359 lines
14 KiB
ReStructuredText
359 lines
14 KiB
ReStructuredText
Native SQL
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==========
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A ``NativeQuery`` lets you execute native SQL, mapping the results
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according to your specifications. Such a specification that
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describes how an SQL result set is mapped to a Doctrine result is
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represented by a ``ResultSetMapping``. It describes how each column
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of the database result should be mapped by Doctrine in terms of the
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object graph. This allows you to map arbitrary SQL code to objects,
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such as highly vendor-optimized SQL or stored-procedures.
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The NativeQuery class
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---------------------
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To create a ``NativeQuery`` you use the method
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``EntityManager#createNativeQuery($sql, $resultSetMapping)``. As
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you can see in the signature of this method, it expects 2
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ingredients: The SQL you want to execute and the
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``ResultSetMapping`` that describes how the results will be
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mapped.
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Once you obtained an instance of a ``NativeQuery``, you can bind
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parameters to it and finally execute it.
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The ResultSetMapping
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--------------------
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Understanding the ``ResultSetMapping`` is the key to using a
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``NativeQuery``. A Doctrine result can contain the following
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components:
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- Entity results. These represent root result elements.
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- Joined entity results. These represent joined entities in
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associations of root entity results.
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- Field results. These represent a column in the result set that
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maps to a field of an entity. A field result always belongs to an
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entity result or joined entity result.
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- Scalar results. These represent scalar values in the result set
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that will appear in each result row. Adding scalar results to a
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ResultSetMapping can also cause the overall result to become
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**mixed** (see DQL - Doctrine Query Language) if the same
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ResultSetMapping also contains entity results.
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- Meta results. These represent columns that contain
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meta-information, such as foreign keys and discriminator columns.
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When querying for objects (``getResult()``), all meta columns of
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root entities or joined entities must be present in the SQL query
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and mapped accordingly using ``ResultSetMapping#addMetaResult``.
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.. note::
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It might not surprise you that Doctrine uses
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``ResultSetMapping``s internally when you create DQL queries. As
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the query gets parsed and transformed to SQL, Doctrine fills a
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``ResultSetMapping`` that describes how the results should be
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processed by the hydration routines.
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We will now look at each of the result types that can appear in a
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ResultSetMapping in detail.
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Entity results
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~~~~~~~~~~~~~~
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An entity result describes an entity type that appears as a root
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element in the transformed result. You add an entity result through
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``ResultSetMapping#addEntityResult()``. Let's take a look at the
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method signature in detail:
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::
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<?php
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/**
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* Adds an entity result to this ResultSetMapping.
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*
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* @param string $class The class name of the entity.
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* @param string $alias The alias for the class. The alias must be unique among all entity
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* results or joined entity results within this ResultSetMapping.
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*/
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public function addEntityResult($class, $alias)
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The first parameter is the fully qualified name of the entity
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class. The second parameter is some arbitrary alias for this entity
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result that must be unique within a ``ResultSetMapping``. You use
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this alias to attach field results to the entity result. It is very
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similar to an identification variable that you use in DQL to alias
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classes or relationships.
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An entity result alone is not enough to form a valid
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``ResultSetMapping``. An entity result or joined entity result
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always needs a set of field results, which we will look at soon.
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Joined entity results
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~~~~~~~~~~~~~~~~~~~~~
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A joined entity result describes an entity type that appears as a
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joined relationship element in the transformed result, attached to
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a (root) entity result. You add a joined entity result through
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``ResultSetMapping#addJoinedEntityResult()``. Let's take a look at
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the method signature in detail:
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::
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<?php
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/**
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* Adds a joined entity result.
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*
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* @param string $class The class name of the joined entity.
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* @param string $alias The unique alias to use for the joined entity.
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* @param string $parentAlias The alias of the entity result that is the parent of this joined result.
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* @param object $relation The association field that connects the parent entity result with the joined entity result.
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*/
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public function addJoinedEntityResult($class, $alias, $parentAlias, $relation)
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The first parameter is the class name of the joined entity. The
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second parameter is an arbitrary alias for the joined entity that
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must be unique within the ``ResultSetMapping``. You use this alias
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to attach field results to the entity result. The third parameter
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is the alias of the entity result that is the parent type of the
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joined relationship. The fourth and last parameter is the name of
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the field on the parent entity result that should contain the
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joined entity result.
