Databases and Doctrine

Databases and Doctrine

One of the most common and challenging tasks for any application involves persisting and reading information to and from a database. Although the Symfony full-stack Framework doesn't integrate any ORM by default, the Symfony Standard Edition, which is the most widely used distribution, comes integrated with Doctrine, a library whose sole goal is to give you powerful tools to make this easy. In this chapter, you'll learn the basic philosophy behind Doctrine and see how easy working with a database can be.

Note

Doctrine is totally decoupled from Symfony and using it is optional. This chapter is all about the Doctrine ORM, which aims to let you map objects to a relational database (such as MySQL, PostgreSQL or Microsoft SQL). If you prefer to use raw database queries, this is easy, and explained in the "How to Use Doctrine DBAL" cookbook entry.

You can also persist data to MongoDB using Doctrine ODM library. For more information, read the "DoctrineMongoDBBundle" documentation.

A Simple Example: A Product

The easiest way to understand how Doctrine works is to see it in action. In this section, you'll configure your database, create a Product object, persist it to the database and fetch it back out.

Configuring the Database

Before you really begin, you'll need to configure your database connection information. By convention, this information is usually configured in an app/config/parameters.yml file:

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# app/config/parameters.yml
parameters:
    database_driver:    pdo_mysql
    database_host:      localhost
    database_name:      test_project
    database_user:      root
    database_password:  password

# ...

Note

Defining the configuration via parameters.yml is just a convention. The parameters defined in that file are referenced by the main configuration file when setting up Doctrine:

  • YAML
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    # app/config/config.yml
    doctrine:
        dbal:
            driver:   '%database_driver%'
            host:     '%database_host%'
            dbname:   '%database_name%'
            user:     '%database_user%'
            password: '%database_password%'
    
  • XML
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    <!-- app/config/config.xml -->
    <?xml version="1.0" encoding="UTF-8" ?>
    <container xmlns="http://symfony.com/schema/dic/services"
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xmlns:doctrine="http://symfony.com/schema/dic/doctrine"
        xsi:schemaLocation="http://symfony.com/schema/dic/services
            http://symfony.com/schema/dic/services/services-1.0.xsd
            http://symfony.com/schema/dic/doctrine
            http://symfony.com/schema/dic/doctrine/doctrine-1.0.xsd">
    
        <doctrine:config>
            <doctrine:dbal
                driver="%database_driver%"
                host="%database_host%"
                dbname="%database_name%"
                user="%database_user%"
                password="%database_password%" />
        </doctrine:config>
    </container>
    
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    // app/config/config.php
    $configuration->loadFromExtension('doctrine', array(
        'dbal' => array(
            'driver'   => '%database_driver%',
            'host'     => '%database_host%',
            'dbname'   => '%database_name%',
            'user'     => '%database_user%',
            'password' => '%database_password%',
        ),
    ));
    

By separating the database information into a separate file, you can easily keep different versions of the file on each server. You can also easily store database configuration (or any sensitive information) outside of your project, like inside your Apache configuration, for example. For more information, see How to Set external Parameters in the Service Container.

Now that Doctrine can connect to your database, the following command can automatically generate an empty test_project database for you:

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$ php bin/console doctrine:database:create

One mistake even seasoned developers make when starting a Symfony project is forgetting to set up default charset and collation on their database, ending up with latin type collations, which are default for most databases. They might even remember to do it the very first time, but forget that it's all gone after running a relatively common command during development:

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$ php bin/console doctrine:database:drop --force
$ php bin/console doctrine:database:create

Setting UTF8 defaults for MySQL is as simple as adding a few lines to your configuration file (typically my.cnf):

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[mysqld]
# Version 5.5.3 introduced "utf8mb4", which is recommended
collation-server     = utf8mb4_general_ci # Replaces utf8_general_ci
character-set-server = utf8mb4            # Replaces utf8

You can also change the defaults for Doctrine so that the generated SQL uses the correct character set.

