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Merge pull request #11403 from ThomasLandauer/patch-10
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[Documentation] Merging "Query Result Formats" with "Hydration Modes"
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@greg0ire
greg0ire authored Mar 28, 2024
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331 changes: 138 additions & 193 deletions docs/en/reference/dql-doctrine-query-language.rst
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Expand Up @@ -1020,42 +1020,146 @@ Alternatively you can create an empty ``Query`` instance and invoke
$q = $em->createQuery();
$q->setDQL('select u from MyProject\Model\User u');
Query Result Formats
~~~~~~~~~~~~~~~~~~~~
Query Result Formats (Hydration Modes)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The way in which the SQL result set of a DQL SELECT query is transformed
to PHP is determined by the so-called "hydration mode":

- **``getResult()``** (``HYDRATE_OBJECT``): Retrieves a collection of objects. The
result is either a plain collection of objects (pure) or an array
where the objects are nested in the result rows (mixed).
- **``getSingleResult()``**: Retrieves a single object. If the
result contains more than one object, a ``NonUniqueResultException``
is thrown. If the result contains no objects, a ``NoResultException``
is thrown. The pure/mixed distinction does not apply.
- **``getOneOrNullResult()``**: Retrieve a single object. If the
result contains more than one object, a ``NonUniqueResultException``
is thrown. If no object is found null will be returned.
- **``getArrayResult()``** (``HYDRATE_ARRAY``): Retrieves an array graph (a nested
array) for read-only purposes.

.. note::

An array graph can differ from the corresponding object
graph in certain scenarios due to the difference of the identity
semantics between arrays and objects.

- **``getScalarResult()``** (``HYDRATE_SCALAR``): Retrieves a flat/rectangular result
set of scalar values that can contain duplicate data. The
pure/mixed distinction does not apply.
- **``getSingleScalarResult()``** (``HYDRATE_SINGLE_SCALAR``: Retrieves a single scalar
value from the result returned by the dbms. If the result contains
more than a single scalar value, a ``NonUniqueResultException`` is thrown. The
pure/mixed distinction does not apply.

In parentheses are the constants of the ``Query`` class which you can use with the
general-purpose method ``Query::execute(array $params = [], $hydrationMode = Query::HYDRATE_OBJECT)``.
In fact, the methods in the list are just convenient shortcuts for the hydration mode.
to PHP is determined by the so-called "hydration mode".

``getResult()``
^^^^^^^^^^^^^^^

Retrieves a collection of objects. The result is either a plain collection of objects (pure) or an array
where the objects are nested in the result rows (mixed):

.. code-block:: php
<?php
use Doctrine\ORM\AbstractQuery;
$query = $em->createQuery('SELECT u FROM User u');
$users = $query->getResult();
// same as:
$users = $query->getResult(AbstractQuery::HYDRATE_OBJECT);
- Objects fetched in a FROM clause are returned as a Set, that means every
object is only ever included in the resulting array once. This is the case
even when using JOIN or GROUP BY in ways that return the same row for an
object multiple times. If the hydrator sees the same object multiple times,
then it makes sure it is only returned once.

- If an object is already in memory from a previous query of any kind, then
then the previous object is used, even if the database may contain more
recent data. This even happens if the previous object is still an unloaded proxy.

``getArrayResult()``
^^^^^^^^^^^^^^^^^^^^

Retrieves an array graph (a nested array) for read-only purposes.

.. note::

An array graph can differ from the corresponding object
graph in certain scenarios due to the difference of the identity
semantics between arrays and objects.

.. code-block:: php
<?php
$users = $query->getArrayResult();
// same as:
$users = $query->getResult(AbstractQuery::HYDRATE_ARRAY);
``getScalarResult()``
^^^^^^^^^^^^^^^^^^^^^

Retrieves a flat/rectangular result set of scalar values that can contain duplicate data. The
pure/mixed distinction does not apply.

.. code-block:: php
<?php
$users = $query->getScalarResult();
// same as:
$users = $query->getResult(AbstractQuery::HYDRATE_SCALAR);
Fields from classes are prefixed by the DQL alias in the result.
A query of the kind `SELECT u.name ...` returns a key `u_name` in the result rows.

``getSingleScalarResult()``
^^^^^^^^^^^^^^^^^^^^^^^^^^^

Retrieves a single scalar value from the result returned by the database. If the result contains
more than a single scalar value, a ``NonUniqueResultException`` is thrown. The pure/mixed distinction does not apply.

.. code-block:: php
<?php
$query = $em->createQuery('SELECT COUNT(u.id) FROM User u');
$numUsers = $query->getSingleScalarResult();
// same as:
$numUsers = $query->getResult(AbstractQuery::HYDRATE_SINGLE_SCALAR);
``getSingleColumnResult()``
^^^^^^^^^^^^^^^^^^^^^^^^^^^

Retrieves an array from a one-dimensional array of scalar values:

.. code-block:: php
<?php
$query = $em->createQuery('SELECT a.id FROM User u');
$ids = $query->getSingleColumnResult();
// same as:
$ids = $query->getResult(AbstractQuery::HYDRATE_SCALAR_COLUMN);
``getSingleResult()``
^^^^^^^^^^^^^^^^^^^^^

Retrieves a single object. If the result contains more than one object, a ``NonUniqueResultException``
is thrown. If the result contains no objects, a ``NoResultException`` is thrown. The pure/mixed distinction does not apply.

``getOneOrNullResult()``
^^^^^^^^^^^^^^^^^^^^^^^^

Retrieves a single object. If the result contains more than one object, a ``NonUniqueResultException``
is thrown. If no object is found, ``null`` will be returned.

