How to Generate Entities from an Existing Database

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.

Note

As the Doctrine tools documentation says, reverse engineering is a one-time process to get started on a project. Doctrine is able to convert approximately 70-80% of the necessary mapping information based on fields, indexes and foreign key constraints. Doctrine can't discover inverse associations, inheritance types, entities with foreign keys as primary keys or semantical operations on associations such as cascade or lifecycle events. Some additional work on the generated entities will be necessary afterwards to design each to fit your domain model specificities.

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.

Tip

It's also possible to generate the metadata files in YAML format by changing the last argument to yml.

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 two commands.

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$ php app/console doctrine:mapping:convert annotation ./src
$ php app/console doctrine:generate:entities AcmeBlogBundle

The first command generates entity classes with annotation mappings. But if you want to use YAML or XML mapping instead of annotations, you should execute the second command only.

Tip

If you want to use annotations, you can safely delete the XML (or YAML) files after running these two commands.

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.

Note

If you want to have a one-to-many relationship, you will need to add it manually into the entity or to the generated XML or YAML files. Add a section on the specific entities for one-to-many defining the inversedBy and the mappedBy pieces.

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

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