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    # app/config/config.yml
    doctrine:
        dbal:
            charset: utf8mb4
            default_table_options:
                charset: utf8mb4
                collate: utf8mb4_unicode_ci
    
  • XML
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    <!-- app/config/config.xml -->
    <?xml version="1.0" encoding="UTF-8" ?>
    <container xmlns="http://symfony.com/schema/dic/services"
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xmlns:doctrine="http://symfony.com/schema/dic/doctrine"
        xsi:schemaLocation="http://symfony.com/schema/dic/services
            http://symfony.com/schema/dic/services/services-1.0.xsd
            http://symfony.com/schema/dic/doctrine
            http://symfony.com/schema/dic/doctrine/doctrine-1.0.xsd">
    
        <doctrine:config>
            <doctrine:dbal
                charset="utf8mb4">
                    <doctrine:default-table-option name="charset">utf8mb4</doctrine:default-table-option>
                    <doctrine:default-table-option name="collate">utf8mb4_unicode_ci</doctrine:default-table-option>
            </doctrine:dbal>
        </doctrine:config>
    </container>
    
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    // app/config/config.php
    $configuration->loadFromExtension('doctrine', array(
        'dbal' => array(
            'charset' => 'utf8mb4',
            'default_table_options' => array(
                'charset' => 'utf8mb4'
                'collate' => 'utf8mb4_unicode_ci'
            )
        ),
    ));
    

We recommend against MySQL's utf8 character set, since it does not support 4-byte unicode characters, and strings containing them will be truncated. This is fixed by the newer utf8mb4 character set.

Note

If you want to use SQLite as your database, you need to set the path where your database file should be stored:

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    # app/config/config.yml
    doctrine:
        dbal:
            driver: pdo_sqlite
            path: '%kernel.root_dir%/sqlite.db'
            charset: UTF8
    
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    <!-- app/config/config.xml -->
    <?xml version="1.0" encoding="UTF-8" ?>
    <container xmlns="http://symfony.com/schema/dic/services"
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xmlns:doctrine="http://symfony.com/schema/dic/doctrine"
        xsi:schemaLocation="http://symfony.com/schema/dic/services
            http://symfony.com/schema/dic/services/services-1.0.xsd
            http://symfony.com/schema/dic/doctrine
            http://symfony.com/schema/dic/doctrine/doctrine-1.0.xsd">
    
        <doctrine:config>
            <doctrine:dbal
                driver="pdo_sqlite"
                path="%kernel.root_dir%/sqlite.db"
                charset="UTF-8" />
        </doctrine:config>
    </container>
    
  • PHP
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    // app/config/config.php
    $container->loadFromExtension('doctrine', array(
        'dbal' => array(
            'driver'  => 'pdo_sqlite',
            'path'    => '%kernel.root_dir%/sqlite.db',
            'charset' => 'UTF-8',
        ),
    ));
    

Creating an Entity Class

Suppose you're building an application where products need to be displayed. Without even thinking about Doctrine or databases, you already know that you need a Product object to represent those products. Create this class inside the Entity directory of your AppBundle:

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// src/AppBundle/Entity/Product.php
namespace AppBundle\Entity;

class Product
{
    private $name;
    private $price;
    private $description;
}

The class - often called an "entity", meaning a basic class that holds data - is simple and helps fulfill the business requirement of needing products in your application. This class can't be persisted to a database yet - it's just a simple PHP class.

Tip

Once you learn the concepts behind Doctrine, you can have Doctrine create simple entity classes for you. This will ask you interactive questions to help you build any entity:

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$ php bin/console doctrine:generate:entity

Add Mapping Information

Doctrine allows you to work with databases in a much more interesting way than just fetching rows of scalar data into an array. Instead, Doctrine allows you to fetch entire objects out of the database, and to persist entire objects to the database. For Doctrine to be able to do this, you must map your database tables to specific PHP classes, and the columns on those tables must be mapped to specific properties on their corresponding PHP classes.

