Doctrine2: How Do I Implement On Delete Cascade for seamless database maintenance?

Doctrine2: Understanding On Delete Cascade

For seamless database maintenance, it's often necessary to automatically delete child records when the corresponding parent record is deleted. Doctrine2 supports this functionality through "On Delete Cascade," a feature that ensures child records are removed when their parent is.

Example Entities

Consider the following entities:

<code class="php">class Child {
    /** @ORM\ManyToOne(targetEntity="Father", cascade={"remove"}) */
    private $father;
}

class Father {
    /** @ORM\Id @ORM\GeneratedValue */
    private $id;
}</code>

The Problem: Missing Database Cascade

While the code establishes a relationship between Child and Father with a "remove" cascade, the database lacks the "On Delete Cascade" constraint.

Solution: Database-Level Cascade

To implement true On Delete Cascade, add onDelete="CASCADE" to the child's join column:

<code class="php">/** @ORM\JoinColumn(name="father_id", referencedColumnName="id", onDelete="CASCADE") */</code>

This specifies that when a row is deleted from the Father table, all matching rows in the Child table will be automatically deleted.

Caution: Understand Cascades

It's important to note the distinction between ORM-level and database-level cascades. ORM-level cascades operate within Doctrine's UnitOfWork and do not affect the database structure, while database-level cascades create physical constraints in the database. In the current example, the cascade={"remove"} is an ORM-level cascade that will trigger a recursive deletion in the UnitOfWork, but it won't result in the desired database behavior.

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