How to Handle Many-to-Many Relationships with Extra Fields in Doctrine 2?

Doctrine 2 and Many-to-many Link Table with Extra Field: Clarified

Clarifying the Query

In the original question, the user sought guidance on creating a many-to-many relationship within a link table that contained an additional field (stock amount). The challenge arose when accessing the stock amount value using Doctrine and generating the database table structure.

Addressing the Issue

The issue stemmed from the assumption that a many-to-many relationship with additional values could be treated as such. However, a many-to-many relationship with additional values becomes a new entity with an identifier and values.

Solution

The solution involved creating a separate entity called Stock with the following columns:

• Amount (to store the stock value)
• Relationships to both Product and Store entities

This allowed the system to model the many-to-many relationship accurately, providing access to the stock amount value using Doctrine.

Updated Entities

Below are the adjusted entity definitions:

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\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;
}

Database Structure

This change resulted in the database structure shown below:

CREATE TABLE product (
  id INT NOT NULL,
  product_name VARCHAR(50) NOT NULL,
  PRIMARY KEY (id)
);

CREATE TABLE store (
  id INT NOT NULL,
  store_name VARCHAR(50) NOT NULL,
  PRIMARY KEY (id)
);

CREATE TABLE stock (
  amount INT NOT NULL,
  store_id INT NOT NULL,
  product_id INT NOT NULL,
  PRIMARY KEY (store_id, product_id),
  FOREIGN KEY (store_id) REFERENCES store (id),
  FOREIGN KEY (product_id) REFERENCES product (id)
);

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