../_images/doctrine_image_1.png

You'll provide this mapping information in the form of "metadata", a collection of rules that tells Doctrine exactly how the Product class and its properties should be mapped to a specific database table. This metadata can be specified in a number of different formats, including YAML, XML or directly inside the Product class via DocBlock annotations:

  • Annotations
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    // src/AppBundle/Entity/Product.php
    namespace AppBundle\Entity;
    
    use Doctrine\ORM\Mapping as ORM;
    
    /**
     * @ORM\Entity
     * @ORM\Table(name="product")
     */
    class Product
    {
        /**
         * @ORM\Column(type="integer")
         * @ORM\Id
         * @ORM\GeneratedValue(strategy="AUTO")
         */
        private $id;
    
        /**
         * @ORM\Column(type="string", length=100)
         */
        private $name;
    
        /**
         * @ORM\Column(type="decimal", scale=2)
         */
        private $price;
    
        /**
         * @ORM\Column(type="text")
         */
        private $description;
    }
    
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    # src/AppBundle/Resources/config/doctrine/Product.orm.yml
    AppBundle\Entity\Product:
        type: entity
        table: product
        id:
            id:
                type: integer
                generator: { strategy: AUTO }
        fields:
            name:
                type: string
                length: 100
            price:
                type: decimal
                scale: 2
            description:
                type: text
    
  • XML
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    <!-- src/AppBundle/Resources/config/doctrine/Product.orm.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://doctrine-project.org/schemas/orm/doctrine-mapping.xsd">
    
        <entity name="AppBundle\Entity\Product" table="product">
            <id name="id" type="integer">
                <generator strategy="AUTO" />
            </id>
            <field name="name" type="string" length="100" />
            <field name="price" type="decimal" scale="2" />
            <field name="description" type="text" />
        </entity>
    </doctrine-mapping>
    

Note

A bundle can accept only one metadata definition format. For example, it's not possible to mix YAML metadata definitions with annotated PHP entity class definitions.

Tip

The table name is optional and if omitted, will be determined automatically based on the name of the entity class.

Doctrine allows you to choose from a wide variety of different field types, each with their own options. For information on the available field types, see the Doctrine Field Types Reference section.

You can also check out Doctrine's Basic Mapping Documentation for all details about mapping information. If you use annotations, you'll need to prepend all annotations with ORM\ (e.g. ORM\Column(...)), which is not shown in Doctrine's documentation. You'll also need to include the use Doctrine\ORM\Mapping as ORM; statement, which imports the ORM annotations prefix.

Caution

Be careful if the names of your entity classes (or their properties) are also reserved SQL keywords like GROUP or USER. For example, if your entity's class name is Group, then, by default, the corresponding table name would be group. This will cause an SQL error in some database engines. See Doctrine's Reserved SQL keywords documentation for details on how to properly escape these names. Alternatively, if you're free to choose your database schema, simply map to a different table name or column name. See Doctrine's Creating Classes for the Database and Property Mapping documentation.

Note

When using another library or program (e.g. Doxygen) that uses annotations, you should place the @IgnoreAnnotation annotation on the class to indicate which annotations Symfony should ignore.

For example, to prevent the @fn annotation from throwing an exception, add the following:

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/**
 * @IgnoreAnnotation("fn")
 */
class Product
// ...

Generating Getters and Setters

Even though Doctrine now knows how to persist a Product object to the database, the class itself isn't really useful yet. Since Product is just a regular PHP class with private properties, you need to create public getter and setter methods (e.g. getName(), setName($name)) in order to access its properties in the rest of your application's code. Fortunately, the following command can generate these boilerplate methods automatically:

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$ php bin/console doctrine:generate:entities AppBundle/Entity/Product

This command makes sure that all the getters and setters are generated for the Product class. This is a safe command - you can run it over and over again: it only generates getters and setters that don't exist (i.e. it doesn't replace your existing methods).

Caution

Keep in mind that Doctrine's entity generator produces simple getters/setters. You should review the generated methods and add any logic, if necessary, to suit the needs of your application.

With the doctrine:generate:entities command you can:

  • generate getter and setter methods in entity classes;
  • generate repository classes on behalf of entities configured with the @ORM\Entity(repositoryClass="...") annotation;
  • generate the appropriate constructor for 1:n and n:m relations.

The doctrine:generate:entities command saves a backup of the original Product.php named Product.php~. In some cases, the presence of this file can cause a "Cannot redeclare class" error. It can be safely removed. You can also use the --no-backup option to prevent generating these backup files.

Note that you don't need to use this command. You could also write the necessary getters and setters by hand. This option simply exists to save you time, since creating these methods is often a common task during development.

