How is a pivot table created by Laravel?

Question

In Laravel 4, when working with many-to-many relationships as described in the 4.2 docs, how can I actually get Laravel to create the pivot table for me?

Do I need to add something in my migrations for the two models that are involved? Do I need to manually create a migration for the pivot table? Or how does Laravel know to create the pivot table?

All I've done so far is add the belongsToMany information to the two respective models, i.e.

class User extends Eloquent 
{
    public function roles()
    {
         return $this->belongsToMany('Role');
     }
 }

However, that does not trigger creation of the pivot table. What step am I missing?

Solution 1

It appears as though the pivot table does need to be created manually (i.e. Laravel does not do this automatically). Here's how to do it:

1.) Create a new migration, using singular table names in alphabetical order (default):

php artisan make:migration create_alpha_beta_table --create --table=alpha_beta

2.) Inside the newly created migration, change the up function to:

public function up()
{
    Schema::create('alpha_beta', function(Blueprint $table)
    {
        $table->increments('id');
        $table->integer('alpha_id');
        $table->integer('beta_id');
    });
}

3.) Add the foreign key constraints, if desired. (I haven't gotten to that bit, yet).

---

Now to seed, say, the alpha table, using keys from beta, you can do the following in your AlphaTableSeeder:

public function run()
{
    DB::table('alpha')->delete();

    Alpha::create( array( 
        'all'           =>  'all',
        'your'          =>  'your',
        'stuff'         =>  'stuff',
    ) )->beta()->attach( $idOfYourBeta );
}

Solution 2

I use Jeffrey Way's Laravel-4-Generators or Laravel-5-Generators-Extended.

then you can just use this artisan command:

php artisan generate:pivot table_one table_two

Solution 3

To expand on Ben's answer (I tried to edit it but reviewers said it added too much):

To add the foreign key constraints, make sure if alpha id is unsigned, alpha_id is also unsigned in the pivot table. This migration would run after (2) in Ben's answer since it alters the table created then.

public function up()
{
    Schema::table('alpha_beta', function(Blueprint $table)
    {
        $table->foreign('alpha_id')->references('id')->on('alpha');
        $table->foreign('beta_id')->references('id')->on('beta');
    });
}

Solution 4

For Many to Many relationships you can create the Migration file of the Database manually like this:

use Illuminate\Database\Migrations\Migration;
use Illuminate\Database\Schema\Blueprint;

class CreateAccountTagTable extends Migration
{

    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::create('account_tag', function (Blueprint $table) {
            // $table->timestamps(); // not required
            // $table->softDeletes(); // not required

            $table->integer('account_id')->unsigned();
            $table->foreign('account_id')->references('id')->on('accounts');

            $table->integer('tag_id')->unsigned()->nullable();
            $table->foreign('tag_id')->references('id')->on('tags');
        });
    }

    /**
     * Reverse the migrations.
     *
     * @return void
     */
    public function down()
    {
        Schema::drop('account_tag');
    }
}

Note: in case you have timestamps on the pivot table you must set withTimestamps on the relationship of both ends like this:

return $this->belongsToMany(\Mega\Modules\Account\Models\Tag::class)->withTimestamps();

.

return $this->belongsToMany(\Mega\Modules\Account\Models\Account::class)->withTimestamps();

Solution 5

1. Create new migration:

php artisan make:migration create_alpha_beta_table --create=alpha_beta

2. Inside the newly created migration:

public function up() {
    Schema::create('alpha_beta', function(Blueprint $table) {
            $table->increments('id');
            $table->unsignedBigInteger('alpha_id');
            $table->unsignedBigInteger('beta_id');
            // foreign keys
            $table->foreign('alpha_id')->references('id')->on('alphas');
            $table->foreign('beta_id')->references('id')->on('betas');
     });
}

View more solutions

Comments

[sersun]

If you are getting 'call to undefined method..." when your seed tries to run that {model}()->attach(/... method, remember to created a model for both tablese, with a belongstomany in one of them. Eg, for this example: In models/Alpha.php you would include: public function beta() { return $this->belongsToMany('Beta'); }

[dan-klasson]

This creates the foreign key constraints as well.

[Adamski]

I think step 1 should be: php artisan migrate:make create_alpha_beta_table --create=alpha_beta

[Afzal N]

Whoever downvoted on a 1.5 year old answer. Next time, comment for correction.

[Jon]

For Laravel-5-Generators-Extended, the command is make:migration:pivot and no longer generate:pivot (as it was in Laravel-4-Generators).

[Miguel Stevens]

is that first id field necessary?

[Khan Shahrukh]

would you like to add an onDelete('cascade'); ?

[Tharaka Dilshan]

for intermediate pivot tables, there should't be a primary key.

[okdewit]

Drop the id, add foreign keys, and in most cases you also want a unique index covering both FKs.

[Adam]

@TharakaDilshan I agree, no AI primary key is needed. However, the touple [alpha_id,beta_id] should be the primary key, or at least indexed! Otherwise you query spped will slow downa lot

[Salman Malik]

$table->foreignId('alpha_id')->constrained(); or $table->foreignId('alpha_id') and vice versa can be a better approach now.