Introduction
Database tables are often related to one another. For example, a blog post may have many comments, or an order could be related to the user who placed it. Eloquent makes managing and working with these relationships easy, and supports several different types of relationships:
One To One
One To Many
Many To Many
Has Many Through
Polymorphic Relations
Many To Many Polymorphic Relations
Eloquent relationships are defined as methods on your Eloquent model classes. Since, like Eloquent models themselves, relationships also serve as powerful query builders, defining relationships as methods provides powerful method chaining and querying capabilities. For example, we may chain additional constraints on this posts relationship:
$user->posts()->where(‘active’, 1)->get();
But, before diving too deep into using relationships, let’s learn how to define each type.
One To One
A one-to-one relationship is a very basic relation. For example, a User model might be associated with one Phone. To define this relationship, we place a phone method on the User model. The phone method should call the hasOne method and return its result:
namespace App;
use Illuminate\Database\Eloquent\Model;
class User extends Model
{
/**
* Get the phone record associated with the user.
*/
public function phone()
{
return $this->hasOne('App\Phone');
}
}
The first argument passed to the hasOne method is the name of the related model. Once the relationship is defined, we may retrieve the related record using Eloquent’s dynamic properties. Dynamic properties allow you to access relationship methods as if they were properties defined on the model:
$phone = User::find(1)->phone;
Eloquent determines the foreign key of the relationship based on the model name. In this case, the Phone model is automatically assumed to have a user_id foreign key. If you wish to override this convention, you may pass a second argument to the hasOne method:
return $this->hasOne(‘App\Phone’, ‘foreign_key’);
Additionally, Eloquent assumes that the foreign key should have a value matching the id (or the custom $primaryKey) column of the parent. In other words, Eloquent will look for the value of the user’s id column in the user_id column of the Phone record. If you would like the relationship to use a value other than id, you may pass a third argument to the hasOne method specifying your custom key:
return $this->hasOne(‘App\Phone’, ‘foreign_key’, ‘local_key’);
Defining The Inverse Of The Relationship
So, we can access the Phone model from our User. Now, let’s define a relationship on the Phone model that will let us access the User that owns the phone. We can define the inverse of a hasOne relationship using the belongsTo method:
namespace App;
use Illuminate\Database\Eloquent\Model;
class Phone extends Model
{
/**
* Get the user that owns the phone.
*/
public function user()
{
return $this->belongsTo('App\User');
}
}
In the example above, Eloquent will try to match the user_id from the Phone model to an id on the User model. Eloquent determines the default foreign key name by examining the name of the relationship method and suffixing the method name with _id. However, if the foreign key on the Phone model is not user_id, you may pass a custom key name as the second argument to the belongsTo method:
public function user()
{
return $this->belongsTo('App\User', 'foreign_key');
}
If your parent model does not use id as its primary key, or you wish to join the child model to a different column, you may pass a third argument to the belongsTo method specifying your parent table’s custom key:
public function user()
{
return $this->belongsTo('App\User', 'foreign_key', 'other_key');
}
One To Many
A “one-to-many” relationship is used to define relationships where a single model owns any amount of other models. For example, a blog post may have an infinite number of comments. Like all other Eloquent relationships, one-to-many relationships are defined by placing a function on your Eloquent model:
namespace App;
use Illuminate\Database\Eloquent\Model;
class Post extends Model
{
/**
* Get the comments for the blog post.
*/
public function comments()
{
return $this->hasMany('App\Comment');
}
}
Remember, Eloquent will automatically determine the proper foreign key column on the Comment model. By convention, Eloquent will take the “snake case” name of the owning model and suffix it with _id. So, for this example, Eloquent will assume the foreign key on the Comment model is post_id.
Once the relationship has been defined, we can access the collection of comments by accessing the comments property. Remember, since Eloquent provides “dynamic properties”, we can access relationship methods as if they were defined as properties on the model:
$comments = App\Post::find(1)->comments;
foreach ($comments as $comment) {
//
}
Of course, since all relationships also serve as query builders, you can add further constraints to which comments are retrieved by calling the comments method and continuing to chain conditions onto the query:
$comment = App\Post::find(1)->comments()->where('title', 'foo')->first();
One To Many (Inverse)
Now that we can access all of a post’s comments, let’s define a relationship to allow a comment to access its parent post. To define the inverse of a hasMany relationship, define a relationship function on the child model which calls the belongsTo method:
namespace App;
use Illuminate\Database\Eloquent\Model;
class Comment extends Model
{
/**
* Get the post that owns the comment.