Custom Hydration Modes
^^^^^^^^^^^^^^^^^^^^^^

You can easily add your own custom hydration modes by first
creating a class which extends ``AbstractHydrator``:

.. code-block:: php
<?php
namespace MyProject\Hydrators;
use Doctrine\ORM\Internal\Hydration\AbstractHydrator;
class CustomHydrator extends AbstractHydrator
{
protected function _hydrateAll()
{
return $this->_stmt->fetchAllAssociative();
}
}
Next you just need to add the class to the ORM configuration:

.. code-block:: php
<?php
$em->getConfiguration()->addCustomHydrationMode('CustomHydrator', 'MyProject\Hydrators\CustomHydrator');
Now the hydrator is ready to be used in your queries:

.. code-block:: php
<?php
$query = $em->createQuery('SELECT u FROM CmsUser u');
$results = $query->getResult('CustomHydrator');
Pure and Mixed Results
~~~~~~~~~~~~~~~~~~~~~~
Expand Down Expand Up @@ -1159,165 +1263,6 @@ will return the rows iterating the different top-level entities.
[2] => Object (User)
[3] => Object (Group)
Hydration Modes
~~~~~~~~~~~~~~~

Each of the Hydration Modes makes assumptions about how the result
is returned to user land. You should know about all the details to
make best use of the different result formats:

The constants for the different hydration modes are:


- ``Query::HYDRATE_OBJECT``
- ``Query::HYDRATE_ARRAY``
- ``Query::HYDRATE_SCALAR``
- ``Query::HYDRATE_SINGLE_SCALAR``
- ``Query::HYDRATE_SCALAR_COLUMN``

Object Hydration
^^^^^^^^^^^^^^^^

Object hydration hydrates the result set into the object graph:

.. code-block:: php
<?php
$query = $em->createQuery('SELECT u FROM CmsUser u');
$users = $query->getResult(Query::HYDRATE_OBJECT);
Sometimes the behavior in the object hydrator can be confusing, which is
why we are listing as many of the assumptions here for reference:

- Objects fetched in a FROM clause are returned as a Set, that means every
object is only ever included in the resulting array once. This is the case
even when using JOIN or GROUP BY in ways that return the same row for an
object multiple times. If the hydrator sees the same object multiple times,
then it makes sure it is only returned once.

- If an object is already in memory from a previous query of any kind, then
then the previous object is used, even if the database may contain more
recent data. Data from the database is discarded. This even happens if the
previous object is still an unloaded proxy.

This list might be incomplete.

Array Hydration
^^^^^^^^^^^^^^^

You can run the same query with array hydration and the result set
is hydrated into an array that represents the object graph:

.. code-block:: php
<?php
$query = $em->createQuery('SELECT u FROM CmsUser u');
$users = $query->getResult(Query::HYDRATE_ARRAY);
You can use the ``getArrayResult()`` shortcut as well:

.. code-block:: php
<?php
$users = $query->getArrayResult();
Scalar Hydration
^^^^^^^^^^^^^^^^

If you want to return a flat rectangular result set instead of an
object graph you can use scalar hydration:

.. code-block:: php
<?php
$query = $em->createQuery('SELECT u FROM CmsUser u');
$users = $query->getResult(Query::HYDRATE_SCALAR);
echo $users[0]['u_id'];
The following assumptions are made about selected fields using
Scalar Hydration:


1. Fields from classes are prefixed by the DQL alias in the result.
A query of the kind 'SELECT u.name ..' returns a key 'u_name' in
the result rows.

Single Scalar Hydration
^^^^^^^^^^^^^^^^^^^^^^^

If you have a query which returns just a single scalar value you can use
single scalar hydration:

.. code-block:: php
<?php
$query = $em->createQuery('SELECT COUNT(a.id) FROM CmsUser u LEFT JOIN u.articles a WHERE u.username = ?1 GROUP BY u.id');
$query->setParameter(1, 'jwage');
$numArticles = $query->getResult(Query::HYDRATE_SINGLE_SCALAR);
You can use the ``getSingleScalarResult()`` shortcut as well:

.. code-block:: php
<?php
$numArticles = $query->getSingleScalarResult();
Scalar Column Hydration
^^^^^^^^^^^^^^^^^^^^^^^

If you have a query which returns a one-dimensional array of scalar values
you can use scalar column hydration:

.. code-block:: php
<?php
$query = $em->createQuery('SELECT a.id FROM CmsUser u');
$ids = $query->getResult(Query::HYDRATE_SCALAR_COLUMN);
You can use the ``getSingleColumnResult()`` shortcut as well:

.. code-block:: php
<?php
$ids = $query->getSingleColumnResult();
Custom Hydration Modes
^^^^^^^^^^^^^^^^^^^^^^

You can easily add your own custom hydration modes by first
creating a class which extends ``AbstractHydrator``:

.. code-block:: php
<?php
namespace MyProject\Hydrators;
use Doctrine\ORM\Internal\Hydration\AbstractHydrator;
class CustomHydrator extends AbstractHydrator
{
protected function _hydrateAll()
{
return $this->_stmt->fetchAllAssociative();
}
}
Next you just need to add the class to the ORM configuration:

.. code-block:: php
<?php
$em->getConfiguration()->addCustomHydrationMode('CustomHydrator', 'MyProject\Hydrators\CustomHydrator');
Now the hydrator is ready to be used in your queries:

.. code-block:: php
<?php
$query = $em->createQuery('SELECT u FROM CmsUser u');
$results = $query->getResult('CustomHydrator');
Iterating Large Result Sets
~~~~~~~~~~~~~~~~~~~~~~~~~~~

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