Pivot table factory seeding

if you have a dedicated model for assigned_users (e.g. UserPost), use this approach:

$factory->define(App\UserPost::class, function (Faker $faker) {  
    return [  
        'user_id' => factory(App\User::class)->create()->id,  
        'post_id' => factory(App\Post::class)->create()->id,
    ];
});  

if you don't, use a DB table insert:

DB::table('assigned_users')->insert(
    [
        'user_id' => factory(App\User::class)->create()->id,  
        'post_id' => factory(App\Post::class)->create()->id,
    ]
);

and finally, if you want to use existing users/posts, use a callback

DB::table('assigned_users')->insert(
    [
        'user_id' => function () {  
            return App\User::all()->random()->id;  
        },
        'post_id' => function () {  
            return App\Post::all()->random()->id;  
        },
    ]
);

that should yield some multiple assigned users by chance, or better yet amend the callback as you wish to randomize only couple of them

You should set up the relationships first within the model, then reference the relationships in the seeder.

For example if you have a many-to-many relationship between USER and POST, and you are creating posts and users individually, you could just do something like:

$post_1 = Post::create(['title'=>'foo']);
$user_1 = User::create(['first_name'=>'Paul']);

$user_1->posts()->attach($post_1->id);

// or alternatively

$post_1->users()->attach($user_1->id);

On the other hand, if you're using factories, you could do something like this:

$users = factory(User::class, 10)->create()->each(function($user) {
      $user->posts()->attach(factory(Post::class)->create()->id);
});

I don't know fam, the callback is no longer working in Laravel 8x for me. But it works directly like this: 'user_id' => App\User::all()->random()->id,