doctrine2/en/tutorials/getting-started.rst

Getting Started
===============

Doctrine 2 is an object-relational mapper (ORM) for PHP 5.3.0+ that provides transparent persistence for PHP objects.
It uses the Data Mapper pattern at the heart of this project, aiming for a complete separation of
the domain/business logic from the persistence in a relational
database management system. The benefit of Doctrine for the
programmer is the ability to focus solely on the object-oriented business logic and
worry about persistence only as a secondary task. This doesn't mean
persistence is not important to Doctrine 2, however it is our
belief that there are considerable benefits for object-oriented
programming if persistence and entities are kept perfectly
separated.

.. note::

    The code of this tutorial is `available on Github <https://github.com/doctrine/doctrine2-orm-tutorial>`_.

What are Entities?
------------------

Entities are lightweight PHP Objects that don't need to extend any
abstract base class or interface. An entity class must not be final
or contain final methods. Additionally it must not implement
**clone** nor **wakeup** or :doc:`do so safely <../cookbook/implementing-wakeup-or-clone>`.

See the :doc:`architecture chapter <../reference/architecture>` for a full list of the restrictions
that your entities need to comply with.

An entity contains persistable properties. A persistable property
is an instance variable of the entity that is saved into and retrieved from the database
by Doctrine's data mapping capabilities.

An Example Model: Bug Tracker
-----------------------------

For this Getting Started Guide for Doctrine we will implement the
Bug Tracker domain model from the
`Zend\_Db\_Table <http://framework.zend.com/manual/en/zend.db.table.html>`_
documentation. Reading their documentation we can extract the
requirements to be:


-  A Bugs has a description, creation date, status, reporter and
   engineer
-  A bug can occur on different products (platforms)
-  Products have a name.
-  Bug Reporter and Engineers are both Users of the System.
-  A user can create new bugs.
-  The assigned engineer can close a bug.
-  A user can see all his reported or assigned bugs.
-  Bugs can be paginated through a list-view.

.. warning::

    This tutorial is incrementally building up your Doctrine 2
    knowledge and even lets you make some mistakes, to show some common
    pitfalls in mapping Entities to a database. Don't blindly
    copy-paste the examples here, it is not production ready without
    the additional comments and knowledge this tutorial teaches.

Setup Project
-------------

Make sure you get Doctrine from PEAR by calling the following commands
on your CLI:

::

    $ pear channel-discover pear.doctrine-project.org
    $ pear install --alldeps doctrine/DoctrineORM

This should install the packages DoctrineCommon, DoctrineDBAL, DoctrineORM,
SymfonyConsole and SymfonyYAML.

Now create a new directory for this tutorial project:

::

    $ mkdir project
    $ cd project

You can prepare the directory structure so that in the end it looks like:

::

    project
    |-- config
    |   |-- xml
    |   `-- yaml
    `-- entities

A first prototype
-----------------

A first simplified design for this domain model might look like the
following set of classes. Put them into `entities/Bug.php`,
`entities/Product.php` and `entities/User.php` respectively.

.. code-block:: php

    <?php
    // Bug.php
    class Bug
    {
        protected $id;
        protected $description;
        protected $created;
        protected $status;
    }

.. code-block:: php

    <?php
    // Product.php
    class Product
    {
        protected $id;
        protected $name;

        public function getId()
        {
            return $this->id;
        }

        public function getName()
        {
            return $this->name;
        }

        public function setName($name)
        {
            $this->name = $name;
        }
    }

.. code-block:: php

    // User.php
    class User
    {
        protected $id;
        public $name; // public for educational purpose, see below

        public function getId()
        {
            return $this->id;
        }

        public function getName()
        {
            return $this->name;
        }

        public function setName($name)
        {
            $this->name = $name;
        }
    }

.. warning::

    Properties should never be public when working when using Doctrine.
    This will lead to bugs with the way lazy loading works in Doctrine.

You see that all properties have getters and setters except `$id`.
Doctrine 2 uses Reflection to access the values in all your entities properties, so it
is possible to set the `$id` value for Doctrine, however not from
your application code. The use of reflection by Doctrine allows you
to completely encapsulate state and state changes in your entities.

Many of the fields are single scalar values, for example the 3 ID
fields of the entities, their names, description, status and change
dates. Doctrine 2 can easily handle these single values as can any
other ORM. From a point of our domain model they are ready to be
used right now and we will see at a later stage how they are mapped
to the database.

We will soon add references between objects in this domain
model. The semantics are discussed case by case to
explain how Doctrine handles them. In general each OneToOne or
ManyToOne Relation in the Database is replaced by an instance of
the related object in the domain model. Each OneToMany or
ManyToMany Relation is replaced by a collection of instances in the
domain model. You never have to work with the foreign keys, only
with objects that represent the foreign key through their own identity.

If you think this through carefully you realize Doctrine 2 will
load up the complete database in memory if you access one object.
However by default Doctrine generates Lazy Load proxies of entities
or collections of all the relations that haven't been explicitly
retrieved from the database yet.

To be able to use lazyload with collections, simple PHP arrays have
to be replaced by a generic collection interface for Doctrine which
tries to act as as much like an array as possible by using ArrayAccess,
IteratorAggregate and Countable interfaces. The class is the most
simple implementation of this interface.

