Belongs to many through

I wonder why this is not a part of laravel.

Let's say we have projects and categories that belongToMany each other. That's easy. Then we have campaigns that belong to one project, and we want them to have the same categories as their parent project. How do we do that?

campaigns:

id
title
project id

projects:

id
title

category_project:

category_id
project_id

Models

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Factories\HasFactory;
use Illuminate\Database\Eloquent\Model;

class Project extends Model
{
    use HasFactory;

    public function campaigns()
    {
        return $this->hasMany(Campaign::class);
    }

    public function categories()
    {
        return $this->belongsToMany(Category::class);
    }
}

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Factories\HasFactory;
use Illuminate\Database\Eloquent\Model;

class Category extends Model
{
    use HasFactory;

    public function campaigns()
    {
        return $this->belongsToMany(Campaign::class, 'category_project', null, 'project_id', null, 'project_id');
    }

    public function projects()
    {
        return $this->belongsToMany(Project::class);
    }
}

Note how the related keys on the belongsToMany relation are defined

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Factories\HasFactory;
use Illuminate\Database\Eloquent\Model;

class Campaign extends Model
{
    use HasFactory;

    public function categories()
    {
        return $this->belongsToMany(Category::class, 'category_project', 'project_id', null, 'project_id');
    }

    public function project()
    {
        return $this->belongsTo(Project::class);
    }
}

Note how the related keys on the belongsToMany relation are defined

Testing

<?php

// ./routes/web.php

use Illuminate\Support\Facades\Route;


Route::get('/', function () {
    return [
        'projects' => \App\Models\Project::with(['campaigns.categories'])->get(),
        'campaings' => \App\Models\Campaign::with(['project', 'categories'])->get(),
        'categories' => \App\Models\Category::with(['campaigns.project', 'projects.campaigns'])->get(),
    ];
});

4 likes

CItyTrader

2 years ago

Level 3

@rodrigo.pedra I know I'm super late. I just came across this and wow, it really works. Please can you explain how and why this works, I'm quite curious

mskhoshnazar

5 years ago

Level 1

Thank you, what a life saver!

1 like

rodrigo.pedra

5 years ago

Level 56

You’re welcome! Have a nice day =)