Custom Laravel Relations?

Have you looked into the hasManyThrough relationship that Laravel offers?

Laravel HasManyThrough

It should help you retrieve all the permissions for a user.

The closest thing to a solution was what @biship posted in the comments. Where you would manually modify the properties of an existing Relation. This might work well in some scenarios. Really, it may be the right solution in some cases. However, I found I was having to strip down all of the constraints added by the Relation and manually add any new constraints I needed.

My thinking is this... If you're going to be stripping down the constraints each time so that the Relation is just "bare". Why not make a custom Relation that doesn't add any constraints itself and takes a Closure to help facilitate adding constraints?

Solution

Something like this seems to be working well for me. At least, this is the basic concept:

class Custom extends Relation
{
    protected $baseConstraints;

    public function __construct(Builder $query, Model $parent, Closure $baseConstraints)
    {
        $this->baseConstraints = $baseConstraints;

        parent::__construct($query, $parent);
    }

    public function addConstraints()
    {
        call_user_func($this->baseConstraints, $this);
    }

    public function addEagerConstraints(array $models)
    {
        // not implemented yet
    }

    public function initRelation(array $models, $relation)
    {
        // not implemented yet
    }

    public function match(array $models, Collection $results, $relation)
    {
        // not implemented yet
    }

    public function getResults()
    {
        return $this->get();
    }
}

The methods not implemented yet are used for eager loading and must be declared as they are abstract. I haven't that far yet. :)

And a trait to make this new Custom Relation easier to use.

trait HasCustomRelations
{
    public function custom($related, Closure $baseConstraints)
    {
        $instance = new $related;
        $query = $instance->newQuery();

        return new Custom($query, $this, $baseConstraints);
    }
}

Usage

// app/User.php
class User
{
    use HasCustomRelations;

    public function permissions()
    {
        return $this->custom(Permission::class, function ($relation) {
            $relation->getQuery()
                // join the pivot table for permission and roles
                ->join('permission_role', 'permission_role.permission_id', '=', 'permissions.id')
                // join the pivot table for users and roles
                ->join('role_user', 'role_user.role_id', '=', 'permission_role.role_id')
                // for this user
                ->where('role_user.user_id', $this->id);
        });
    }
}

// app/Permission.php
class Permission
{
    use HasCustomRelations;

    public function users()
    {
        return $this->custom(User::class, function ($relation) {
            $relation->getQuery()
                // join the pivot table for users and roles
                ->join('role_user', 'role_user.user_id', '=', 'users.id')
                // join the pivot table for permission and roles
                ->join('permission_role', 'permission_role.role_id', '=', 'role_user.role_id')
                // for this permission
                ->where('permission_role.permission_id', $this->id);
        });
    }
}

You could now do all the normal stuff for relations without having to query in-between relations first.

Github

I went a ahead and put all this on Github just in case there are more people who are interested in something like this. This is still sort of a science experiment in my opinion. But, hey, we can figure this out together. :)