Now that we know this, we have to clear up our domain model to cope
with the assumptions about related collections:

.. code-block:: php

    <?php
    // entities/Bug.php
    use Doctrine\Common\Collections\ArrayCollection;
    
    class Bug
    {
        // ... (previous code)

        protected $products = null;
    
        public function __construct()
        {
            $this->products = new ArrayCollection();
        }
    }

.. code-block:: php

    <?php
    // entities/User.php
    use Doctrine\Common\Collections\ArrayCollection;
    class User
    {
        // ... (previous code)

        protected $reportedBugs = null;
        protected $assignedBugs = null;
    
        public function __construct()
        {
            $this->reportedBugs = new ArrayCollection();
            $this->assignedBugs = new ArrayCollection();
        }
    }

Whenever an entity is recreated from the database, an Collection
implementation of the type Doctrine is injected into your entity
instead of an array. Compared to the ArrayCollection this
implementation helps the Doctrine ORM understand the changes that
have happened to the collection which are noteworthy for
persistence.

.. warning::

    Lazy load proxies always contain an instance of
    Doctrine's EntityManager and all its dependencies. Therefore a
    var\_dump() will possibly dump a very large recursive structure
    which is impossible to render and read. You have to use
    ``Doctrine\Common\Util\Debug::dump()`` to restrict the dumping to a
    human readable level. Additionally you should be aware that dumping
    the EntityManager to a Browser may take several minutes, and the
    Debug::dump() method just ignores any occurrences of it in Proxy
    instances.


Because we only work with collections for the references we must be
careful to implement a bidirectional reference in the domain model.
The concept of owning or inverse side of a relation is central to
this notion and should always be kept in mind. The following
assumptions are made about relations and have to be followed to be
able to work with Doctrine 2. These assumptions are not unique to
Doctrine 2 but are best practices in handling database relations
and Object-Relational Mapping.


-  Changes to Collections are saved or updated, when the entity on
   the *owning* side of the collection is saved or updated.
-  Saving an Entity at the inverse side of a relation never
   triggers a persist operation to changes to the collection.
-  In a one-to-one relation the entity holding the foreign key of
   the related entity on its own database table is *always* the owning
   side of the relation.
-  In a many-to-many relation, both sides can be the owning side of
   the relation. However in a bi-directional many-to-many relation
   only one is allowed to be.
-  In a many-to-one relation the Many-side is the owning side by
   default, because it holds the foreign key.
-  The OneToMany side of a relation is inverse by default, since
   the foreign key is saved on the Many side. A OneToMany relation can
   only be the owning side, if its implemented using a ManyToMany
   relation with join table and restricting the one side to allow only
   UNIQUE values per database constraint.

.. note::

    Consistency of bi-directional references on the inverse side of a
    relation have to be managed in userland application code. Doctrine
    cannot magically update your collections to be consistent.


In the case of Users and Bugs we have references back and forth to
the assigned and reported bugs from a user, making this relation
bi-directional. We have to change the code to ensure consistency of
the bi-directional reference:

.. code-block:: php

    <?php
    // entities/Bug.php
    class Bug
    {
        // ... (previous code)

        protected $engineer;
        protected $reporter;
    
        public function setEngineer($engineer)
        {
            $engineer->assignedToBug($this);
            $this->engineer = $engineer;
        }
    
        public function setReporter($reporter)
        {
            $reporter->addReportedBug($this);
            $this->reporter = $reporter;
        }
    
        public function getEngineer()
        {
            return $this->engineer;
        }
    
        public function getReporter()
        {
            return $this->reporter;
        }
    }

.. code-block:: php

    <?php
    // entities/User.php
    class User
    {
        // ... (previous code)

        protected $reportedBugs = null;
        protected $assignedBugs = null;

        public function addReportedBug($bug)
        {
            $this->reportedBugs[] = $bug;
        }
    
        public function assignedToBug($bug)
        {
            $this->assignedBugs[] = $bug;
        }
    }

I chose to name the inverse methods in past-tense, which should
indicate that the actual assigning has already taken place and the
methods are only used for ensuring consistency of the references.
This approach is my personal preference, you can choose whatever
method to make this work.

You can see from ``User::addReportedBug()`` and
``User::assignedToBug()`` that using this method in userland alone
would not add the Bug to the collection of the owning side in
``Bug::$reporter`` or ``Bug::$engineer``. Using these methods and
calling Doctrine for persistence would not update the collections
representation in the database.

Only using ``Bug::setEngineer()`` or ``Bug::setReporter()``
correctly saves the relation information. We also set both
collection instance variables to protected, however with PHP 5.3's
new features Doctrine is still able to use Reflection to set and
get values from protected and private properties.

The ``Bug::$reporter`` and ``Bug::$engineer`` properties are
Many-To-One relations, which point to a User. In a normalized
relational model the foreign key is saved on the Bug's table, hence
in our object-relation model the Bug is at the owning side of the
relation. You should always make sure that the use-cases of your
domain model should drive which side is an inverse or owning one in
your Doctrine mapping. In our example, whenever a new bug is saved
or an engineer is assigned to the bug, we don't want to update the
User to persist the reference, but the Bug. This is the case with
the Bug being at the owning side of the relation.

Bugs reference Products by an uni-directional ManyToMany relation in
the database that points from Bugs to Products.

