Get ids array from related laravel model which is having belongsToMany relationship

Title: Efficiently Retrieving User IDs from BelongsToMany Relationship in Laravel

In the world of Laravel applications, relationships between models are essential to achieve seamless data handling and improve scalability. One such relationship is belongsToMany, which allows a model to have multiple instances of another related model. In this blog post, we address retrieving user IDs from a belongsToMany relationship when a role has many users associated with it.

Problem Statement

You are working on an application where roles belong to multiple users, but you need only the list of user_ids (not the entire User object) for each role. How can you achieve this efficiently and effectively in Laravel? Let's first review the code used to establish the relationship between Role and User models.

Code Example

Class Role {
     public $fillable = ["name"];

     public function users()
     {
          return $this->belongsToMany('App/Models/User')->select(['user_id']);
     }
}

In the above code, we define the relationship between Role and User models using belongsToMany. Additionally, you can see that we've used the select method to only retrieve the "user_id" column from the Users table when retrieving users related to a role.

However, this approach returns all user data as an array of objects:

 [ 
   {
     "name": "Role1",
     "users" : [
        {
           user_id : 1
        },
        {
           user_id : 2
        },

        {
           user_id : 3
        }
   },
   {
     "name": "Role2",
     "users" : [
        {
           user_id : 1
        },
        {
           user_id : 2
        },

        {
           user_id : 3
        }
     ]
   }
 ]

Solution: Retrieve User IDs Only

To achieve this, we need to use Laravel's Eloquent query builder and apply a few modifications. Firstly, let's modify the relationship definition in the Role model slightly:

Class Role {
     public $fillable = ["name"];

     public function users()
     {
          return $this->belongsToMany('App/Models/User')->select(['user_id']);
     }
}

Next, when retrieving roles and their associated users using the with method:

Role::with("users")->get();

Laravel will automatically create a new collection of Roles containing the original Role data (name) prefixed with a role object and an additional property called 'users' which is another nested array of User objects. In this case, we don't need these User objects; we only want their IDs for each role. To retrieve user IDs, you can use Laravel's Collection feature to iterate over the users property of each role and generate an array containing only user_ids:

Collection::make(Role::with("users")->get())->map(function($role) {
    return $role->users->pluck('user_id');
})->all();

This code snippet will create a new Collection object from the roles and iterate through each role, extracting user IDs from their users property. Finally, the last line converts this new collection back into an array. You can also use Laravel's pluck method to concatenate all user_ids from multiple roles:

Role::with("users")->get()->pluck('users', 'role_id')->map(function($users, $roleId) {
    return $users->pluck('user_id');
})->all();

Conclusion

By following the above steps and examples, you can now retrieve user IDs from your Laravel application's belongsToMany relationships efficiently. While this process might seem a little convoluted, it ensures that only the data needed is returned, resulting in faster response times for your Laravel application and cleaner code.