98 lines
3.4 KiB
Plaintext
98 lines
3.4 KiB
Plaintext
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.. _storage_strategies:
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Storage Strategies
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==================
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Doctrine MongoDB ODM implements several different strategies for persisting changes
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to mapped fields. These strategies apply to the following mapping types:
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- :ref:`int`
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- :ref:`float`
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- :ref:`embed_many`
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- :ref:`reference_many`
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For collections, Doctrine tracks changes via the PersistentCollection class. The
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strategies described on this page are implemented by the CollectionPersister
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class. The ``increment`` strategy cannot be used for collections.
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increment
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---------
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The ``increment`` strategy does not apply to collections but can be used for
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``int`` and ``float`` fields. When using the ``increment`` strategy, the field
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value will be updated using the `$inc`_ operator.
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addToSet
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--------
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The ``addToSet`` strategy uses MongoDB's `$addToSet`_ operator to insert
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elements into the array. This strategy is useful for ensuring that duplicate
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values will not be inserted into the collection. Like the `pushAll`_ strategy,
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elements are inserted in a separate query after removing deleted elements.
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set
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---
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The ``set`` strategy uses MongoDB's `$set`_ operator to update the entire
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collection with a single update query.
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.. note::
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Doctrine's Collection interface is modeled after PHP's associative arrays,
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so they cannot always be represented as a BSON array. If the collection's
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keys are not sequential integers starting with zero, the ``set`` strategy
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will store the collection as a BSON object instead of an array. Use the
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`setArray`_ strategy if you want to ensure that the collection is always
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stored as a BSON array.
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setArray
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--------
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The ``setArray`` strategy uses MongoDB's `$set`_ operator, just like the ``set``
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strategy, but will first numerically reindex the collection to ensure that it is
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stored as a BSON array.
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pushAll
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-------
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The ``pushAll`` strategy uses MongoDB's `$pushAll`_ operator to insert
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elements into the array. MongoDB does not allow elements to be added and removed
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from an array in a single operation, so this strategy relies on multiple update
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queries to remove and insert elements (in that order).
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.. _atomic_set:
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atomicSet
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---------
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The ``atomicSet`` strategy uses MongoDB's `$set`_ operator to update the entire
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collection with a single update query. Unlike with ``set`` strategy there will
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be only one query for updating both parent document and collection itself. This
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strategy can be especially useful when dealing with high concurrency and
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:ref:`versioned documents <annotations_reference_version>`.
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.. note::
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The ``atomicSet`` and ``atomicSetArray`` strategies may only be used for
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collections mapped directly in a top-level document.
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.. _atomic_set_array:
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atomicSetArray
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--------------
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The ``atomicSetArray`` strategy works exactly like ``atomicSet`` strategy, but
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will first numerically reindex the collection to ensure that it is stored as a
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BSON array.
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.. note::
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The ``atomicSet`` and ``atomicSetArray`` strategies may only be used for
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collections mapped directly in a top-level document.
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.. _`$addToSet`: https://docs.mongodb.com/manual/reference/operator/update/addToSet/
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.. _`$inc`: https://docs.mongodb.com/manual/reference/operator/update/inc/
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.. _`$pushAll`: https://docs.mongodb.com/manual/reference/operator/update/pushAll/
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.. _`$set`: https://docs.mongodb.com/manual/reference/operator/update/set/
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.. _`$unset`: https://docs.mongodb.com/manual/reference/operator/update/unset/
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