You can also generate all known entities (i.e. any PHP class with Doctrine mapping information) of a bundle or an entire namespace:

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# generates all entities in the AppBundle
$ php bin/console doctrine:generate:entities AppBundle

# generates all entities of bundles in the Acme namespace
$ php bin/console doctrine:generate:entities Acme

Creating the Database Tables/Schema

You now have a usable Product class with mapping information so that Doctrine knows exactly how to persist it. Of course, you don't yet have the corresponding product table in your database. Fortunately, Doctrine can automatically create all the database tables needed for every known entity in your application. To do this, run:

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$ php bin/console doctrine:schema:update --force

Tip

Actually, this command is incredibly powerful. It compares what your database should look like (based on the mapping information of your entities) with how it actually looks, and executes the SQL statements needed to update the database schema to where it should be. In other words, if you add a new property with mapping metadata to Product and run this task, it will execute the "ALTER TABLE" statement needed to add that new column to the existing product table.

An even better way to take advantage of this functionality is via migrations, which allow you to generate these SQL statements and store them in migration classes that can be run systematically on your production server in order to update and track changes to your database schema safely and reliably.

Whether or not you take advantage of migrations, the doctrine:schema:update command should only be used during development. It should not be used in a production environment.

Your database now has a fully-functional product table with columns that match the metadata you've specified.

Persisting Objects to the Database

Now that you have mapped the Product entity to its corresponding product table, you're ready to persist Product objects to the database. From inside a controller, this is pretty easy. Add the following method to the DefaultController of the bundle:

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// src/AppBundle/Controller/DefaultController.php

// ...
use AppBundle\Entity\Product;
use Symfony\Component\HttpFoundation\Response;

// ...
public function createAction()
{
    $product = new Product();
    $product->setName('Keyboard');
    $product->setPrice(19.99);
    $product->setDescription('Ergonomic and stylish!');

    $em = $this->getDoctrine()->getManager();

    // tells Doctrine you want to (eventually) save the Product (no queries yet)
    $em->persist($product);

    // actually executes the queries (i.e. the INSERT query)
    $em->flush();

    return new Response('Saved new product with id '.$product->getId());
}

Note

If you're following along with this example, you'll need to create a route that points to this action to see it work.

Tip

This article shows working with Doctrine from within a controller by using the getDoctrine() method of the controller. This method is a shortcut to get the doctrine service. You can work with Doctrine anywhere else by injecting that service in the service. See Service Container for more on creating your own services.

Take a look at the previous example in more detail:

  • lines 10-13 In this section, you instantiate and work with the $product object like any other normal PHP object.
  • line 15 This line fetches Doctrine's entity manager object, which is responsible for the process of persisting objects to, and fetching objects from, the database.
  • line 17 The persist($product) call tells Doctrine to "manage" the $product object. This does not cause a query to be made to the database.
  • line 18 When the flush() method is called, Doctrine looks through all of the objects that it's managing to see if they need to be persisted to the database. In this example, the $product object's data doesn't exist in the database, so the entity manager executes an INSERT query, creating a new row in the product table.

Note

In fact, since Doctrine is aware of all your managed entities, when you call the flush() method, it calculates an overall changeset and executes the queries in the correct order. It utilizes cached prepared statement to slightly improve the performance. For example, if you persist a total of 100 Product objects and then subsequently call flush(), Doctrine will execute 100 INSERT queries using a single prepared statement object.

Whether creating or updating objects, the workflow is always the same. In the next section, you'll see how Doctrine is smart enough to automatically issue an UPDATE query if the entity already exists in the database.

Tip

Doctrine provides a library that allows you to programmatically load testing data into your project (i.e. "fixture data"). For information, see the "DoctrineFixturesBundle" documentation.

Fetching Objects from the Database

Fetching an object back out of the database is even easier. For example, suppose you've configured a route to display a specific Product based on its id value:

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public function showAction($productId)
{
    $product = $this->getDoctrine()
        ->getRepository('AppBundle:Product')
        ->find($productId);

    if (!$product) {
        throw $this->createNotFoundException(
            'No product found for id '.$productId
        );
    }

    // ... do something, like pass the $product object into a template
}

Tip

You can achieve the equivalent of this without writing any code by using the @ParamConverter shortcut. See the FrameworkExtraBundle documentation for more details.

