Laravel Eloquent Relationships

In this lesson, I will show you how to use Eloquent Relationships in laravel applications. I will show you how to build one-to-one, one-to-many, many-to-many, polymorphic relations across the laravel eloquent model class.

One to One:

$this->hasOne('App\Model');
$this->hasOne('App\Model', 'foreign_key', 'local_key');

One To One (Inverse): 

$this->belongsTo('App\Model');
$this->belongsTo('App\Model', 'foreign_key', 'other_key');

 One to Many:

$this->hasMany('App\Model');
$this->hasMany('App\Model', 'foreign_key', 'local_key');

One To Many (Inverse) 

$this->belongsTo('App\Model');
$this->belongsTo('App\Model', 'foreign_key', 'other_key');

Many to Many:

$this->belongsToMany('App\Model', 'pivot_table', 'foreign_id', 'foreign_id');

Example:

$this->belongsToMany('App\Role', 'role_user', 'user_id', 'role_id');

Attaching / Detaching:

Attaching:

$user->roles()->attach($roleId);
$user->roles()->attach($roleId, ['expires' => $expires]);

$user->roles()->attach([
    1 => ['expires' => $expires],
    2 => ['expires' => $expires],
]);

Detaching:

// Detach a single role from the user...
$user->roles()->detach($roleId);

// Detach all roles from the user...
$user->roles()->detach();


$user->roles()->detach([1, 2, 3]);

Syncing Associations:

$user->roles()->sync([1, 2, 3]);

Has One Through:

$this->hasOneThrough(
            'App\Owner',
            'App\Car',
            'mechanic_id', // Foreign key on cars table...
            'car_id', // Foreign key on owners table...
            'id', // Local key on mechanics table...
            'id' // Local key on cars table...
        );

mechanics
    id - integer
    name - string

cars
    id - integer
    model - string
    mechanic_id - integer

owners
    id - integer
    name - string
    car_id - integer

Has Many Through:

$this->hasManyThrough(
    'App\Post',
    'App\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...
);

countries
    id - integer
    name - string

users
    id - integer
    country_id - integer
    name - string

posts
    id - integer
    user_id - integer
    title - string

Polymorphic Relationships

One To One (Polymorphic):

posts
    id - integer
    name - string

users
    id - integer
    name - string

images
    id - integer
    url - string
    imageable_id - integer
    imageable_type - string

Models:

namespace App;

use Illuminate\Database\Eloquent\Model;

class Image extends Model
{
    /**
     * Get the owning imageable model.
     */
    public function imageable()
    {
        return $this->morphTo();
    }
}


class Post extends Model
{
    /**
     * Get the post's image.
     */
    public function image()
    {
        return $this->morphOne('App\Image', 'imageable');
    }
}


class User extends Model
{
    /**
     * Get the user's image.
     */
    public function image()
    {
        return $this->morphOne('App\Image', 'imageable');
    }
}

One To Many (Polymorphic):

posts
    id - integer
    title - string
    body - text

videos
    id - integer
    title - string
    url - string

comments
    id - integer
    body - text
    commentable_id - integer
    commentable_type - string

Models:

namespace App;

use Illuminate\Database\Eloquent\Model;

class Comment extends Model
{
    /**
     * Get the owning commentable model.
     */
    public function commentable()
    {
        return $this->morphTo();
    }
}


class Post extends Model
{
    /**
     * Get all of the post's comments.
     */
    public function comments()
    {
        return $this->morphMany('App\Comment', 'commentable');
    }
}


class Video extends Model
{
    /**
     * Get all of the video's comments.
     */
    public function comments()
    {
        return $this->morphMany('App\Comment', 'commentable');
    }
}