How to Implement a Many-to-Many Relationship with Extra Fields in Doctrine 2?

Many-to-many link table with additional field in Doctrine 2

Entity Setup

Doctrine 2 interprets a many-to-many relationship as an entity when it contains additional properties, becoming a separate entity with its own unique identifier. This is essential for tracking values associated with each relationship.

To implement this in your database, consider the following entity structure:

Product:

namespace Entity;

use Doctrine\ORM\Mapping as ORM;

/**
 * @ORM\Table(name="product")
 * @ORM\Entity()
 */
class Product
{
    /**
     * @ORM\Id()
     * @ORM\Column(type="integer")
     */
    protected $id;

    /**
     * @ORM\Column(name="product_name", type="string", length=50, nullable=false)
     */
    protected $name;

    /**
     * @ORM\OneToMany(targetEntity="Entity\Stock", mappedBy="product")
     */
    protected $stockProducts;
}

Store:

namespace Entity;

use Doctrine\ORM\Mapping as ORM;

/**
 * @ORM\Table(name="store")
 * @ORM\Entity()
 */
class Store
{
    /**
     * @ORM\Id()
     * @ORM\Column(type="integer")
     */
    protected $id;

    /**
     * @ORM\Column(name="store_name", type="string", length=50, nullable=false)
     */
    protected $name;

    /**
     * @ORM\OneToMany(targetEntity="Entity\Stock", mappedBy="store")
     */
    protected $stockProducts;
}

Stock:

namespace Entity;

use Doctrine\ORM\Mapping as ORM;

/**
 * @ORM\Table(name="stock")
 * @ORM\Entity()
 */
class Stock
{
    /**
     * @ORM\Column(type="integer")
     */
    protected $amount;

    /**
     * @ORM\ManyToOne(targetEntity="Entity\Store", inversedBy="stockProducts")
     * @ORM\JoinColumn(name="store_id", referencedColumnName="id", nullable=false)
     */
    protected $store;

    /**
     * @ORM\ManyToOne(targetEntity="Entity\Product", inversedBy="stockProducts")
     * @ORM\JoinColumn(name="product_id", referencedColumnName="id", nullable=false)
     */
    protected $product;
}

This setup establishes three entities: Product, Store, and Stock. The Stock entity contains the amount field as an additional property, making it a Many-To-Many relationship with values.

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