When you query for a particular type of object, you always use what's known as its "repository". You can think of a repository as a PHP class whose only job is to help you fetch entities of a certain class. You can access the repository object for an entity class via:

$repository = $this->getDoctrine()
    ->getRepository('AppBundle:Product');

Note

The AppBundle:Product string is a shortcut you can use anywhere in Doctrine instead of the full class name of the entity (i.e. AppBundle\Entity\Product). As long as your entity lives under the Entity namespace of your bundle, this will work.

Once you have a repository object, you can access all sorts of helpful methods:

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// query for a single product by its primary key (usually "id")
$product = $repository->find($productId);

// dynamic method names to find a single product based on a column value
$product = $repository->findOneById($productId);
$product = $repository->findOneByName('Keyboard');

// dynamic method names to find a group of products based on a column value
$products = $repository->findByPrice(19.99);

// find *all* products
$products = $repository->findAll();

Note

Of course, you can also issue complex queries, which you'll learn more about in the Querying for Objects section.

You can also take advantage of the useful findBy and findOneBy methods to easily fetch objects based on multiple conditions:

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// query for a single product matching the given name and price
$product = $repository->findOneBy(
    array('name' => 'Keyboard', 'price' => 19.99)
);

// query for multiple products matching the given name, ordered by price
$products = $repository->findBy(
    array('name' => 'Keyboard'),
    array('price' => 'ASC')
);

Tip

When you render any page, you can see how many queries were made in the bottom right corner of the web debug toolbar.

../_images/doctrine_web_debug_toolbar.png

If you click the icon, the profiler will open, showing you the exact queries that were made.

The icon will turn yellow if there were more than 50 queries on the page. This could indicate that something is not correct.

Updating an Object

Once you've fetched an object from Doctrine, updating it is easy. Suppose you have a route that maps a product id to an update action in a controller:

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public function updateAction($productId)
{
    $em = $this->getDoctrine()->getManager();
    $product = $em->getRepository('AppBundle:Product')->find($productId);

    if (!$product) {
        throw $this->createNotFoundException(
            'No product found for id '.$productId
        );
    }

    $product->setName('New product name!');
    $em->flush();

    return $this->redirectToRoute('homepage');
}

Updating an object involves just three steps:

  1. fetching the object from Doctrine;
  2. modifying the object;
  3. calling flush() on the entity manager

Notice that calling $em->persist($product) isn't necessary. Recall that this method simply tells Doctrine to manage or "watch" the $product object. In this case, since you fetched the $product object from Doctrine, it's already managed.

Deleting an Object

Deleting an object is very similar, but requires a call to the remove() method of the entity manager:

$em->remove($product);
$em->flush();

As you might expect, the remove() method notifies Doctrine that you'd like to remove the given object from the database. The actual DELETE query, however, isn't actually executed until the flush() method is called.

Querying for Objects

You've already seen how the repository object allows you to run basic queries without any work:

$product = $repository->find($productId);
$product = $repository->findOneByName('Keyboard');

Of course, Doctrine also allows you to write more complex queries using the Doctrine Query Language (DQL). DQL is similar to SQL except that you should imagine that you're querying for one or more objects of an entity class (e.g. Product) instead of querying for rows on a table (e.g. product).

When querying in Doctrine, you have two main options: writing pure DQL queries or using Doctrine's Query Builder.

Querying for Objects with DQL

Imagine that you want to query for products that cost more than 19.99, ordered from least to most expensive. You can use DQL, Doctrine's native SQL-like language, to construct a query for this scenario:

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$em = $this->getDoctrine()->getManager();
$query = $em->createQuery(
    'SELECT p
    FROM AppBundle:Product p
    WHERE p.price > :price
    ORDER BY p.price ASC'
)->setParameter('price', 19.99);

$products = $query->getResult();

If you're comfortable with SQL, then DQL should feel very natural. The biggest difference is that you need to think in terms of selecting PHP objects, instead of rows in a database. For this reason, you select from the AppBundle:Product entity (an optional shortcut for the AppBundle\Entity\Product class) and then alias it as p.

Tip

Take note of the setParameter() method. When working with Doctrine, it's always a good idea to set any external values as "placeholders" (:price in the example above) as it prevents SQL injection attacks.

