First part of a tutorial on composite primary keys and identity through foreign entities.

en/index.rst

@@ -44,6 +44,7 @@ Tutorials
    tutorials/getting-started-xml-edition
    tutorials/working-with-indexed-associations
    tutorials/extra-lazy-associations
+   tutorials/composite-primary-keys
 
 
 Cookbook

en/tutorials/composite-primary-keys.rst

@@ -0,0 +1,211 @@
+Composite Primary Keys
+======================
+
+Doctrine 2 supports composite primary keys natively. Composite keys are a very powerful relational database concept
+and we took good care to make sure Doctrine 2 supports as many of the composite primary key use-cases.
+For Doctrine 2.0 composite keys of primitive data-types are supported, for Doctrine 2.1 even foreign keys as
+primary keys are supported.
+
+This tutorial shows how the semantics of composite primary keys work and how they map to the database.
+
+General Considerations
+~~~~~~~~~~~~~~~~~~~~~~
+
+Every entity with a composite key cannot use an id generator other than "ASSIGNED". That means
+the ID fields have to have their values set before you call ``EntityManager#persist($entity)``.
+
+Primitive Types only
+~~~~~~~~~~~~~~~~~~~~
+
+Even in version 2.0 you can have composite keys as long as they only consist of the primative types
+``integer`` and ``string``. Suppose you want to create a database of cars and use the model-name
+and year of production as primary keys:
+
+.. configuration-block::
+
+    .. code-block:: php
+
+        <?php
+        namespace VehicleCatalogue\Model;
+
+        /**
+         * @Entity
+         */
+        class Car
+        {
+            /** @Id @Column(type="string") */
+            private $name;
+            /** @Id @Column(type="integer") */
+            private $year
+
+            public function __construct($name, $year)
+            {
+                $this->name = $name;
+                $this->year = $year;
+            }
+
+            public function getModelName()
+            {
+                return $this->name;
+            }
+
+            public function getYearOfProduction()
+            {
+                return $this->year;
+            }
+        }
+
+    .. code-block:: xml
+
+        <?xml version="1.0" encoding="UTF-8"?>
+        <doctrine-mapping xmlns="http://doctrine-project.org/schemas/orm/doctrine-mapping"
+              xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+              xsi:schemaLocation="http://doctrine-project.org/schemas/orm/doctrine-mapping
+                                  http://www.doctrine-project.org/schemas/orm/doctrine-mapping.xsd">
+
+            <entity name="VehicleCatalogue\Model\Car">
+                <id field="name" type="string" />
+                <id field="year" type="integer" />
+            </entity>
+        </doctrine-mapping>
+
+    .. code-block:: yaml
+
+        VehicleCatalogue\Model\Car:
+          type: entity
+          id:
+            name:
+              type: string
+            year:
+              type: integer
+
+Now you can use this entity:
+
+.. code-block:: php
+
+    <?php
+    namespace VehicleCatalogue\Model;
+
+    // $em is the EntityManager
+
+    $car = new Car("Audi A8", 2010);
+    $em->persist($car);
+    $em->flush();
+
+And for querying you can use arrays to both DQL and EntityRepositories:
+
+.. code-block:: php
+
+    <?php
+    namespace VehicleCatalogue\Model;
+
+    // $em is the EntityManager
+    $audi = $em->find("VehicleCatalogue\Model\Car", array("name" => "Audi A8", "year" => 2010));
+
+    $dql = "SELECT c FROM VehicleCatalogue\Model\Car c WHERE c.id = ?1";
+    $audi = $em->createQuery($dql)
+               ->setParameter(1, array("name" => "Audi A8", "year" => 2010))
+               ->getSingleResult();
+
+You can also use this entity in associations. Doctrine will then generate two foreign keys one for ``name``
+and to ``year`` to the related entities.
+
+.. note::
+
+    This example shows how you can nicely solve the requirement for exisiting
+    values before ``EntityManager#persist()``: By adding them as mandatory values for the constructor.
+
+Identity through foreign Entities
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. note::
+
+    Identity through foreign entities is only supported with Doctrine 2.1
+
+There are tons of use-cases where the identity of an Entity should be determined by the entity
+of one or many parent entities.
+
+-   Dynamic Attributes of an Entity (for example Article). Each Article has many
+    attributes with primary key "article_id" and "attribute_name".
+-   Address object of a Person, the primary key of the adress is "user_id". This is not a case of a composite primary
+    key, but the identity is derived through a foreign entity and a foreign key.
+-   Join Tables with metadata can be modelled as Entity, for example connections between two articles
+    with a little description and a score.
+
+The semantics of mapping identity through foreign entities are easy:
+
+-   Only allowed on Many-To-One or One-To-One associations.
+-   Plug an ``@Id`` annotation onto every assocation.
+-   Set an attribute ``association-key`` with the field name of the association in XML.
+-   Set a key ``associationKey:`` with the field name of the association in YAML.
+
+Use-Case 1: Dynamic Attributes
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+We keep up the example of an Article with arbitrary attributes, the mapping looks like this:
+
+.. code-block:: php
+
+    <?php
+    namespace Application\Model;
+
+    use Doctrine\Common\Collections\ArrayCollection;
+
+    /**
+     * @Entity
+     */
+    class Article
+    {
+        /** @Id @Column(type="integer") @GeneratedValue */
+        private $id;
+        /** @Column(type="string") */
+        private $title;
+
+        /**
+         * @OneToMany(targetEntity="ArticleAttribute", mappedBy="article", cascade={"ALL"}, indexBy="attribute")
+         */
+        private $attributes;
+
+        public function addAttribute($name, $value)
+        {
+            $this->attributes[$name] = new ArticleAttribute($name, $value, $this);
+        }
+    }
+
+    /**
+     * @Entity
+     */
+    class ArticleAttribute
+    {
+        /** @Id @ManyToOne(targetEntity="Article", inversedBy="attributes") */
+        private $article;
+
+        /** @Id @Column(type="string") */
+        private $attribute;
+
+        /** @Column(type="string") */
+        private $value;
+
+        public function __construct($name, $value, $article)
+        {
+            $this->attribute = $name;
+            $this->value = $value;
+            $this->article = $article;
+        }
+    }
+
+
+Use-Case 2: Simple Derived Identity
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+TODO
+
+Use-Case 3: Join-Table with Metadata
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+TODO
+
+Performance Considerations
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+TODO