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149 lines
4.9 KiB
ReStructuredText
149 lines
4.9 KiB
ReStructuredText
Factory providers
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-----------------
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.. currentmodule:: dependency_injector.providers
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:py:class:`Factory` provider creates new instance of specified class on every
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call.
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Nothing could be better than brief example:
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.. image:: /images/providers/factory.png
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:width: 80%
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:align: center
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.. literalinclude:: ../../examples/providers/factory.py
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:language: python
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:linenos:
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Factory providers and __init__ injections
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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:py:class:`Factory` takes a various number of positional and keyword arguments
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that are used as ``__init__()`` injections. Every time, when
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:py:class:`Factory` creates new one instance, positional and keyword
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argument injections would be passed as an instance's arguments.
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Injections are done according to the next rules:
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+ All providers (instances of :py:class:`Provider`) are called every time
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when injection needs to be done.
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+ Providers could be injected "as is" (delegated), if it is defined obviously.
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Check out :ref:`factory_providers_delegation`.
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+ All other injectable values are provided *"as is"*.
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+ Positional context arguments will be appended after :py:class:`Factory`
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positional injections.
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+ Keyword context arguments have priority on :py:class:`Factory` keyword
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injections and will be merged over them.
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For example, if injectable value of injection is a :py:class:`Factory`, it
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will provide new one instance (as a result of its call) every time, when
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injection needs to be done.
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Example below is a little bit more complicated. It shows how to create
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:py:class:`Factory` of particular class with ``__init__()`` injections which
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injectable values are also provided by another factories:
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.. image:: /images/providers/factory_init_injections.png
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.. literalinclude:: ../../examples/providers/factory_init_injections.py
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:language: python
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:linenos:
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.. _factory_providers_delegation:
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Factory providers delegation
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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:py:class:`Factory` provider could be delegated to any other provider via any
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kind of injection.
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As it was mentioned earlier, if :py:class:`Factory` is
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injectable value, it will be called every time when injection needs to be
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done. But sometimes there is a need to inject :py:class:`Factory` provider
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itself (not a result of its call) as a dependency. Such injections are called
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- *delegated provider injections*.
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Saying in other words, delegation of factories - is a way to inject factories
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themselves, instead of results of their calls.
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:py:class:`Factory` delegation is performed by wrapping delegated
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:py:class:`Factory` into special provider type - :py:class:`Delegate`, that
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just returns wrapped :py:class:`Factory`.
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Actually, there are three ways for creating factory delegates:
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+ ``DelegatedFactory(...)`` - use special type of factory -
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:py:class:`DelegatedFactory`. Such factories are always injected as
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delegates ("as is").
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+ ``Delegate(Factory(...))`` - obviously wrapping factory into
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:py:class:`Delegate` provider.
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+ ``Factory(...).delegate()`` - calling factory :py:meth:`Factory.delegate`
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method, that returns delegate wrapper for current factory.
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Example:
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.. image:: /images/providers/factory_delegation.png
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:width: 85%
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:align: center
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.. literalinclude:: ../../examples/providers/factory_delegation.py
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:language: python
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:linenos:
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.. _factory_providers_specialization:
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Factory providers specialization
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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:py:class:`Factory` provider could be specialized for any kind of needs via
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creating its subclasses.
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One of such specialization features is a limitation to :py:class:`Factory`
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provided type:
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.. literalinclude:: ../../examples/providers/factory_provided_type.py
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:language: python
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:linenos:
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Abstract factory providers
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~~~~~~~~~~~~~~~~~~~~~~~~~~
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:py:class:`AbstractFactory` is a :py:class:`Factory` provider that must be
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explicitly overridden before calling.
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.. note::
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Overriding of :py:class:`AbstractFactory` is possible only by another
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:py:class:`Factory` provider.
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:py:class:`AbstractFactory` provider is useful when it is needed to specify
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explicitly that it only provides abstraction, but not an implementation.
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Client code must override such factories with factories that provide particular
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implementations. Otherwise, :py:class:`AbstractFactory` will raise an error
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on attempt of calling it. At the same time, :py:class:`AbstractFactory` is
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regular provider that could be injected into other providers (or used for
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any other kind of bindings) without being overridden. After
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:py:class:`AbstractFactory` provider has been overridden, its behaviour is
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identical to regular :py:class:`Factory` provider.
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Example:
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.. image:: /images/providers/abstract_factory.png
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:width: 100%
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:align: center
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Listing of ``cache.py``:
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.. literalinclude:: ../../examples/providers/abstract_factory/cache.py
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:language: python
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:linenos:
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Listing of ``example.py``:
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.. literalinclude:: ../../examples/providers/abstract_factory/example.py
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:language: python
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:linenos:
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.. disqus::
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