.. code-block:: php

    <?php
    // entities/Bug.php
    class Bug
    {
        // ... (previous code)

        protected $products = null;
    
        public function assignToProduct($product)
        {
            $this->products[] = $product;
        }
    
        public function getProducts()
        {
            return $this->products;
        }
    }

We are now finished with the domain model given the requirements.
From the simple model with public properties only we had to do
quite some work to get to a model where we encapsulated the
references between the objects to make sure we don't break its
consistent state when using Doctrine.

However up to now the assumptions Doctrine imposed on our business
objects have not restricting us much in our domain modelling
capabilities. Actually we would have encapsulated access to all the
properties anyways by using object-oriented best-practices.

Metadata Mappings for our Entities
----------------------------------

Up to now we have only implemented our Entities as Data-Structures
without actually telling Doctrine how to persist them in the
database. If perfect in-memory databases would exist, we could now
finish the application using these entities by implementing code to
fulfil all the requirements. However the world isn't perfect and we
have to persist our entities in some storage to make sure we don't
loose their state. Doctrine currently serves Relational Database
Management Systems. In the future we are thinking to support NoSQL
vendors like CouchDb or MongoDb, however this is still far in the
future.

The next step for persistence with Doctrine is to describe the
structure of our domain model entities to Doctrine using a metadata
language. The metadata language describes how entities, their
properties and references should be persisted and what constraints
should be applied to them.

Metadata for entities are loaded using a
``Doctrine\ORM\Mapping\Driver\Driver`` implementation and Doctrine
2 already comes with XML, YAML and Annotations Drivers. This
Getting Started Guide will show the mappings for all Mapping Drivers.
References in the text will be made to the XML mapping.

Since we haven't namespaced our three entities, we have to
implement three mapping files called Bug.dcm.xml, Product.dcm.xml
and User.dcm.xml (or .yml) and put them into a distinct folder for mapping
configurations. For the annotations driver we need to use
doc-block comments on the entity classes themselves.

The first discussed definition will be for the Product, since it is
the most simple one:

.. configuration-block::

    .. code-block:: php

        <?php
        // entities/Product.php
        /**
         * @Entity @Table(name="products")
         **/
        class Product
        {
            /** @Id @Column(type="integer") @GeneratedValue **/
            protected $id;
            /** @Column(type="string") **/
            protected $name;

            // .. (other code)
        }

    .. code-block:: xml

        <!-- config/xml/Product.dcm.xml -->
        <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://doctrine-project.org/schemas/orm/doctrine-mapping.xsd">

              <entity name="Product" table="products">
                  <id name="id" type="integer">
                      <generator strategy="AUTO" />
                  </id>

                  <field name="name" type="string" />
              </entity>
        </doctrine-mapping>

    .. code-block:: yaml

        # config/yaml/Product.dcm.yml
        Product:
          type: entity
          table: products
          id:
            id:
              type: integer
              generator:
                strategy: AUTO
          fields:
            name:
              type: string

The top-level ``entity`` definition tag specifies information about
the class and table-name. The primitive type ``Product::$name`` is
defined as ``field`` attributes. The Id property is defined with
the ``id`` tag. The id has a ``generator`` tag nested inside which
defines that the primary key generation mechanism automatically
uses the database platforms native id generation strategy, for
example AUTO INCREMENT in the case of MySql or Sequences in the
case of PostgreSql and Oracle.

We then go on specifying the definition of a Bug:

.. configuration-block::
    .. code-block:: php

        <?php
        // entities/Bug.php
        /**
         * @Entity @Table(name="bugs")
         **/
        class Bug
        {
            /**
             * @Id @Column(type="integer") @GeneratedValue
             **/
            protected $id;
            /**
             * @Column(type="string")
             **/
            protected $description;
            /**
             * @Column(type="datetime")
             **/
            protected $created;
            /**
             * @Column(type="string")
             **/
            protected $status;

            /**
             * @ManyToOne(targetEntity="User", inversedBy="assignedBugs")
             **/
            protected $engineer;

            /**
             * @ManyToOne(targetEntity="User", inversedBy="reportedBugs")
             **/
            protected $reporter;

            /**
             * @ManyToMany(targetEntity="Product")
             **/
            protected $products;

            // ... (other code)
        }

    .. code-block:: xml

        <!-- config/xml/Bug.dcm.xml -->
        <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://doctrine-project.org/schemas/orm/doctrine-mapping.xsd">

            <entity name="Bug" table="bugs">
                <id name="id" type="integer">
                    <generator strategy="AUTO" />
                </id>

                <field name="description" type="text" />
                <field name="created" type="datetime" />
                <field name="status" type="string" />

                <many-to-one target-entity="User" field="reporter" inversed-by="reportedBugs" />
                <many-to-one target-entity="User" field="engineer" inversed-by="assignedBugs" />

                <many-to-many target-entity="Product" field="products" />
            </entity>
        </doctrine-mapping>

    .. code-block:: yaml

        # config/yaml/Bug.dcm.yml
        Bug:
          type: entity
          table: bugs
          id:
            id:
              type: integer
              generator:
                strategy: AUTO
          fields:
            description:
              type: text
            created:
              type: datetime
            status:
              type: string
          manyToOne:
            reporter:
              targetEntity: User
              inversedBy: reportedBugs
            engineer:
              targetEntity: User
              inversedBy: assignedBugs
          manyToMany:
            products:
              targetEntity: Product
              

Here again we have the entity, id and primitive type definitions.
The column names are used from the Zend\_Db\_Table examples and
have different names than the properties on the Bug class.
Additionally for the "created" field it is specified that it is of
the Type "DATETIME", which translates the YYYY-mm-dd HH:mm:ss
Database format into a PHP DateTime instance and back.

