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74 lines
2.4 KiB
ReStructuredText
74 lines
2.4 KiB
ReStructuredText
Singleton providers
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-------------------
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``di.Singleton`` provider creates new instance of specified class on first call
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and returns same instance on every next call.
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Example:
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.. image:: /images/providers/singleton.png
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:width: 80%
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:align: center
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.. literalinclude:: ../../examples/providers/singleton.py
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:language: python
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Singleton providers and injections
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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``di.Singleton`` providers use ``di.Factory`` providers for first creation of
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specified class instance, so, all of the rules about injections are the same,
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as for ``di.Factory`` providers.
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.. image:: /images/providers/singleton_internals.png
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:width: 80%
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:align: center
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.. note::
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Due that ``di.Singleton`` provider creates specified class instance only on
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the first call, all injections are done once, during the first call, also.
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Every next call, while instance has been already created and memorized, no
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injections are done, ``di.Singleton`` provider just returns memorized
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earlier instance.
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This may cause some problems, for example, in case of trying to bind
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``di.Factory`` provider with ``di.Singleton`` provider (provided by
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dependent ``di.Factory`` instance will be injected only once, during the
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first call). Be aware that such behaviour was made with opened eyes and is
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not a bug.
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By the way, in such case, ``di.Delegate`` provider can be useful. It makes
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possible to inject providers *as is*. Please check out full example in
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*Providers delegation* section.
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Singleton providers resetting
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Created and memorized by ``di.Singleton`` instance can be reset. Reset of
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``di.Singleton``'s memorized instance is done by clearing reference to it.
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Further lifecycle of memorized instance is out of ``di.Singleton`` provider's
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control.
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Example:
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.. literalinclude:: ../../examples/providers/singleton_reseting.py
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:language: python
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Singleton providers delegation
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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``di.Singleton`` provider could be delegated to any other provider via any
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kind of injection. Delegation of ``di.Singleton`` providers is the same as
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``di.Factory`` providers delegation, please follow
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*Factory providers delegation* section for example.
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``di.Singleton`` delegate could be created obviously using
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``di.Delegate(di.Singleton())`` or by calling ``di.Singleton.delegate()``
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method.
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Example:
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.. literalinclude:: ../../examples/providers/singleton_delegation.py
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:language: python
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