The getResult() method returns an array of results. To get only one result, you can use getOneOrNullResult():

$product = $query->setMaxResults(1)->getOneOrNullResult();

The DQL syntax is incredibly powerful, allowing you to easily join between entities (the topic of relations will be covered later), group, etc. For more information, see the official Doctrine Query Language documentation.

Querying for Objects Using Doctrine's Query Builder

Instead of writing a DQL string, you can use a helpful object called the QueryBuilder to build that string for you. This is useful when the actual query depends on dynamic conditions, as your code soon becomes hard to read with DQL as you start to concatenate strings:

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$repository = $this->getDoctrine()
    ->getRepository('AppBundle:Product');

// createQueryBuilder automatically selects FROM AppBundle:Product
// and aliases it to "p"
$query = $repository->createQueryBuilder('p')
    ->where('p.price > :price')
    ->setParameter('price', '19.99')
    ->orderBy('p.price', 'ASC')
    ->getQuery();

$products = $query->getResult();
// to get just one result:
// $product = $query->setMaxResults(1)->getOneOrNullResult();

The QueryBuilder object contains every method necessary to build your query. By calling the getQuery() method, the query builder returns a normal Query object, which can be used to get the result of the query.

For more information on Doctrine's Query Builder, consult Doctrine's Query Builder documentation.

Custom Repository Classes

In the previous sections, you began constructing and using more complex queries from inside a controller. In order to isolate, reuse and test these queries, it's a good practice to create a custom repository class for your entity. Methods containing your query logic can then be stored in this class.

To do this, add the repository class name to your entity's mapping definition:

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    // src/AppBundle/Entity/Product.php
    namespace AppBundle\Entity;
    
    use Doctrine\ORM\Mapping as ORM;
    
    /**
     * @ORM\Entity(repositoryClass="AppBundle\Entity\ProductRepository")
     */
    class Product
    {
        //...
    }
    
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    # src/AppBundle/Resources/config/doctrine/Product.orm.yml
    AppBundle\Entity\Product:
        type: entity
        repositoryClass: AppBundle\Entity\ProductRepository
        # ...
    
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    <!-- src/AppBundle/Resources/config/doctrine/Product.orm.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://doctrine-project.org/schemas/orm/doctrine-mapping.xsd">
    
        <entity
            name="AppBundle\Entity\Product"
            repository-class="AppBundle\Entity\ProductRepository">
    
            <!-- ... -->
        </entity>
    </doctrine-mapping>
    

Doctrine can generate empty repository classes for all the entities in your application via the same command used earlier to generate the missing getter and setter methods:

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$ php bin/console doctrine:generate:entities AppBundle

Tip

If you opt to create the repository classes yourself, they must extend Doctrine\ORM\EntityRepository.

Next, add a new method - findAllOrderedByName() - to the newly-generated ProductRepository class. This method will query for all the Product entities, ordered alphabetically by name.

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// src/AppBundle/Entity/ProductRepository.php
namespace AppBundle\Entity;

use Doctrine\ORM\EntityRepository;

class ProductRepository extends EntityRepository
{
    public function findAllOrderedByName()
    {
        return $this->getEntityManager()
            ->createQuery(
                'SELECT p FROM AppBundle:Product p ORDER BY p.name ASC'
            )
            ->getResult();
    }
}

Tip

The entity manager can be accessed via $this->getEntityManager() from inside the repository.

You can use this new method just like the default finder methods of the repository:

$em = $this->getDoctrine()->getManager();
$products = $em->getRepository('AppBundle:Product')
    ->findAllOrderedByName();

Note

When using a custom repository class, you still have access to the default finder methods such as find() and findAll().

Entity Relationships/Associations

Suppose that each product in your application belongs to exactly one category. In this case, you'll need a Category class, and a way to relate a Product object to a Category object.

Start by creating the Category entity. Since you know that you'll eventually need to persist category objects through Doctrine, you can let Doctrine create the class for you.

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$ php bin/console doctrine:generate:entity --no-interaction \
    --entity="AppBundle:Category" \
    --fields="name:string(255)"

This task generates the Category entity for you, with an id field, a name field and the associated getter and setter functions.

Relationship Mapping Metadata

In this example, each category can be associated with many products, while each product can be associated with only one category. This relationship can be summarized as: many products to one category (or equivalently, one category to many products).