After the field definitions the two qualified references to the
user entity are defined. They are created by the ``many-to-one``
tag. The class name of the related entity has to be specified with
the ``target-entity`` attribute, which is enough information for
the database mapper to access the foreign-table. Since
``reporter`` and ``engineer`` are on the owning side of a
bi-directional relation we also have to specify the ``inversed-by``
attribute. They have to point to the field names on the inverse
side of the relationship. We will see in the next example that the ``inversed-by``
attribute has a counterpart ``mapped-by`` which makes that
the inverse side.

The last missing property is the ``Bug::$products`` collection. It
holds all products where the specific bug is occurring in. Again
you have to define the ``target-entity`` and ``field`` attributes
on the ``many-to-many`` tag. Furthermore you have to specify the
details of the many-to-many join-table and its foreign key columns.
The definition is rather complex, however relying on the XML
auto-completion I got it working easily, although I forget the
schema details all the time.

The last missing definition is that of the User entity:

.. configuration-block::

    .. code-block:: php

        <?php
        // entities/User.php
        /**
         * @Entity @Table(name="users")
         **/
        class User
        {
            /**
             * @Id @GeneratedValue @Column(type="integer")
             * @var int
             **/
            protected $id;

            /**
             * @Column(type="string")
             * @var string
             **/
            protected $name;

            /**
             * @OneToMany(targetEntity="Bug", mappedBy="reporter")
             * @var Bug[]
             **/
            protected $reportedBugs = null;

            /**
             * @OneToMany(targetEntity="Bug", mappedBy="engineer")
             * @var Bug[]
             **/
            protected $assignedBugs = null;

            // .. (other code)
        }

    .. code-block:: xml

        <!-- config/xml/User.dcm.xml -->
        <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://doctrine-project.org/schemas/orm/doctrine-mapping.xsd">

             <entity name="User" table="users">
                 <id name="id" type="integer">
                     <generator strategy="AUTO" />
                 </id>

                 <field name="name" type="string" />

                 <one-to-many target-entity="Bug" field="reportedBugs" mapped-by="reporter" />
                 <one-to-many target-entity="Bug" field="assignedBugs" mapped-by="engineer" />
             </entity>
        </doctrine-mapping>

    .. code-block:: yaml

        # config/xml/User.dcm.yml
        User:
          type: entity
          table: users
          id:
            id:
              type: integer
              generator:
                strategy: AUTO
          fields:
            name:
              type: string
          oneToMany:
            reportedBugs:
              targetEntity: Bug
              mappedBy: reporter
            assignedBugs:
              targetEntity: Bug
              mappedBy: engineer

Here are some new things to mention about the ``one-to-many`` tags.
Remember that we discussed about the inverse and owning side. Now
both reportedBugs and assignedBugs are inverse relations, which
means the join details have already been defined on the owning
side. Therefore we only have to specify the property on the Bug
class that holds the owning sides.

This example has a fair overview of the most basic features of the
metadata definition language.

Obtaining the EntityManager
---------------------------

Doctrine's public interface is the EntityManager, it provides the
access point to the complete lifecycle management of your entities
and transforms entities from and back to persistence. You have to
configure and create it to use your entities with Doctrine 2. I
will show the configuration steps and then discuss them step by
step:

.. code-block:: php

    <?php
    // bootstrap_doctrine.php

    // See :doc:`Configuration <../reference/configuration>` for up to date autoloading details.
    use Doctrine\ORM\Tools\Setup;

    require_once "Doctrine/ORM/Tools/Setup.php";
    Setup::registerAutoloadPEAR();

    // Create a simple "default" Doctrine ORM configuration for XML Mapping
    $isDevMode = true;
    $config = Setup::createXMLMetadataConfiguration(array(__DIR__."/config/xml"), $isDevMode);
    // or if you prefer yaml or annotations
    //$config = Setup::createAnnotationMetadataConfiguration(array(__DIR__."/entities"), $isDevMode);
    //$config = Setup::createYAMLMetadataConfiguration(array(__DIR__."/config/yaml"), $isDevMode);
    
    // database configuration parameters
    $conn = array(
        'driver' => 'pdo_sqlite',
        'path' => __DIR__ . '/db.sqlite',
    );
    
    // obtaining the entity manager
    $entityManager = \Doctrine\ORM\EntityManager::create($conn, $config);

The first block sets up the autoloading capabilities of Doctrine.
We assume here that you have installed Doctrine using PEAR.
See :doc:`Configuration <../reference/configuration>` for more details
on other installation procedures.

The second block consists of the instantiation of the ORM
Configuration object using the Setup helper. It assumes a bunch
of defaults that you don't have to bother about for now. You can
read up on the configuration details in the
:doc:`reference chapter on configuration <../reference/configuration>`.