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Field results
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~~~~~~~~~~~~~
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A field result describes the mapping of a single column in an SQL
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result set to a field in an entity. As such, field results are
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inherently bound to entity results. You add a field result through
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``ResultSetMapping#addFieldResult()``. Again, let's examine the
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method signature in detail:
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::
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<?php
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/**
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* Adds a field result that is part of an entity result or joined entity result.
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*
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* @param string $alias The alias of the entity result or joined entity result.
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* @param string $columnName The name of the column in the SQL result set.
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* @param string $fieldName The name of the field on the (joined) entity.
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*/
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public function addFieldResult($alias, $columnName, $fieldName)
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The first parameter is the alias of the entity result to which the
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field result will belong. The second parameter is the name of the
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column in the SQL result set. Note that this name is case
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sensitive, i.e. if you use a native query against Oracle it must be
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all uppercase. The third parameter is the name of the field on the
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entity result identified by ``$alias`` into which the value of the
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column should be set.
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Scalar results
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~~~~~~~~~~~~~~
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A scalar result describes the mapping of a single column in an SQL
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result set to a scalar value in the Doctrine result. Scalar results
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are typically used for aggregate values but any column in the SQL
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result set can be mapped as a scalar value. To add a scalar result
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use ``ResultSetMapping#addScalarResult()``. The method signature in
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detail:
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::
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<?php
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/**
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* Adds a scalar result mapping.
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*
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* @param string $columnName The name of the column in the SQL result set.
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* @param string $alias The result alias with which the scalar result should be placed in the result structure.
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*/
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public function addScalarResult($columnName, $alias)
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The first parameter is the name of the column in the SQL result set
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and the second parameter is the result alias under which the value
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of the column will be placed in the transformed Doctrine result.
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Meta results
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~~~~~~~~~~~~
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A meta result describes a single column in an SQL result set that
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is either a foreign key or a discriminator column. These columns
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are essential for Doctrine to properly construct objects out of SQL
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result sets. To add a column as a meta result use
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``ResultSetMapping#addMetaResult()``. The method signature in
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detail:
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::
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<?php
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/**
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* Adds a meta column (foreign key or discriminator column) to the result set.
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*
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* @param string $alias
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* @param string $columnAlias
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* @param string $columnName
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*/
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public function addMetaResult($alias, $columnAlias, $columnName)
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The first parameter is the alias of the entity result to which the
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meta column belongs. A meta result column (foreign key or
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discriminator column) always belongs to to an entity result. The
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second parameter is the column alias/name of the column in the SQL
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result set and the third parameter is the column name used in the
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mapping.
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Discriminator Column
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~~~~~~~~~~~~~~~~~~~~
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When joining an inheritance tree you have to give Doctrine a hint
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which meta-column is the discriminator column of this tree.
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::
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<?php
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/**
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* Sets a discriminator column for an entity result or joined entity result.
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* The discriminator column will be used to determine the concrete class name to
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* instantiate.
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*
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* @param string $alias The alias of the entity result or joined entity result the discriminator
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* column should be used for.
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* @param string $discrColumn The name of the discriminator column in the SQL result set.
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* @todo Rename: addDiscriminatorColumn
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*/
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public function setDiscriminatorColumn($alias, $discrColumn)
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Examples
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~~~~~~~~
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Understanding a ResultSetMapping is probably easiest through
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looking at some examples.
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First a basic example that describes the mapping of a single
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entity.
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<?php
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// Equivalent DQL query: "select u from User u where u.name=?1"
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// User owns no associations.
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$rsm = new ResultSetMapping;
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$rsm->addEntityResult('User', 'u');
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$rsm->addFieldResult('u', 'id', 'id');
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$rsm->addFieldResult('u', 'name', 'name');
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$query = $this->_em->createNativeQuery('SELECT id, name FROM users WHERE name = ?', $rsm);
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$query->setParameter(1, 'romanb');
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$users = $query->getResult();
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The result would look like this:
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::
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array(
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[0] => User (Object)
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)
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Note that this would be a partial object if the entity has more
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fields than just id and name. In the example above the column and
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field names are identical but that is not necessary, of course.
