laravel migration best way to add foreign key

问题:

Simple question: I'm new to Laravel. I have this migration file:

Schema::create('lists', function(Blueprint $table) {
    $table->increments('id'); 
    $table->string('title', 255);
    $table->integer('user_id')->unsigned(); 
    $table->foreign('user_id')->references('id')->on('users'); 
    $table->timestamps();
});

I want to update it to add onDelete('cascade').

What's the best way to do this?

回答1:

Firstly you have to make your user_id field an index:

$table->index('user_id');

After that you can create a foreign key with an action on cascade:

$table->foreign('user_id')->references('id')->on('users')->onDelete('cascade');

If you want to do that with a new migration, you have to remove the index and foreign key firstly and do everything from scratch.

On down() function you have to do this and then on up() do what I've wrote above:

$table->dropForeign('lists_user_id_foreign');
$table->dropIndex('lists_user_id_index');
$table->dropColumn('user_id');

回答2:

You should create a new migration file let's say 'add_user_foreign_key.php'

public function up()
{
    Schema::table('lists', function(Blueprint $table)
    {
         $table->foreign('user_id')->references('id')->on('users')->onDelete('cascade');
    });
}

/**
 * Reverse the migrations.
 *
 * @return void
 */
public function down()
{
    Schema::table('lists', function(Blueprint $table)
    {
    $table->dropForeign('user_id'); //
    });
}  

The run

 php artisan migrate

回答3:

$table->integer('user_id')->unsigned();
$table->foreign('user_id')->references('id')->on('users');

In this example, we are stating that the user_id column references the id column on the users table. Make sure to create the foreign key column first! The user_id column is declared unsigned because it cannot have negative value.

You may also specify options for the "on delete" and "on update" actions of the constraint:

$table->foreign('user_id')
      ->references('id')->on('users')
      ->onDelete('cascade');

To drop a foreign key, you may use the dropForeign method. A similar naming convention is used for foreign keys as is used for other indexes:

$table->dropForeign('posts_user_id_foreign');

If you are fairly new to Laravel and Eloquent, try out the Laravel From Scratch series available on laracasts. It is a great guide for beginners.

回答4:

If you want to add onDelete('cascade'), just drop the indexes and create them again:

public function up()
{
    Schema::table('lists', function($table)
    {
        $table->dropForeign('lists_user_id_foreign');

        $table->foreign('user_id')->references('id')->on('users')->onDelete('cascade');
    });
}

public function down()
{
    Schema::table('lists', function($table)
    {
        $table->dropForeign('lists_user_id_foreign');

        $table->foreign('user_id')->references('id')->on('users');
    });
}