Laravel Eloquent Relationship Types and Usage Guide

Laravel's Eloquent ORM provides a set of relationship methods that make working with related database tables simple and expressive. The most common relationship types are one-to-one, one-to-many, many-to-many, polymorphic, and has‑many‑through.

Defining relationships is done by adding methods to the model class that return the appropriate relation object (e.g., hasOne , hasMany , belongsTo , belongsToMany , morphOne , morphMany , hasManyThrough ). These methods can be chained with query constraints just like a normal query builder.

hasOne('App\Phone');
    }
}
?>

The hasOne example above creates a one‑to‑one link between User and Phone . The foreign key defaults to user_id on the Phone table, but a custom key can be supplied as a second argument.

belongsTo('App\User');
    }
}
?>

One‑to‑many relationships are defined with hasMany . For example, a Post model may have many Comment models:

hasMany('App\Comment');
    }
}
?>

Many‑to‑many relationships use belongsToMany and require a pivot table. The example below shows a User model that can belong to many Role models:

belongsToMany('App\Role');
    }
}
?>

Polymorphic relationships allow a model to belong to more than one other model on a single association. The Comment model can belong to either a Post or a Video :

morphTo();
    }
}

class Post extends Model
{
    public function comments()
    {
        return $this->morphMany('App\Comment', 'commentable');
    }
}

class Video extends Model
{
    public function comments()
    {
        return $this->morphMany('App\Comment', 'commentable');
    }
}
?>

When querying, relationships can be used as query builders to add constraints, count related records, or filter based on existence. Examples include has , whereHas , doesntHave , and withCount methods.

$posts = Post::has('comments')->get();
$posts = Post::whereHas('comments', function ($q) {
    $q->where('content', 'like', 'foo%');
})->get();
$posts = Post::withCount('comments')->get();

Eloquent also supports eager loading with with to avoid N+1 query problems, nested eager loading using dot notation, and constrained eager loading using closures.

$books = Book::with(['author', 'publisher'])->get();
$books = Book::with('author.contacts')->get();
$users = User::with(['posts' => function ($q) {
    $q->where('title', 'like', '%first%');
}])->get();

Inserting or updating related models can be done with save , saveMany , create , createMany , as well as association helpers like associate and dissociate for belongsTo relations. For many‑to‑many pivots, methods such as attach , detach , sync , toggle , and updateExistingPivot manage pivot records and extra attributes.

$user->roles()->attach($roleId, ['expires' => $expires]);
$user->roles()->detach($roleId);
$user->roles()->sync([1, 2, 3]);
$user->roles()->toggle([1, 2]);
$user->roles()->updateExistingPivot($roleId, ['expires' => true]);

Finally, the $touches property on a model can be used to automatically update the updated_at timestamp of related parent models when the child model is saved, keeping caches in sync.