The third block shows the configuration options required to connect
to a database, in my case a file-based sqlite database. All the
configuration options for all the shipped drivers are given in the
`DBAL Configuration section of the manual <http://www.doctrine-project.org/documentation/manual/2_0/en/dbal>`_.

You should make sure to make it configurable if Doctrine should run
in dev or production mode using the `$devMode` variable. You can
use an environment variable for example, hook into your frameworks configuration
or check for the HTTP_HOST of your devsystem (localhost for example)

.. code-block:: php

    <?php
    // examples, use your own logic to determine this:
    $isDevMode = ($_SERVER['HTTP_HOST'] == 'localhost');
    $isDevMode = ($_ENV['APPLICATION_ENV'] == 'development');

The last block shows how the ``EntityManager`` is obtained from a
factory method.

We also have to create a general bootstrap file for our application:

.. code-block:: php

    <?php
    // bootstrap.php

    require_once "entities/User.php";
    require_once "entities/Product.php";
    require_once "entities/Bug.php";

    if (!class_exists("Doctrine\Common\Version", false)) {
        require_once "bootstrap_doctrine.php";
    }

Generating the Database Schema
------------------------------

Now that we have defined the Metadata Mappings and bootstrapped the
EntityManager we want to generate the relational database schema
from it. Doctrine has a Command-Line-Interface that allows you to
access the SchemaTool, a component that generates the required
tables to work with the metadata.

For the command-line tool to work a cli-config.php file has to be
present in the project root directory, where you will execute the
doctrine command. Its a fairly simple file:

.. code-block:: php

    <?php
    // cli-config.php
    require_once "bootstrap.php";

    $helperSet = new \Symfony\Component\Console\Helper\HelperSet(array(
        'em' => new \Doctrine\ORM\Tools\Console\Helper\EntityManagerHelper($entityManager)
    ));

You can then change into your project directory and call the
Doctrine command-line tool:

::

    $ cd project/
    $ doctrine orm:schema-tool:create

.. note::

    The ``doctrine`` command will only be present if you installed
    Doctrine from PEAR. Otherwise you will have to dig into the
    ``bin/doctrine.php`` code of your Doctrine 2 directory to setup
    your doctrine command-line client.

    See the
    :doc:`Tools section of the manual <../reference/tools>`
    on how to setup the Doctrine console correctly.


During the development you probably need to re-create the database
several times when changing the Entity metadata. You can then
either re-create the database:

::

    $ doctrine orm:schema-tool:drop --force
    $ doctrine orm:schema-tool:create

Or use the update functionality:

::

    $ doctrine orm:schema-tool:update --force

The updating of databases uses a Diff Algorithm for a given
Database Schema, a cornerstone of the ``Doctrine\DBAL`` package,
which can even be used without the Doctrine ORM package. However
its not available in SQLite since it does not support ALTER TABLE.

Writing Entities into the Database
----------------------------------

.. note::

    This tutorial assumes you call all the example scripts from the CLI.

Having created the schema we can now start and save entities in the
database. For starters we need a create user use-case:

.. code-block:: php

    <?php
    // create_user.php
    require_once "bootstrap.php";

    $newUsername = $argv[1];
    
    $user = new User();
    $user->setName($newUsername);
    
    $entityManager->persist($user);
    $entityManager->flush();

    echo "Created User with ID " . $user->getId() . "\n";

Products can also be created:

.. code-block:: php

    <?php
    // create_product.php
    require_once "bootstrap.php";

    $newProductName = $argv[1];
    
    $product = new Product();
    $product->setName($newProductName);
    
    $entityManager->persist($product);
    $entityManager->flush();

    echo "Created Product with ID " . $product->getId() . "\n";

Now call:

::

    $ php create_user.php beberlei
    $ php create_product.php MyProduct

So what is happening in those two snippets? In both examples the
code that works on User and Product is pretty standard OOP. The interesting bits are the
communication with the ``EntityManager``. To notify the
EntityManager that a new entity should be inserted into the
database you have to call ``persist()``. However the EntityManager
does not act on this command, its merely notified. You have to explicitly
call ``flush()`` to have the EntityManager write those two entities
to the database.

You might wonder why does this distinction between persist
notification and flush exist: Doctrine 2 uses the UnitOfWork
pattern to aggregate all writes (INSERT, UDPATE, DELETE) into one
single transaction, which is executed when flush is called.
Using this approach the write-performance is significantly better
than in a scenario where updates are done for each entity in
isolation. In more complex scenarios than the previous two, you are
free to request updates on many different entities and all flush
them at once.

Doctrine's UnitOfWork detects entities that have changed after
retrieval from the database automatically when the flush operation
is called, so that you only have to keep track of those entities
that are new or to be removed and pass them to
``EntityManager#persist()`` and ``EntityManager#remove()``
respectively.

