DDC-153 - Added cookbook entry contributed by merk (thanks!)

cookbook/en.txt

@@ -6,3 +6,4 @@
 + Integrating with CodeIgniter
 + DQL Custom Walkers
 + DQL User Defined Functions
++ SQL Table Prefixes

cookbook/en/sql-table-prefixes.txt

@@ -0,0 +1,51 @@
+This recipe is intended as an example of implementing a loadClassMetadata listener to provide a Table Prefix option for your application. The method used below is not a hack, but fully integrates into the Doctrine system, all SQL generated will include the appropriate table prefix.
+
+In most circumstances it is desirable to separate different applications into individual databases, but in certain cases, it may be beneficial to have a table prefix for your Entities to separate them from other vendor products in the same database.
+
+++ Implementing the listener
+
+The listener in this example has been set up with the DoctrineExtensions namespace. You create this file in your library/DoctrineExtensions directory, but will need to set up appropriate autoloaders.
+
+    [php]
+    <?php
+
+    namespace DoctrineExtensions;
+    use \Doctrine\ORM\Event\LoadClassMetadataEventArgs;
+
+    class TablePrefix
+    {
+        protected $_prefix = '';
+
+        public function __construct($prefix)
+        {
+            $this->_prefix = (string) $prefix;
+        }
+
+        public function loadClassMetadata(LoadClassMetadataEventArgs $eventArgs)
+        {
+            $classMetadata = $eventArgs->getClassMetadata();
+            $classMetadata->setTableName($this->_prefix . $classMetadata->getTableName());
+        }
+    }
+
+++ Telling the EntityManager about our listener
+
+A listener of this type must be set up before the EntityManager has been initialised, otherwise an Entity might be created or cached before the prefix has been set.
+
+> **Note**
+> If you set this listener up, be aware that you will need to clear your caches
+> and drop then recreate your database schema.
+
+    [php]
+    <?php
+
+    // $connectionOptions and $config set earlier
+
+    $evm = new \Doctrine\Common\EventManager;
+
+    // Table Prefix
+    $tablePrefix = new \DoctrineExtensions\TablePrefix('prefix_');
+    $evm->addEventListener(\Doctrine\ORM\Events::loadClassMetadata, $tablePrefix);
+
+    $em = \Doctrine\ORM\EntityManager::create($connectionOptions, $config, $evm);
+