Laravel On Delete Set Null

Laravel is a popular PHP web application framework. One of its features is the ability to define relationships between database tables. When tables are related, it is important to manage what happens to related records when a record is deleted. One option is to use "on delete set null", which means that when a record is deleted, any related records will have their foreign key column set to null.

Defining Relationships

Before we can use "on delete set null", we need to define relationships between our tables. In this example, we have a "users" table and a "posts" table. Each post belongs to a user, so we can define a "belongsTo" relationship in our Post model:

class Post extends Model
{
    public function user()
    {
        return $this->belongsTo(User::class);
    }
}

This tells Laravel that each post belongs to a user, and the user record can be accessed via the "user" method.

Using On Delete Set Null

Now that we have our relationship defined, we can use "on delete set null" to manage what happens when a user is deleted. To do this, we need to modify our "user_id" foreign key column in the "posts" table:

Schema::table('posts', function (Blueprint $table) {
    $table->unsignedBigInteger('user_id')->nullable()->change();
    $table->foreign('user_id')->references('id')->on('users')->onDelete('set null');
});

The "nullable" method call makes the foreign key column nullable, so that it can be set to null when a user is deleted. The "onDelete" method call sets the "on delete" behavior to "set null".

Conclusion

Using "on delete set null" is a useful way to manage what happens to related records when a record is deleted. Laravel makes it easy to define relationships and manage these behaviors.