*/
public function post()
{
return $this->belongsTo('App\Post');
}
}
In the example above, Eloquent will try to match the post_id from the Comment model to an id on the Post model. Eloquent determines the default foreign key name by examining the name of the relationship method and suffixing the method name with a _ followed by the name of the primary key column. However, if the foreign key on the Comment model is not post_id, you may pass a custom key name as the second argument to the belongsTo method:
public function post()
{
return $this->belongsTo('App\Post', 'foreign_key');
}
public function post()
{
return $this->belongsTo('App\Post', 'foreign_key', 'other_key');
}
Many-to-many relations are slightly more complicated than hasOne and hasMany relationships. An example of such a relationship is a user with many roles, where the roles are also shared by other users. For example, many users may have the role of “Admin”. To define this relationship, three database tables are needed: users, roles, and role_user. The role_user table is derived from the alphabetical order of the related model names, and contains the user_id and role_id columns.
Many-to-many relationships are defined by writing a method that returns the result of the belongsToMany method. For example, let’s define the roles method on our User model:
Defining The Inverse Of The Relationship
To define the inverse of a many-to-many relationship, you place another call to belongsToMany on your related model. To continue our user roles example, let’s define the users method on the Role model:
namespace App;
use Illuminate\Database\Eloquent\Model;
class Role extends Model
{
/**
* The users that belong to the role.
*/
public function users()
{
return $this->belongsToMany('App\User');
}
}
Retrieving Intermediate Table Columns
As you have already learned, working with many-to-many relations requires the presence of an intermediate table. Eloquent provides some very helpful ways of interacting with this table. For example, let’s assume our User object has many Role objects that it is related to. After accessing this relationship, we may access the intermediate table using the pivot attribute on the models:
$user = App\User::find(1);
foreach ($user->roles as $role) {
echo $role->pivot->created_at;
}
Customizing The pivot Attribute Name
As noted earlier, attributes from the intermediate table may be accessed on models using the pivot attribute. However, you are free to customize the name of this attribute to better reflect its purpose within your application.
For example, if your application contains users that may subscribe to podcasts, you probably have a many-to-many relationship between users and podcasts. If this is the case, you may wish to rename your intermediate table accessor to subscription instead of pivot. This can be done using the as method when defining the relationship:
Filtering Relationships Via Intermediate Table Columns
You can also filter the results returned by belongsToMany using the wherePivot and wherePivotIn methods when defining the relationship:
return $this->belongsToMany(‘App\Role’)->wherePivot(‘approved’, 1);
return $this->belongsToMany(‘App\Role’)->wherePivotIn(‘priority’, [1, 2]);
namespace App;
use Illuminate\Database\Eloquent\Model;
class Role extends Model
{
/**
* The users that belong to the role.
*/
public function users()
{
return $this->belongsToMany('App\User')->using('App\UserRole');
}
}
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\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...
);
}
}
use Illuminate\Database\Eloquent\Relations\Relation;
Relation::morphMap([
'posts' => 'App\Post',
'videos' => 'App\Video',
]);
namespace App;
use Illuminate\Database\Eloquent\Model;
class Post extends Model
{
/**
* Get all of the tags for the post.
*/
public function tags()
{
return $this->morphToMany('App\Tag', 'taggable');
}
}
namespace App;
use Illuminate\Database\Eloquent\Model;
class User extends Model
{
/**
* Get all of the posts for the user.
*/
public function posts()
{
return $this->hasMany('App\Post');
}
}
$user = App\User::find(1);
foreach ($user->posts as $post) {
//
}
$posts = App\Post::has('comments')->get();
$posts = App\Post::has('comments', '>=', 3)->get();
$posts = App\Post::has('comments.votes')->get();
$posts = App\Post::whereHas('comments', function ($query) {
$query->where('content', 'like', 'foo%');
})->get();
Querying Relationship Absence
When accessing the records for a model, you may wish to limit your results based on the absence of a relationship. For example, imagine you want to retrieve all blog posts that don’t have any comments. To do so, you may pass the name of the relationship to the doesntHave and orDoesntHave methods:
Counting Related Models
If you want to count the number of results from a relationship without actually loading them you may use the withCount method, which will place a {relation}_count column on your resulting models. For example:
$posts = App\Post::withCount('comments')->get();
foreach ($posts as $post) {
echo $post->comments_count;
}
$posts = App\Post::withCount(['votes', 'comments' => function ($query) {
$query->where('content', 'like', 'foo%');
}])->get();
echo $posts[0]->votes_count;
echo $posts[0]->comments_count;
namespace App;
use Illuminate\Database\Eloquent\Model;
class Book extends Model
{
/**
* Get the author that wrote the book.
*/
public function author()
{
return $this->belongsTo('App\Author');
}
}
Constraining Eager Loads
Sometimes you may wish to eager load a relationship, but also specify additional query constraints for the eager loading query. Here’s an example:
namespace App;
use Illuminate\Database\Eloquent\Model;
class Comment extends Model
{
/**
* All of the relationships to be touched.
*
* @var array
*/
protected $touches = ['post'];
/**
* Get the post that the comment belongs to.
*/
public function post()
{
return $this->belongsTo('App\Post');
}
}
