How to Model Many-to-Many Relationships with Additional Values in Doctrine 2 Using a Link Table?

Doctrine 2 and Many-to-many Link Table with an Additional Field

Understanding Many-to-Many Relationships with Additional Values

In a relational database model, a many-to-many relationship represents a scenario where multiple rows from one table can be associated with multiple rows from another. However, when additional values are introduced into this relationship, it transforms into a new entity. This entity possesses an identifier (the two relations to the connected entities) and additional data.

Modeling Many-to-Many Relationships with Additional Values in Doctrine 2

To effectively model many-to-many relationships with additional values in Doctrine 2, consider creating a separate table to represent the relationship. This table, commonly referred to as a "link table," will contain the necessary columns to establish relationships with both parent tables, as well as any additional attribute(s) associated with the relationship.

Mapping the Link Table Entity in Doctrine 2

In the context of Doctrine 2, you can map this link table as a new entity. Let's take an example scenario involving products and stores:

Product Entity:

<code class="php">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;
}</code>

Store Entity:

<code class="php">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;
}</code>

Stock Entity:

<code class="php">namespace Entity;

use Doctrine\ORM\Mapping as ORM;

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

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

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

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