How to Generate Entities from an Existing Database

When starting work on a brand new project that uses a database, two different situations comes naturally. In most cases, the database model is designed and built from scratch. Sometimes, however, you'll start with an existing and probably unchangeable database model. Fortunately, Doctrine comes with a bunch of tools to help generate model classes from your existing database.

This tutorial assumes you're using a simple blog application with the following two tables: blog_post and blog_comment. A comment record is linked to a post record thanks to a foreign key constraint.

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CREATE TABLE `blog_post` (
  `id` bigint(20) NOT NULL AUTO_INCREMENT,
  `title` varchar(100) COLLATE utf8_unicode_ci NOT NULL,
  `content` longtext COLLATE utf8_unicode_ci NOT NULL,
  `created_at` datetime NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;

CREATE TABLE `blog_comment` (
  `id` bigint(20) NOT NULL AUTO_INCREMENT,
  `post_id` bigint(20) NOT NULL,
  `author` varchar(20) COLLATE utf8_unicode_ci NOT NULL,
  `content` longtext COLLATE utf8_unicode_ci NOT NULL,
  `created_at` datetime NOT NULL,
  PRIMARY KEY (`id`),
  KEY `blog_comment_post_id_idx` (`post_id`),
  CONSTRAINT `blog_post_id` FOREIGN KEY (`post_id`) REFERENCES `blog_post` (`id`) ON DELETE CASCADE
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;

Before diving into the recipe, be sure your database connection parameters are correctly setup in the app/config/parameters.yml file (or wherever your database configuration is kept) and that you have initialized a bundle that will host your future entity class. In this tutorial it's assumed that an AcmeBlogBundle exists and is located under the src/Acme/BlogBundle folder.

The first step towards building entity classes from an existing database is to ask Doctrine to introspect the database and generate the corresponding metadata files. Metadata files describe the entity class to generate based on table fields.

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$ php app/console doctrine:mapping:import --force AcmeBlogBundle xml

This command line tool asks Doctrine to introspect the database and generate the XML metadata files under the src/Acme/BlogBundle/Resources/config/doctrine folder of your bundle. This generates two files: BlogPost.orm.xml and BlogComment.orm.xml.

The generated BlogPost.orm.xml metadata file looks as follows:

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<?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="Acme\BlogBundle\Entity\BlogPost" table="blog_post">
    <id name="id" type="bigint" column="id">
      <generator strategy="IDENTITY"/>
    </id>
    <field name="title" type="string" column="title" length="100" nullable="false"/>
    <field name="content" type="text" column="content" nullable="false"/>
    <field name="createdAt" type="datetime" column="created_at" nullable="false"/>
  </entity>
</doctrine-mapping>

Once the metadata files are generated, you can ask Doctrine to build related entity classes by executing the following command.

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// generates entity classes with annotation mappings
$ php app/console doctrine:mapping:convert annotation ./src

For example, the newly created BlogComment entity class looks as follow:

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// src/Acme/BlogBundle/Entity/BlogComment.php
namespace Acme\BlogBundle\Entity;

use Doctrine\ORM\Mapping as ORM;

/**
 * Acme\BlogBundle\Entity\BlogComment
 *
 * @ORM\Table(name="blog_comment")
 * @ORM\Entity
 */
class BlogComment
{
    /**
     * @var integer $id
     *
     * @ORM\Column(name="id", type="bigint")
     * @ORM\Id
     * @ORM\GeneratedValue(strategy="IDENTITY")
     */
    private $id;

    /**
     * @var string $author
     *
     * @ORM\Column(name="author", type="string", length=100, nullable=false)
     */
    private $author;

    /**
     * @var text $content
     *
     * @ORM\Column(name="content", type="text", nullable=false)
     */
    private $content;

    /**
     * @var datetime $createdAt
     *
     * @ORM\Column(name="created_at", type="datetime", nullable=false)
     */
    private $createdAt;

    /**
     * @var BlogPost
     *
     * @ORM\ManyToOne(targetEntity="BlogPost")
     * @ORM\JoinColumn(name="post_id", referencedColumnName="id")
     */
    private $post;
}

As you can see, Doctrine converts all table fields to pure private and annotated class properties. The most impressive thing is that it also discovered the relationship with the BlogPost entity class based on the foreign key constraint. Consequently, you can find a private $post property mapped with a BlogPost entity in the BlogComment entity class.

The generated entities are now ready to be used. Have fun!