Laravel 5.8 is now released and one thing from the release notes many people might be waiting for is the hasOneThrough relationship. Laravel ealier had hasManyThrough, but with the addition of hasOneThrough it's more flexible. Let's dive into an example :

Consider we have User Model, Reviewer Model and Activity Model with structure :

users
    id - integer
    reviewer_id - integer

reviewers
    id - integer

activities
    id - integer
    user_id - integer

Each reviewer has one user, and each user is associated with one user activity record. If we want to get activity from reviewer, there is no reviewer_id column in activities table, in such case we can use hasOneThrough relation. Let's define the relationship now :

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class Reviewer extends Model
{
    /**
     * Get the reviewer's activity.
     */
    public function activity()
    {
        return $this->hasOneThrough('App\Activity', 'App\User');
    }
}

To understand more, lets use Laravel conventional terms on the models. In this case the Activity is the final model we would need to relate, while User is the intermediate model.

As all other relationships in Laravel, we can also explicitely specify the foreign keys while definining hasOneThrough relation, Let's do that for this example :

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class Reviewer extends Model
{
    /**
     * Get the reviewer's activity.
     */
    public function activity()
    {
        return $this->hasOneThrough(
            'App\Activity',
            'App\User',
            'reviewer_id', // Foreign key on users table...
            'user_id', // Foreign key on activities table...
            'id', // Local key on reviewers table...
            'id' // Local key on users table...
        );
    }
}

Now you can easily do :

$reviewer = Reviewer::first();
$activity = $reviewer->activity;