We are now getting to the "Create a New Bug" requirement and the
code for this scenario may look like this:

.. code-block:: php

    <?php
    // create_bug.php
    require_once "bootstrap.php";

    $theReporterId = $argv[1];
    $theDefaultEngineerId = $argv[1];
    $productIds = explode(",", $argv[3]);

    $reporter = $entityManager->find("User", $theReporterId);
    $engineer = $entityManager->find("User", $theDefaultEngineerId);
    if (!$reporter || !$engineer) {
        echo "No reporter and/or engineer found for the input.\n";
        exit(1);
    }
    
    $bug = new Bug();
    $bug->setDescription("Something does not work!");
    $bug->setCreated(new DateTime("now"));
    $bug->setStatus("OPEN");
    
    foreach ($productIds AS $productId) {
        $product = $entityManager->find("Product", $productId);
        $bug->assignToProduct($product);
    }
    
    $bug->setReporter($reporter);
    $bug->setEngineer($engineer);
    
    $entityManager->persist($bug);
    $entityManager->flush();
    
    echo "Your new Bug Id: ".$bug->getId()."\n";

Since we only have one user and product, probably with the ID of 1, we can call this script with:

::

    php create_bug.php 1 1 1

This is the first contact with the read API of the EntityManager,
showing that a call to ``EntityManager#find($name, $id)`` returns a
single instance of an entity queried by primary key. Besides this
we see the persist + flush pattern again to save the Bug into the
database.

See how simple relating Bug, Reporter, Engineer and Products is
done by using the discussed methods in the "A first prototype"
section. The UnitOfWork will detect this relations when flush is
called and relate them in the database appropriately.

Queries for Application Use-Cases
---------------------------------

List of Bugs
~~~~~~~~~~~~

Using the previous examples we can fill up the database quite a
bit, however we now need to discuss how to query the underlying
mapper for the required view representations. When opening the
application, bugs can be paginated through a list-view, which is
the first read-only use-case:

.. code-block:: php

    <?php
    // list_bugs.php
    require_once "bootstrap.php";

    $dql = "SELECT b, e, r FROM Bug b JOIN b.engineer e JOIN b.reporter r ORDER BY b.created DESC";
    
    $query = $entityManager->createQuery($dql);
    $query->setMaxResults(30);
    $bugs = $query->getResult();
    
    foreach($bugs AS $bug) {
        echo $bug->getDescription()." - ".$bug->getCreated()->format('d.m.Y')."\n";
        echo "    Reported by: ".$bug->getReporter()->name."\n";
        echo "    Assigned to: ".$bug->getEngineer()->name."\n";
        foreach($bug->getProducts() AS $product) {
            echo "    Platform: ".$product->name."\n";
        }
        echo "\n";
    }

The DQL Query in this example fetches the 30 most recent bugs with
their respective engineer and reporter in one single SQL statement.
The console output of this script is then:

::

    Something does not work! - 02.04.2010
        Reported by: beberlei
        Assigned to: beberlei
        Platform: My Product

.. note::

    **Dql is not Sql**

    You may wonder why we start writing SQL at the beginning of this
    use-case. Don't we use an ORM to get rid of all the endless
    hand-writing of SQL? Doctrine introduces DQL which is best
    described as **object-query-language** and is a dialect of
    `OQL <http://en.wikipedia.org/wiki/Object_Query_Language>`_ and
    similar to `HQL <http://www.hibernate.org>`_ or
    `JPQL <http://en.wikipedia.org/wiki/Java_Persistence_Query_Language>`_.
    It does not know the concept of columns and tables, but only those
    of Entity-Class and property. Using the Metadata we defined before
    it allows for very short distinctive and powerful queries.

    An important reason why DQL is favourable to the Query API of most
    ORMs is its similarity to SQL. The DQL language allows query
    constructs that most ORMs don't, GROUP BY even with HAVING,
    Sub-selects, Fetch-Joins of nested classes, mixed results with
    entities and scalar data such as COUNT() results and much more.
    Using DQL you should seldom come to the point where you want to
    throw your ORM into the dumpster, because it doesn't support some
    the more powerful SQL concepts.

    Besides handwriting DQL you can however also use the
    ``QueryBuilder`` retrieved by calling
    ``$entityManager->createQueryBuilder()`` which is a Query Object
    around the DQL language.

    As a last resort you can however also use Native SQL and a
    description of the result set to retrieve entities from the
    database. DQL boils down to a Native SQL statement and a
    ``ResultSetMapping`` instance itself. Using Native SQL you could
    even use stored procedures for data retrieval, or make use of
    advanced non-portable database queries like PostgreSql's recursive
    queries.


Array Hydration of the Bug List
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

In the previous use-case we retrieved the result as their
respective object instances. We are not limited to retrieving
objects only from Doctrine however. For a simple list view like the
previous one we only need read access to our entities and can
switch the hydration from objects to simple PHP arrays instead.
This can obviously yield considerable performance benefits for
read-only requests.

Implementing the same list view as before using array hydration we
can rewrite our code:

.. code-block:: php

    <?php
    // list_bugs_array.php
    require_once "bootstrap.php";

    $dql = "SELECT b, e, r, p FROM Bug b JOIN b.engineer e ".
           "JOIN b.reporter r JOIN b.products p ORDER BY b.created DESC";
    $query = $entityManager->createQuery($dql);
    $bugs = $query->getArrayResult();
    
    foreach ($bugs AS $bug) {
        echo $bug['description'] . " - " . $bug['created']->format('d.m.Y')."\n";
        echo "    Reported by: ".$bug['reporter']['name']."\n";
        echo "    Assigned to: ".$bug['engineer']['name']."\n";
        foreach($bug['products'] AS $product) {
            echo "    Platform: ".$product['name']."\n";
        }
        echo "\n";
    }

There is one significant difference in the DQL query however, we
have to add an additional fetch-join for the products connected to
a bug. The resulting SQL query for this single select statement is
pretty large, however still more efficient to retrieve compared to
hydrating objects.

Find by Primary Key
~~~~~~~~~~~~~~~~~~~

