Merge pull request #7 from lsmith77/caching

initial docs for cache integration

en/index.rst

@@ -28,6 +28,7 @@ Contents:
    reference/sharding_azure_tutorial
    reference/supporting-other-databases
    reference/portability
+   reference/caching
    reference/known-vendor-issues
 
 Indices and tables

en/reference/caching.rst

+Caching
+=======
+
+A ``Doctrine\DBAL\Statement`` can automatically cache result sets.
+
+For this to work an instance of ``Doctrine\Common\Cache\Cache`` must be provided.
+This can be set on the configuration object (optionally it can also be passed at query time):
+
+::
+
+    <?php
+    $cache = new \Doctrine\Common\Cache\ArrayCache();
+    $config = $conn->getConfiguration();
+    $config->setResultCacheImpl($cache);
+
+To get the result set of a query cached it is necessary to pass a
+``Doctrine\DBAL\Cache\QueryCacheProfile`` instance to the ``executeQuery`` or ``executeCacheQuery``
+instance. The difference between these two methods is that the former does not
+require this instance, while the later has this instance as a required parameter:
+
+::
+
+    <?php
+    $stmt = $conn->executeQuery($query, $params, $types, new QueryCacheProfile(0, "some key"));
+    $stmt = $conn->executeCachedQuery($query, $params, $types, new QueryCacheProfile(0, "some key"));
+
+It is also possible to pass in a the ``Doctrine\Common\Cache\Cache`` instance into the
+constructor of ``Doctrine\DBAL\Cache\QueryCacheProfile`` in which case it overrides
+the default cache instance:
+
+::
+
+    <?php
+    $cache = new \Doctrine\Common\Cache\FilesystemCache(__DIR__);
+    new QueryCacheProfile(0, "some key", $cache);
+
+In order for the data to actually be cached its necessary to ensure that the entire
+result set is read (easiest way to ensure this is to use ``fetchAll``) and the statement
+object is closed:
+
+::
+
+    <?php
+    $stmt = $conn->executeCachedQuery($query, $params, $types, new QueryCacheProfile(0, "some key"));
+    $data = $stmt->fetchAll();
+    $stmt->close() // at this point the result is cached
+
+
+.. warning::
+
+    When using the cache layer not all fetch modes are supported. See the code of the
+`ResultCacheStatement 
+<https://github.com/doctrine/dbal/blob/master/lib/Doctrine/DBAL/Cache/ResultCacheStatement.php#L156>`_ for details.
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