From the perspective of the Product entity, this is a many-to-one relationship. From the perspective of the Category entity, this is a one-to-many relationship. This is important, because the relative nature of the relationship determines which mapping metadata to use. It also determines which class must hold a reference to the other class.

To relate the Product and Category entities, simply create a category property on the Product class, annotated as follows:

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    // src/AppBundle/Entity/Product.php
    
    // ...
    class Product
    {
        // ...
    
        /**
         * @ORM\ManyToOne(targetEntity="Category", inversedBy="products")
         * @ORM\JoinColumn(name="category_id", referencedColumnName="id")
         */
        private $category;
    }
    
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    # src/AppBundle/Resources/config/doctrine/Product.orm.yml
    AppBundle\Entity\Product:
        type: entity
        # ...
        manyToOne:
            category:
                targetEntity: Category
                inversedBy: products
                joinColumn:
                    name: category_id
                    referencedColumnName: id
    
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    <!-- src/AppBundle/Resources/config/doctrine/Product.orm.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://doctrine-project.org/schemas/orm/doctrine-mapping.xsd">
    
        <entity name="AppBundle\Entity\Product">
            <!-- ... -->
            <many-to-one
                field="category"
                target-entity="Category"
                inversed-by="products"
                join-column="category">
    
                <join-column name="category_id" referenced-column-name="id" />
            </many-to-one>
        </entity>
    </doctrine-mapping>
    

This many-to-one mapping is critical. It tells Doctrine to use the category_id column on the product table to relate each record in that table with a record in the category table.

Next, since a single Category object will relate to many Product objects, a products property can be added to the Category class to hold those associated objects.

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    // src/AppBundle/Entity/Category.php
    
    // ...
    use Doctrine\Common\Collections\ArrayCollection;
    
    class Category
    {
        // ...
    
        /**
         * @ORM\OneToMany(targetEntity="Product", mappedBy="category")
         */
        private $products;
    
        public function __construct()
        {
            $this->products = new ArrayCollection();
        }
    }
    
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    # src/AppBundle/Resources/config/doctrine/Category.orm.yml
    AppBundle\Entity\Category:
        type: entity
        # ...
        oneToMany:
            products:
                targetEntity: Product
                mappedBy: category
    # Don't forget to initialize the collection in
    # the __construct() method of the entity
    
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    <!-- src/AppBundle/Resources/config/doctrine/Category.orm.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://doctrine-project.org/schemas/orm/doctrine-mapping.xsd">
    
        <entity name="AppBundle\Entity\Category">
            <!-- ... -->
            <one-to-many
                field="products"
                target-entity="Product"
                mapped-by="category" />
    
            <!--
                don't forget to init the collection in
                the __construct() method of the entity
            -->
        </entity>
    </doctrine-mapping>
    

While the many-to-one mapping shown earlier was mandatory, this one-to-many mapping is optional. It is included here to help demonstrate Doctrine's range of relationship management capabailties. Plus, in the context of this application, it will likely be convenient for each Category object to automatically own a collection of its related Product objects.

Note

The code in the constructor is important. Rather than being instantiated as a traditional array, the $products property must be of a type that implements Doctrine's Collection interface. In this case, an ArrayCollection object is used. This object looks and acts almost exactly like an array, but has some added flexibility. If this makes you uncomfortable, don't worry. Just imagine that it's an array and you'll be in good shape.

Tip

The targetEntity value in the metadata used above can reference any entity with a valid namespace, not just entities defined in the same namespace. To relate to an entity defined in a different class or bundle, enter a full namespace as the targetEntity.

Now that you've added new properties to both the Product and Category classes, tell Doctrine to generate the missing getter and setter methods for you:

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$ php bin/console doctrine:generate:entities AppBundle

Ignore the Doctrine metadata for a moment. You now have two classes - Product and Category, with a natural many-to-one relationship. The Product class holds a single Category object, and the Category class holds a collection of Product objects. In other words, you've built your classes in a way that makes sense for your application. The fact that the data needs to be persisted to a database is always secondary.

Now, review the metadata above the Product entity's $category property. It tells Doctrine that the related class is Category, and that the id of the related category record should be stored in a category_id field on the product table.

In other words, the related Category object will be stored in the $category property, but behind the scenes, Doctrine will persist this relationship by storing the category's id in the category_id column of the product table.

