I'm new to Laravel and I'm looking for a good way to seed a pivot table using factories. I don't want to use plain seeders. I'll show you the case:

I have three tables (users, skills, and user_skill).

users                user_skill                 skills
+----------------+   +----------------------+   +-----------------+
| id  | name     |   | user_id | section_id |   | id  | skills    |
+----------------+   +----------------------+   +-----------------+
| 1   | Alex     |   |         |            |   | 1   | draw      |
|----------------|   |----------------------|   |-----------------|
| 2   | Lucy     |   |         |            |   | 2   | program   |
|----------------|   |----------------------|   |-----------------|
| 3   | Max      |   |         |            |   | 3   | social    |
|----------------|   |----------------------|   +-----------------+
| 4   | Sam      |   |         |            |
+----------------+   +----------------------+

Is there a good way to take real Id's of the Users table and real Id's of Skills table to seed the pivot table? I want to do it randomly, but I don't want random numbers that doesn't match to any id. I want the Id to match with the users and skills.

I don't know how to start, and I'm looking for a good example. Maybe something like this?

$factory->defineAs(App\User::class, 'userSkills', function ($faker) {
    return [
        'user_id' => ..?
        'skills_id' => ..?
    ];
});

I do not think that this is the best approach but it works for me.

$factory->define(App\UserSkill::class, function (Faker\Generator $faker) {
    return [
        'user_id' => factory(App\User::class)->create()->id,
        'skill_id' => factory(App\Skill::class)->create()->id,
    ];
});

If you do not want to create a model just for the pivot table, you can insert it manually.

DB::table('user_skill')->insert(
    [
        'user_id' => factory(App\User::class)->create()->id,
        'skill_id' => factory(App\Skill::class)->create()->id,
    ]
);

Or, with random existing values.

DB::table('user_skill')->insert(
    [
        'user_id' => User::select('id')->orderByRaw("RAND()")->first()->id,
        'skill_id' => Skill::select('id')->orderByRaw("RAND()")->first()->id,
    ]
);

I hade a similar problem and a resolved this way on Laravel testing.

Don't need create a new userSkills Model:

Version Laravel 5.7

Database

users                user_skill                               skills
+----------------+   +------------------------------------+   +-----------------+
| id  | name     |   | user_id | section_id | state_skill |   | id  | skills    |
+----------------+   +------------------------------------+   +-----------------+
| 1   | Alex     |   |         |            |             |   | 1   | draw      |
|----------------|   |----------------------|-------------|   |-----------------|
| 2   | Lucy     |   |         |            |             |   | 2   | program   |
|----------------|   |----------------------|-------------|   |-----------------|
| 3   | Max      |   |         |            |             |   | 3   | social    |
|----------------|   |----------------------|-------------|   +-----------------+
| 4   | Sam      |   |         |            |             |
+----------------+   +----------------------+-------------+

User.php

<?php

namespace App;

use Illuminate\Notifications\Notifiable;
use Illuminate\Contracts\Auth\MustVerifyEmail;
use Illuminate\Foundation\Auth\User as Authenticatable;

use Illuminate\Database\Eloquent\SoftDeletes;

class User extends Authenticatable
{
    use Notifiable;
    use SoftDeletes;

    public function skills()
    {
        return $this->belongsToMany('App\Skill')
                ->withTimestamps()
                ->withPivot('state_skill');
    }
}

DataBaseTest.php

<?php

namespace Tests\Unit;

use Tests\TestCase;
use Illuminate\Foundation\Testing\WithFaker;
use Illuminate\Foundation\Testing\RefreshDatabase;
use Illuminate\Support\Facades\Schema;

class DataBaseTest extends TestCase
{

    /**
     * @test
     */    
    public function test_create_user_skill()
    {
       // Create DataBase
       $users = factory(\App\User::class, 1)
           ->create()
           ->each(function ($user) {

                // Create Models Support
                $skill = factory(\App\Skill::class)->create();

                // Create Pivot with Parameters
                $user->skills()->attach($skill->id,[
                    'state_skill' => 'ok'
                ]);

            });

        // Testing
        // ...
        $this->assertTrue(true);
    }
}