[Docs] Add entity documentation.

docs/entities.rst

@@ -0,0 +1,76 @@
+========
+Entities
+========
+
+.. _overview:
+
+Overview
+========
+
+Clastic uses doctrine to handle all data. It also give you an `Node` approach.
+Nodes are entities that have basic information.
+
+ - title (string)
+ - user (User)
+ - create (DateTime)
+ - changed (DateTime)
+ - publication (NodePublication)
+  - available (boolean)
+  - publishedFrom (DateTime)
+  - publishedTill (DateTime)
+
+.. _create_node:
+
+Create
+======
+
+You can use whatever approach you want to generate the base entity. The simplest way is to use
+the doctrine generator.
+
+.. code-block:: bash
+
+    php app/console doctrine:generate:entity
+
+Fill in all the field you need.
+
+.. note::
+
+    You don't need to define fields like title, author, ... when you choose to make them Nodes.
+
+Once you created your entity you need to alter the generated code.
+
+Object
+~~~~~~
+
+Change the `NodeReferenceInterface` to your freshly generator entity. You can also use the
+`NodeReferenceTrait` which helps you implement the interface.
+
+ex:
+
+.. code-block:: php
+
+    <?php
+    namespace Clastic\BlogBundle\Entity;
+
+    use Clastic\NodeBundle\Entity\Node;
+    use Clastic\NodeBundle\Node\NodeReferenceInterface;
+
+    class Blog implements NodeReferenceInterface
+    {
+        use NodeReferenceTrait;
+
+        // ...
+    }
+
+Definition
+~~~~~~~~~~
+
+Add the following code to your xml definition.
+
+.. code-block:: xml
+
+    <many-to-one field="node" target-entity="Clastic\NodeBundle\Entity\Node">
+      <cascade><cascade-all/></cascade>
+      <join-column name="node_id" referenced-column-name="id" />
+    </many-to-one>
+

docs/index.rst

@@ -15,5 +15,6 @@ User guide
     :maxdepth: 2
 
     overview
+    entities
     modules
 

docs/modules.rst

@@ -14,17 +14,12 @@ Clastic uses modules to expose data to the backend.
 
 To generate a module you must first create an entity.
 
-.. code-block:: bash
-
-    php app/console doctrine:generate:entity
-
-Fill in all the field you need.
+See :doc:`entities` for more information on the entities.
 
 .. note::
 
-    You don't need to define fields like title, author, ... when you choose to make them Nodes.
+    The generator only supports Node modules at the moment.
 
-Once you created your entity you can generate your module.
 
 .. code-block:: bash