../_images/doctrine_image_2.png

The metadata above the Category entity's $products property is less complicated. It simply tells Doctrine to look at the Product.category property to figure out how the relationship is mapped.

Before you continue, be sure to tell Doctrine to add the new category table, the new product.category_id column, and the new foreign key:

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$ php bin/console doctrine:schema:update --force

More Information on Associations

This section has been an introduction to one common type of entity relationship, the one-to-many relationship. For more advanced details and examples of how to use other types of relations (e.g. one-to-one, many-to-many), see Doctrine's Association Mapping Documentation.

Note

If you're using annotations, you'll need to prepend all annotations with ORM\ (e.g. ORM\OneToMany), which is not reflected in Doctrine's documentation. You'll also need to include the use Doctrine\ORM\Mapping as ORM; statement, which imports the ORM annotations prefix.

Configuration

Doctrine is highly configurable, though you probably won't ever need to worry about most of its options. To find out more about configuring Doctrine, see the Doctrine section of the config reference.

Lifecycle Callbacks

Sometimes, you need to perform an action right before or after an entity is inserted, updated, or deleted. These types of actions are known as "lifecycle" callbacks, as they're callback methods that you need to execute during different stages of the lifecycle of an entity (e.g. the entity is inserted, updated, deleted, etc).

If you're using annotations for your metadata, start by enabling the lifecycle callbacks. This is not necessary if you're using YAML or XML for your mapping.

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/**
 * @ORM\Entity()
 * @ORM\HasLifecycleCallbacks()
 */
class Product
{
    // ...
}

Now, you can tell Doctrine to execute a method on any of the available lifecycle events. For example, suppose you want to set a createdAt date column to the current date, only when the entity is first persisted (i.e. inserted):

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    // src/AppBundle/Entity/Product.php
    
    /**
     * @ORM\PrePersist
     */
    public function setCreatedAtValue()
    {
        $this->createdAt = new \DateTime();
    }
    
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    # src/AppBundle/Resources/config/doctrine/Product.orm.yml
    AppBundle\Entity\Product:
        type: entity
        # ...
        lifecycleCallbacks:
            prePersist: [setCreatedAtValue]
    
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    <!-- src/AppBundle/Resources/config/doctrine/Product.orm.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://doctrine-project.org/schemas/orm/doctrine-mapping.xsd">
    
        <entity name="AppBundle\Entity\Product">
            <!-- ... -->
            <lifecycle-callbacks>
                <lifecycle-callback type="prePersist" method="setCreatedAtValue" />
            </lifecycle-callbacks>
        </entity>
    </doctrine-mapping>
    

Note

The above example assumes that you've created and mapped a createdAt property (not shown here).

Now, right before the entity is first persisted, Doctrine will automatically call this method and the createdAt field will be set to the current date.

There are several other lifecycle events that you can hook into. For more information on other lifecycle events and lifecycle callbacks in general, see Doctrine's Lifecycle Events documentation.

Notice that the setCreatedAtValue() method receives no arguments. This is always the case for lifecycle callbacks and is intentional: lifecycle callbacks should be simple methods that are concerned with internally transforming data in the entity (e.g. setting a created/updated field, generating a slug value).

If you need to do some heavier lifting - like performing logging or sending an email - you should register an external class as an event listener or subscriber and give it access to whatever resources you need. For more information, see How to Register Event Listeners and Subscribers.

Doctrine Field Types Reference

Doctrine comes with numerous field types available. Each of these maps a PHP data type to a specific column type in whatever database you're using. For each field type, the Column can be configured further, setting the length, nullable behavior, name and other options. To see a list of all available types and more information, see Doctrine's Mapping Types documentation.

Summary

With Doctrine, you can focus on your objects and how they're used in your application and worry about database persistence second. This is because Doctrine allows you to use any PHP object to hold your data and relies on mapping metadata information to map an object's data to a particular database table.

And even though Doctrine revolves around a simple concept, it's incredibly powerful, allowing you to create complex queries and subscribe to events that allow you to take different actions as objects go through their persistence lifecycle.

Learn more

For more information about Doctrine, see the Doctrine section of the cookbook. Some useful articles might be:

This work, including the code samples, is licensed under a Creative Commons BY-SA 3.0 license.