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Also note that the query string passed to createNativeQuery is
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**real native SQL**. Doctrine does not touch this SQL in any way.
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In the previous basic example, a User had no relations and the
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table the class is mapped to owns no foreign keys. The next example
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assumes User has a unidirectional or bidirectional one-to-one
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association to a CmsAddress, where the User is the owning side and
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thus owns the foreign key.
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::
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<?php
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// Equivalent DQL query: "select u from User u where u.name=?1"
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// User owns an association to an Address but the Address is not loaded in the query.
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$rsm = new ResultSetMapping;
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$rsm->addEntityResult('User', 'u');
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$rsm->addFieldResult('u', 'id', 'id');
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$rsm->addFieldResult('u', 'name', 'name');
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$rsm->addMetaResult('u', 'address_id', 'address_id');
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$query = $this->_em->createNativeQuery('SELECT id, name, address_id FROM users WHERE name = ?', $rsm);
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$query->setParameter(1, 'romanb');
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$users = $query->getResult();
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Foreign keys are used by Doctrine for lazy-loading purposes when
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querying for objects. In the previous example, each user object in
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the result will have a proxy (a "ghost") in place of the address
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that contains the address\_id. When the ghost proxy is accessed, it
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loads itself based on this key.
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Consequently, associations that are *fetch-joined* do not require
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the foreign keys to be present in the SQL result set, only
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associations that are lazy.
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::
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<?php
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// Equivalent DQL query: "select u from User u join u.address a WHERE u.name = ?1"
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// User owns association to an Address and the Address is loaded in the query.
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$rsm = new ResultSetMapping;
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$rsm->addEntityResult('User', 'u');
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$rsm->addFieldResult('u', 'id', 'id');
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$rsm->addFieldResult('u', 'name', 'name');
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$rsm->addJoinedEntityResult('Address' , 'a', 'u', 'address');
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$rsm->addFieldResult('a', 'address_id', 'id');
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$rsm->addFieldResult('a', 'street', 'street');
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$rsm->addFieldResult('a', 'city', 'city');
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$sql = 'SELECT u.id, u.name, a.id AS address_id, a.street, a.city FROM users u ' .
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'INNER JOIN address a ON u.address_id = a.id WHERE u.name = ?';
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$query = $this->_em->createNativeQuery($sql, $rsm);
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$query->setParameter(1, 'romanb');
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$users = $query->getResult();
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In this case the nested entity ``Address`` is registered with the
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``ResultSetMapping#addJoinedEntityResult`` method, which notifies
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Doctrine that this entity is not hydrated at the root level, but as
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a joined entity somewhere inside the object graph. In this case we
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specify the alias 'u' as third parameter and ``address`` as fourth
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parameter, which means the ``Address`` is hydrated into the
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``User::$address`` property.
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If a fetched entity is part of a mapped hierarchy that requires a
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discriminator column, this column must be present in the result set
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as a meta column so that Doctrine can create the appropriate
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concrete type. This is shown in the following example where we
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assume that there are one or more subclasses that extend User and
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either Class Table Inheritance or Single Table Inheritance is used
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to map the hierarchy (both use a discriminator column).
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::
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<?php
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// Equivalent DQL query: "select u from User u where u.name=?1"
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// User is a mapped base class for other classes. User owns no associations.
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$rsm = new ResultSetMapping;
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$rsm->addEntityResult('User', 'u');
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$rsm->addFieldResult('u', 'id', 'id');
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$rsm->addFieldResult('u', 'name', 'name');
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$rsm->addMetaResult('u', 'discr', 'discr'); // discriminator column
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$rsm->setDiscriminatorColumn('u', 'discr');
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$query = $this->_em->createNativeQuery('SELECT id, name, discr FROM users WHERE name = ?', $rsm);
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$query->setParameter(1, 'romanb');
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$users = $query->getResult();
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Note that in the case of Class Table Inheritance, an example as
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above would result in partial objects if any objects in the result
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are actually a subtype of User. When using DQL, Doctrine
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automatically includes the necessary joins for this mapping
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strategy but with native SQL it is your responsibility.
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