Laravel Lighthouse GraphQL query data from a pivot table that connects three tables

Question

In Laravel Lighthouse GraphQL, how can you retrieve the information from an intermediate "pivot" table?

Suppose I have Users and Roles in a belongsToMany relation:

type User {
  roles: [Role!]! @belongsToMany
}

type Role {
  users: [User!]! @belongsToMany
}

type Query {
    user(id: ID! @eq): User @find
    role(id: ID! @eq): Role @find
}

And also suppose that the intermediate table User_Role contains columns "created_at" and "tag_id".
How would I go about to include the "created_at" in my query?
How would I get the tag that the tag_id refers to?

Answer 1

I found out that you can do it like this:

First, make sure that the relation in the User model calls ->withPivot('created_at', 'tag_id'):

class User extends Model {
    public function roles(): BelongsToMany
    {
        return $this->belongsToMany(\App\Models\Role::class, 'User_Role')
                    ->using(User_Role::class) // only needed to retrieve the tag from the tag_id
                    ->withPivot('created_at', 'tag_id');
    } 
}

Create a class for the intermediate table that extends Pivot:

class User_Role extends Pivot
{
    public function tag(): BelongsTo
    {
        return $this->belongsTo(\App\Models\Tag::class, 'tag_id');
    }
}

Now change the GraphQL code as follows:

type User {
    id: ID!
    roles: [Role!] @belongsToMany
}

type Role {
    id: ID!
    pivot: UserRolePivot # this is where the magic happens
}

type UserRolePivot {
    created_at: Date!
    tag: Tag! @belongsTo
}

type Tag {
    id: ID!
    name: String!
}

And now you can query like this:

{
  users {
    id
    roles {
      id
      pivot {
        created_at
        tag {
          id
          name
        }
      }
    }
  }
}