Example how to use HasManyThrough Relationship in Laravel

The "has-many-through" relationship provides a convenient shortcut for accessing distant relations via an intermediate relation. For example, a Country model might have many Post models through an intermediate User model. In this example, you could easily gather all blog posts for a given country. Let's look at the tables required to define this relationship:

countries
    id - integer
    name - string

users
    id - integer
    country_id - integer
    name - string

posts
    id - integer
    user_id - integer
    title - string

Though posts does not contain a country_id column, the hasManyThrough relation provides access to a country's posts via $country->posts. To perform this query, Eloquent inspects the country_id on the intermediate users table. After finding the matching user IDs, they are used to query the posts table.

Now that we have examined the table structure for the relationship, let's define it on the Country model:

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Model;

class Country extends Model
{
    /**
     * Get all of the posts for the country.
     */
    public function posts()
    {
        return $this->hasManyThrough('App\Models\Post', 'App\Models\User');
    }
}

The first argument passed to the hasManyThrough method is the name of the final model we wish to access, while the second argument is the name of the intermediate model.

Typical Eloquent foreign key conventions will be used when performing the relationship's queries. If you would like to customize the keys of the relationship, you may pass them as the third and fourth arguments to the hasManyThrough method. The third argument is the name of the foreign key on the intermediate model. The fourth argument is the name of the foreign key on the final model. The fifth argument is the local key, while the sixth argument is the local key of the intermediate model:

class Country extends Model
{
    public function posts()
    {
        return $this->hasManyThrough(
            'App\Models\Post',
            'App\Models\User',
            'country_id', // Foreign key on users table...
            'user_id', // Foreign key on posts table...
            'id', // Local key on countries table...
            'id' // Local key on users table...
        );
    }
}

Example how to use this relationship:

$country = Country::find(1);

dd($country->posts);

Example 2:

Let us say we have three models.

1. Team (id, name)
2. User (id, name, team_id)
3. Goal (id, user_id)

Now, inside User.php file. we can define the following relationships.

1. User hasMany Goals.
2. User belongsTo Team.

// User.php

public function goals()
{
    return $this->hasMany(Goal::class);
}

public function team()
{
    return $this->belongsTo(Team::class);
}

Next step inside Goal.php file, we can define the following relationship.

1. Goal belongsTo User

// Goal.php

public function user()
{
     return $this->belongsTo(User::class);
}

Finally, inside Team.php, we can define the following relationship.

1. Team hasMany User

// Team.php


public function users()
{
     return $this->hasMany(User::class);
}

the goal_id is not associated directly with the Team model.

The goal_id associated with the User model.

So, to get all goals of a team we can collect all the goals through the User model.

In that case, we can define the relationship like below inside Team.php model.

// Team.php

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class Team extends Model
{
    public function users()
    {
        return $this->hasMany(User::class);
    }

    public function goals()
    {
        return $this->hasManyThrough(Goal::class, User::class);
    }
}

Example how to get goals from team:

<?php

namespace App\Http\Controllers;

use Illuminate\Http\Request;
use App\Team;

class TeamController extends Controller
{
    public function show(Team $team)
    {
        $goals = $team->goals()->get();
    }
}