Singleton` providers with injections example."""
|
|
|
|
import sqlite3
|
|
|
|
from objects.providers import Singleton
|
|
from objects.providers import NewInstance
|
|
|
|
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').fetchone()[0]
|
|
|
|
|
|
# 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 = NewInstance(ObjectA,
|
|
KwArg('database', database))
|
|
|
|
# Creating several `ObjectA` instances.
|
|
object_a_1 = object_a()
|
|
object_a_2 = object_a()
|
|
|
|
# Making some asserts.
|
|
assert object_a_1 is not object_a_2
|
|
assert object_a_1.database is object_a_2.database is database()
|
|
assert object_a_1.get_one() == object_a_2.get_one() == 1
|
|
|
|
Static providers
|
|
----------------
|
|
|
|
Static providers are family of providers that return their values "as is".
|
|
There are four of static providers: ``Class``, ``Object``, ``Function`` and
|
|
``Value``. All of them has the same behaviour, but usage of anyone is
|
|
predicted by readability and providable object's type.
|
|
|
|
Example:
|
|
|
|
.. code-block:: python
|
|
|
|
"""Static providers example."""
|
|
|
|
from objects.providers import Class
|
|
from objects.providers import Object
|
|
from objects.providers import Function
|
|
from objects.providers import Value
|
|
|
|
|
|
cls_provider = Class(object)
|
|
assert cls_provider() is object
|
|
|
|
object_provider = Object(object())
|
|
assert isinstance(object_provider(), object)
|
|
|
|
function_provider = Function(len)
|
|
assert function_provider() is len
|
|
|
|
value_provider = Value(123)
|
|
assert value_provider() == 123
|
|
|
|
Callable providers
|
|
------------------
|
|
|
|
``Callable`` provider is a provider that decorates particular callable with
|
|
some injections. Every call of this provider returns result of call of initial
|
|
callable.
|
|
|
|
Example:
|
|
|
|
.. code-block:: python
|
|
|
|
"""`Callable` providers examples."""
|
|
|
|
from objects.providers import Callable
|
|
from objects.providers import Singleton
|
|
|
|
from objects.injections import KwArg
|
|
|
|
import sqlite3
|
|
|
|
|
|
def some_function(arg, database):
|
|
"""Example function that has input arg and dependency on database."""
|
|
return database.execute('SELECT @1', [arg]).fetchone()[0]
|
|
|
|
|
|
# Database and `ObjectA` providers.
|
|
database = Singleton(sqlite3.Connection,
|
|
KwArg('database', ':memory:'))
|
|
|
|
some_function = Callable(some_function,
|
|
KwArg('database', database))
|
|
|
|
# Some asserts.
|
|
assert some_function(1) == 1
|
|
assert some_function(2) == 2
|
|
assert some_function(2231) == 2231
|
|
|
|
|
|
External dependency providers
|
|
-----------------------------
|
|
|
|
``ExternalDependency`` provider can be useful for development of
|
|
self-sufficient libraries / modules / applications, that has required external
|
|
dependencies.
|
|
|
|
For example, you have created self-sufficient library / module / application,
|
|
that has dependency on *database connection*.
|
|
|
|
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 yours component in their applications,
|
|
because of they would be able to find right place / right way for doing this
|
|
in their application's architectures.
|
|
|
|
On the other side,
|
|
you can be sure, that your external dependency will be satisfied by appropriate
|
|
instance.
|
|
|
|
Example:
|
|
|
|
.. code-block:: python
|
|
|
|
"""External dependency providers example."""
|
|
|
|
import sqlite3
|
|
|
|
from objects.providers import Singleton
|
|
from objects.providers import NewInstance
|
|
from objects.providers import ExternalDependency
|
|
|
|
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').fetchone()[0]
|
|
|
|
|
|
# Database and `ObjectA` providers.
|
|
database = ExternalDependency(instance_of=sqlite3.Connection)
|
|
|
|
object_a = NewInstance(ObjectA,
|
|
KwArg('database', database))
|
|
|
|
# Satisfaction of external dependency.
|
|
database.override(Singleton(sqlite3.Connection,
|
|
KwArg('database', ':memory:'),
|
|
KwArg('timeout', 30),
|
|
KwArg('detect_types', True),
|
|
KwArg('isolation_level', 'EXCLUSIVE'),
|
|
Attribute('row_factory', sqlite3.Row)))
|
|
|
|
# Creating several `ObjectA` instances.
|
|
object_a_1 = object_a()
|
|
object_a_2 = object_a()
|
|
|
|
# Making some asserts.
|
|
assert object_a_1 is not object_a_2
|
|
assert object_a_1.database is object_a_2.database is database()
|
|
|
|
|
|
Config 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 Singleton
|
|
from objects.providers import NewInstance
|
|
|
|
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 = NewInstance(ObjectA,
|
|
KwArg('database', database))
|
|
|
|
|
|
# Overriding `ObjectA` provider with `ObjectAMock` provider.
|
|
object_a.override(NewInstance(ObjectAMock))
|
|
|
|
# Creating several `ObjectA` instances.
|
|
object_a_1 = object_a()
|
|
object_a_2 = object_a()
|
|
|
|
# Making some asserts.
|
|
assert object_a_1 is not object_a_2
|
|
assert object_a_1.get_one() == object_a_2.get_one() == 2
|