The next Use-Case is displaying a Bug by primary key. This could be
done using DQL as in the previous example with a where clause,
however there is a convenience method on the Entity Manager that
handles loading by primary key, which we have already seen in the
write scenarios:

However we will soon see another problem with our entities using
this approach. Try displaying the engineer's name:

.. code-block:: php

    <?php
    // show_bug.php
    require_once "bootstrap.php";

    $theBugId = $argv[1];

    $bug = $entityManager->find("Bug", (int)$theBugId);

    echo "Bug: ".$bug->getDescription()."\n";
    // Accessing our special public $name property here on purpose:
    echo "Engineer: ".$bug->getEngineer()->name."\n";

The output of the engineers name is null! What is happening?
It worked in the previous example, so it can't be a problem with the persistence code of
Doctrine. What is it then? You walked in the public property trap.

Since we only retrieved the bug by primary key both the engineer
and reporter are not immediately loaded from the database but are
replaced by LazyLoading proxies. Sample code of this proxy
generated code can be found in the specified Proxy Directory, it
looks like:

.. code-block:: php

    <?php
    namespace MyProject\Proxies;
    
    /**
     * THIS CLASS WAS GENERATED BY THE DOCTRINE ORM. DO NOT EDIT THIS FILE.
     **/
    class UserProxy extends \User implements \Doctrine\ORM\Proxy\Proxy
    {
        // .. lazy load code here
    
        public function addReportedBug($bug)
        {
            $this->_load();
            return parent::addReportedBug($bug);
        }
    
        public function assignedToBug($bug)
        {
            $this->_load();
            return parent::assignedToBug($bug);
        }
    }

See how upon each method call the proxy is lazily loaded from the
database? Using public properties however we never call a method
and Doctrine has no way to hook into the PHP Engine to detect a
direct access to a public property and trigger the lazy load. We
need to rewrite our entities, make all the properties private or
protected and add getters and setters to get a working example:

.. code-block:: php

    <?php
    // show_bug.php
    require_once "bootstrap.php";

    $theBugId = $argv[1];

    $bug = $entityManager->find("Bug", (int)$theBugId);

    echo "Bug: ".$bug->getDescription()."\n";
    echo "Engineer: ".$bug->getEngineer()->getName()."\n";

Now prints:

::

    $ php show_bug.php 1
    Bug: Something does not work!
    Engineer: beberlei

Being required to use private or protected properties Doctrine 2
actually enforces you to encapsulate your objects according to
object-oriented best-practices.

Dashboard of the User
---------------------

For the next use-case we want to retrieve the dashboard view, a
list of all open bugs the user reported or was assigned to. This
will be achieved using DQL again, this time with some WHERE clauses
and usage of bound parameters:

.. code-block:: php

    <?php
    // dashboard.php
    require_once "bootstrap.php";

    $theUserId = $argv[1];

    $dql = "SELECT b, e, r FROM Bug b JOIN b.engineer e JOIN b.reporter r ".
           "WHERE b.status = 'OPEN' AND (e.id = ?1 OR r.id = ?1) ORDER BY b.created DESC";
    
    $myBugs = $entityManager->createQuery($dql)
                            ->setParameter(1, $theUserId)
                            ->setMaxResults(15)
                            ->getResult();
    
    echo "You have created or assigned to " . count($myBugs) . " open bugs:\n\n";

    foreach ($myBugs AS $bug) {
        echo $bug->getId() . " - " . $bug->getDescription()."\n";
    }

Number of Bugs
--------------

Until now we only retrieved entities or their array representation.
Doctrine also supports the retrieval of non-entities through DQL.
These values are called "scalar result values" and may even be
aggregate values using COUNT, SUM, MIN, MAX or AVG functions.

We will need this knowledge to retrieve the number of open bugs
grouped by product:

.. code-block:: php

    <?php
    // products.php
    require_once "bootstrap.php";

    $dql = "SELECT p.id, p.name, count(b.id) AS openBugs FROM Bug b ".
           "JOIN b.products p WHERE b.status = 'OPEN' GROUP BY p.id";
    $productBugs = $entityManager->createQuery($dql)->getScalarResult();
    
    foreach($productBugs as $productBug) {
        echo $productBug['name']." has " . $productBug['openBugs'] . " open bugs!\n";
    }

Updating Entities
-----------------

There is a single use-case missing from the requirements, Engineers
should be able to close a bug. This looks like:

.. code-block:: php

    <?php
    // entities/Bug.php

    class Bug
    {
        public function close()
        {
            $this->status = "CLOSE";
        }
    }

.. code-block:: php

    <?php
    // close_bug.php
    require_once "bootstrap.php";

    $theBugId = $argv[1];

    $bug = $entityManager->find("Bug", (int)$theBugId);
    $bug->close();
    
    $entityManager->flush();

When retrieving the Bug from the database it is inserted into the
IdentityMap inside the UnitOfWork of Doctrine. This means your Bug
with exactly this id can only exist once during the whole request
no matter how often you call ``EntityManager#find()``. It even
detects entities that are hydrated using DQL and are already
present in the Identity Map.

