Laravel: Unique foreign key per another foreign key (user_id)

I have a UserCategoryFollows table which has a user_id related to Users and a category_id related to Categories.

Users can follow any amount of Categories, but I don't want to insert multiple rows for the same category_id and user_id.

For example, I don't want this in my database:

user_id     category_id
1           2
2           1
2           3
1           4
2           1   <---- Duplicate
1           2   <---- Duplicate

Is this something I can validate inside the Model or is this validation done via controllers?

I'm currently seeding:

public function run()
    {

        $catCount = App\Category::count();
        $faker = \Faker\Factory::create();
        $follows = [];

        for ($i = 0; $i < 100; $i++) {
            $user_id = App\User::all()->random()->id;
            $category_id = $faker->numberBetween(1, $catCount);

            $follow = [
                'user_id' => $user_id,
                'category_id' => $category_id
            ];


                array_push($follows, $follow);



        }



        foreach ($follows as $follow) {
            App\UserCategoryFollow::create($follow);
        }

    }

I could alter my array to pluck out duplicates, but I think it would be better to handle on the model if possible.

Initially, you want to add this line to your migration file (this step is optional but it is better to implement it to ensure data integrity)

$table->unique(['user_id', 'category_id']);

Secondly, use firstOrCreate based on your user_id and category id to automatically avoid inserting non-unique values

    for ($i = 0; $i < 100; $i++) {
        $user_id = App\User::all()->random()->id;
        $category_id = $faker->numberBetween(1, $catCount);
        App\UserCategoryFollow::firstOrCreate( ['user_id' => $user_id,'category_id' => $category_id]);
    }