Laravel Eloquent relationship examples based on http://www.sqlitetutorial.net/sqlite-sample-database/

Genre.php

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class Genre extends Model
{
  protected $primaryKey = 'GenreId';

  public function tracks()
  {
    return $this->hasMany('App\Track', 'GenreId');
  }
}

Playlist.php

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class Playlist extends Model
{
  protected $primaryKey = 'PlaylistId';

  public function tracks()
  {
    return $this->belongsToMany('App\Track', 'playlist_track', 'PlaylistId', 'TrackId');
  }
}

tinker.php

<?php

// all Metal tracks
Genre::find(3)->tracks;

// get the Metal genre from track 78 (Master of Puppets)
Track::find(78)->genre;
  
// Update a track's genre
Track::find(78)->genre()->associate(Genre::find(3));

// Many to Many relationships

// which playlists Master of Puppets is a part of
Track::find(78)->playlists;

// all tracks part of the Brazillian music playlist
Playlist::find(11)->tracks;

Track.php

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class Track extends Model
{
  protected $primaryKey = 'TrackId';

  public function genre()
  {
    return $this->belongsTo('App\Genre', 'GenreId');
  }

  public function playlists()
  {
    return $this->belongsToMany('App\Playlist', 'playlist_track', 'TrackId', 'PlaylistId');
  }
}