80 lines
2.3 KiB
ReStructuredText
80 lines
2.3 KiB
ReStructuredText
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Ordering To-Many Assocations
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----------------------------
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There use-cases you will want to sort collections when they are
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retrieved from the database. In userland you do this as long as you
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haven't initially saved an entity with its associations into the
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database. To retrieve a sorted collection from the database you can
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use the ``@OrderBy`` annotation with an collection that specifies
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an DQL snippet that is appended to all queries with this
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collection.
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Additional to any ``@OneToMany`` or ``@ManyToMany`` annotation you
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can specify the ``@OrderBy`` in the following way:
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.. code-block:: php
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<?php
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/** @Entity **/
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class User
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{
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// ...
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/**
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* @ManyToMany(targetEntity="Group")
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* @OrderBy({"name" = "ASC"})
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**/
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private $groups;
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}
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The DQL Snippet in OrderBy is only allowed to consist of
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unqualified, unquoted field names and of an optional ASC/DESC
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positional statement. Multiple Fields are separated by a comma (,).
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The referenced field names have to exist on the ``targetEntity``
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class of the ``@ManyToMany`` or ``@OneToMany`` annotation.
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The semantics of this feature can be described as follows.
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- ``@OrderBy`` acts as an implicit ORDER BY clause for the given
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fields, that is appended to all the explicitly given ORDER BY
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items.
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- All collections of the ordered type are always retrieved in an
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ordered fashion.
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- To keep the database impact low, these implicit ORDER BY items
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are only added to an DQL Query if the collection is fetch joined in
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the DQL query.
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Given our previously defined example, the following would not add
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ORDER BY, since g is not fetch joined:
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.. code-block:: sql
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SELECT u FROM User u JOIN u.groups g WHERE SIZE(g) > 10
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However the following:
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.. code-block:: sql
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SELECT u, g FROM User u JOIN u.groups g WHERE u.id = 10
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...would internally be rewritten to:
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.. code-block:: sql
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SELECT u, g FROM User u JOIN u.groups g WHERE u.id = 10 ORDER BY g.name ASC
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You can't reverse the order with an explicit DQL ORDER BY:
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.. code-block:: sql
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SELECT u, g FROM User u JOIN u.groups g WHERE u.id = 10 ORDER BY g.name DESC
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...is internally rewritten to:
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.. code-block:: sql
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SELECT u, g FROM User u JOIN u.groups g WHERE u.id = 10 ORDER BY g.name DESC, g.name ASC
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