When flush is called the EntityManager loops over all the entities
in the identity map and performs a comparison between the values
originally retrieved from the database and those values the entity
currently has. If at least one of these properties is different the
entity is scheduled for an UPDATE against the database. Only the
changed columns are updated, which offers a pretty good performance
improvement compared to updating all the properties.

Entity Repositories
-------------------

For now we have not discussed how to separate the Doctrine query logic from your model.
In Doctrine 1 there was the concept of ``Doctrine_Table`` instances for this
seperation. The similar concept in Doctrine2 is called Entity Repositories, integrating
the `repository pattern <http://martinfowler.com/eaaCatalog/repository.html>`_ at the heart of Doctrine.

Every Entity uses a default repository by default and offers a bunch of convenience
methods that you can use to query for instances of that Entity. Take for example
our Product entity. If we wanted to Query by name, we can use:

.. code-block:: php

    <?php
    $product = $entityManager->getRepository('Product')
                             ->findOneBy(array('name' => $productName));

The method ``findOneBy()`` takes an array of fields or association keys and the values to match against.

If you want to find all entities matching a condition you can use ``findBy()``, for
example querying for all closed bugs:

.. code-block:: php

    <?php
    $bugs = $entityManager->getRepository('Bug')
                          ->findBy(array('status' => 'CLOSED'));

    foreach ($bugs AS $bug) {
        // do stuff
    }

Compared to DQL these query methods are falling short of functionality very fast.
Doctrine offers you a convenient way to extend the functionalities of the default ``EntityRepository``
and put all the specialized DQL query logic on it. For this you have to create a subclass
of ``Doctrine\ORM\EntityRepository``, in our case a ``BugRepository`` and group all
the previoiusly discussed query functionality in it:

.. code-block:: php

    <?php
    // repositories/BugRepository.php

    use Doctrine\ORM\EntityRepository;

    class BugRepository extends EntityRepository
    {
        public function getRecentBugs($number = 30)
        {
            $dql = "SELECT b, e, r FROM Bug b JOIN b.engineer e JOIN b.reporter r ORDER BY b.created DESC";

            $query = $this->getEntityManager()->createQuery($dql);
            $query->setMaxResults($number);
            return $query->getResult();
        }

        public function getRecentBugsArray($number = 30)
        {
            $dql = "SELECT b, e, r, p FROM Bug b JOIN b.engineer e ".
                   "JOIN b.reporter r JOIN b.products p ORDER BY b.created DESC";
            $query = $this->getEntityManager()->createQuery($dql);
            $query->setMaxResults($number);
            return $query->getArrayResult();
        }

        public function getUsersBugs($userId, $number = 15)
        {
            $dql = "SELECT b, e, r FROM Bug b JOIN b.engineer e JOIN b.reporter r ".
                   "WHERE b.status = 'OPEN' AND e.id = ?1 OR r.id = ?1 ORDER BY b.created DESC";

            return $this->getEntityManager()->createQuery($dql)
                                 ->setParameter(1, $userId)
                                 ->setMaxResults($number)
                                 ->getResult();
        }

        public function getOpenBugsByProduct()
        {
            $dql = "SELECT p.id, p.name, count(b.id) AS openBugs FROM Bug b ".
                   "JOIN b.products p WHERE b.status = 'OPEN' GROUP BY p.id";
            return $this->getEntityManager()->createQuery($dql)->getScalarResult();
        }
    }

Dont forget to add a `require_once` call for this class to the bootstrap.php

To be able to use this query logic through ``$this->getEntityManager()->getRepository('Bug')``
we have to adjust the metadata slightly.

.. configuration-block::

    .. code-block:: php

        <?php
        /**
         * @Entity(repositoryClass="BugRepository")
         * @Table(name="bugs")
         **/
        class Bug
        {
            //...
        }

    .. code-block:: xml

        <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://doctrine-project.org/schemas/orm/doctrine-mapping.xsd">

              <entity name="Bug" table="bugs" repository-class="BugRepository">

              </entity>
        </doctrine-mapping>

    .. code-block:: yaml

        Bug:
          type: entity
          repositoryClass: BugRepository

Now we can remove our query logic in all the places and instead use them through the EntityRepository.
As an example here is the code of the first use case "List of Bugs":

.. code-block:: php

    <?php
    // list_bugs_repository.php
    require_once "bootstrap.php";

    $bugs = $entityManager->getRepository('Bug')->getRecentBugs();

    foreach($bugs AS $bug) {
        echo $bug->getDescription()." - ".$bug->getCreated()->format('d.m.Y')."\n";
        echo "    Reported by: ".$bug->getReporter()->getName()."\n";
        echo "    Assigned to: ".$bug->getEngineer()->getName()."\n";
        foreach($bug->getProducts() AS $product) {
            echo "    Platform: ".$product->getName()."\n";
        }
        echo "\n";
    }

Using EntityRepositories you can avoid coupling your model with specific query logic.
You can also re-use query logic easily throughout your application.

Conclusion
----------

This tutorial is over here, I hope you had fun. Additional content
will be added to this tutorial incrementally, topics will include:

-   More on Association Mappings
-   Lifecycle Events triggered in the UnitOfWork
-   Ordering of Collections

Additional details on all the topics discussed here can be found in
the respective manual chapters.