Relation between 3 entities

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Relation between 3 entities

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I have the following tables:

+----------+  +----------------------+ +------------+
| Produtos |  | ProdutosVsCategorias | | Categorias |
+----------+  +----------------------+ +------------+
- ID          - ID                     - ID
- TITULO      - ID_PRODUTO             - TITULO
              - ID_CATEGORIA

The Produtos table contains all my products

The ProdutosVsCategorias table has a relation to the Produtos and Categorias table.

The relationship between the Produtos and ProdutosVsCategorias tables occurs through the ID and ID_PRODUTO fields respectively and is OneToMany.

The relationship between the ProdutosVsCategorias and Categorias tables occurs through the ID_CATEGORIA and ID fields respectively and is ManyToOne.

For each table, I created an entity, but I do not know how to do the relationship between entities in Symfony using Doctrine.

When instantiating the Produto entity, I need to know which categories are associated with the product.

When instantiating a category, I also need to know which products are associated with the category.

How to make the relationship between entities using the above example?

symfony-2 doctrine

asked by anonymous 28.08.2015 / 13:03

1 answer

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score 0 · Accepted Answer

Depends on the case. You can create a many-to-many relationship between the Produto and Categoria entities, or two many-to-one relationships, and Produto , and another between ProdutoVsCategoria and ProdutoVsCategoria . The difference is that when you make the relationship using two many-to-one relationships, you can customize the intermediary entity (more attributes, for example).

This explanation is found in the Doctrine documentation:

Why are many-to-many associations less common? Because you frequently want to associate additional attributes with an association, in which case you introduce an association class. Consequently, the direct many-to-many association disappears and is replaced by one-to-many / many-to-one associations among the 3 participating classes.

link

But I'll explain how to do it using two entities.

First, create the classes for the Categoria and Categorias tables.

Class Produtos :

<?php

namespace AppBundle\Entity;

use Doctrine\ORM\Mapping as ORM;

/**
 * @ORM\Entity;
 * @ORM\Table(name="Produtos")
 */
class Produto
{
    /**
     * @ORM\Column(type="integer")
     * @ORM\Id
     * @ORM\GeneratedValue(strategy="AUTO")
     */
    private $id;

    /**
     * @ORM\ManyToMany(targetEntity="Categoria", mappedBy="produtos")
     */
    private $categorias;

    /**
     * @ORM\Column(type="string")
     */
    private $titulo;
}

Class Produto :

<?php

namespace AppBundle\Entity;

use Doctrine\ORM\Mapping as ORM;

/**
 * @ORM\Entity;
 * @ORM\Table(name="Categorias")
 */
class Categoria
{
    /**
     * @ORM\Column(type="integer")
     * @ORM\Id
     * @ORM\GeneratedValue(strategy="AUTO")
     */
    private $id;

    /**
     * @ORM\ManyToMany(targetEntity="Produto", inversedBy="categorias")
     * @ORM\JoinTable(name="ProdutosVsCategorias")
     */
    private $produtos;

    /**
     * @ORM\Column(type="string")
     */
    private $titulo;
}

(do not forget to match the namespaces to your project's namespaces )

After that, just use the Categoria command to create the table schema in the database configured in your php app/console doctrine:schema:create file.