Eloquent: Relationships

• Introduction
• Defining Relationships
  • One To One
  • One To Many
  • One To Many (Inverse)
  • Many To Many
  • Has Many Through
  • Polymorphic Relations
  • Many To Many Polymorphic Relations
• Querying Relations
  • Relationship Methods Vs. Dynamic Properties
  • Querying Relationship Existence
  • Querying Relationship Absence
  • Counting Related Models
• Eager Loading
  • Constraining Eager Loads
  • Lazy Eager Loading
• Inserting & Updating Related Models
  • The save Method
  • The create Method
  • Belongs To Relationships
  • Many To Many Relationships
• Touching Parent Timestamps

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

Defining Relationships

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:

<?php

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:

<?php

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:

/**
 * Get the user that owns the phone.
 */
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:

/**
 * Get the user that owns the phone.
 */
public function user()
{
    return $this->belongsTo('App\User', 'foreign_key', 'other_key');
}

Default Models

The belongsTo relationship allows you to define a default model that will be returned if the given relationship is null. This pattern is often referred to as the Null Object pattern and can help remove conditional checks in your code. In the following example, the user relation will return an empty App\User model if no user is attached to the post:

/**
 * Get the author of the post.
 */
public function user()
{
    return $this->belongsTo('App\User')->withDefault();
}

To populate the default model with attributes, you may pass an array or Closure to the withDefault method:

/**
 * Get the author of the post.
 */
public function user()
{
    return $this->belongsTo('App\User')->withDefault([
        'name' => 'Guest Author',
    ]);
}

/**
 * Get the author of the post.
 */
public function user()
{
    return $this->belongsTo('App\User')->withDefault(function ($user) {
        $user->name = 'Guest Author';
    });
}

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:

<?php

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:

$comments = App\Post::find(1)->comments()->where('title', 'foo')->first();

Like the hasOne method, you may also override the foreign and local keys by passing additional arguments to the hasMany method:

return $this->hasMany('App\Comment', 'foreign_key');

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

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:

<?php

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');
    }
}

Once the relationship has been defined, we can retrieve the Post model for a Comment by accessing the post "dynamic property":

$comment = App\Comment::find(1);

echo $comment->post->title;

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 _id. 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:

/**
 * Get the post that owns the comment.
 */
public function post()
{
    return $this->belongsTo('App\Post', '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:

/**
 * Get the post that owns the comment.
 */
public function post()
{
    return $this->belongsTo('App\Post', 'foreign_key', 'other_key');
}

Many To Many

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:

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class User extends Model
{
    /**
     * The roles that belong to the user.
     */
    public function roles()
    {
        return $this->belongsToMany('App\Role');
    }
}

Once the relationship is defined, you may access the user's roles using the roles dynamic property:

$user = App\User::find(1);

foreach ($user->roles as $role) {
    //
}

Of course, like all other relationship types, you may call the roles method to continue chaining query constraints onto the relationship:

$roles = App\User::find(1)->roles()->orderBy('name')->get();

As mentioned previously, to determine the table name of the relationship's joining table, Eloquent will join the two related model names in alphabetical order. However, you are free to override this convention. You may do so by passing a second argument to the belongsToMany method:

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

In addition to customizing the name of the joining table, you may also customize the column names of the keys on the table by passing additional arguments to the belongsToMany method. The third argument is the foreign key name of the model on which you are defining the relationship, while the fourth argument is the foreign key name of the model that you are joining to:

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

Defining The Inverse Of The Relationship

To define the inverse of a many-to-many relationship, you simply 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:

<?php

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');
    }
}

As you can see, the relationship is defined exactly the same as its User counterpart, with the exception of simply referencing the App\User model. Since we're reusing the belongsToMany method, all of the usual table and key customization options are available when defining the inverse of many-to-many relationships.

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;
}

Notice that each Role model we retrieve is automatically assigned a pivot attribute. This attribute contains a model representing the intermediate table, and may be used like any other Eloquent model.

By default, only the model keys will be present on the pivot object. If your pivot table contains extra attributes, you must specify them when defining the relationship:

return $this->belongsToMany('App\Role')->withPivot('column1', 'column2');

If you want your pivot table to have automatically maintained created_at and updated_at timestamps, use the withTimestamps method on the relationship definition:

return $this->belongsToMany('App\Role')->withTimestamps();

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:

return $this->belongsToMany('App\Podcast')
                ->as('subscription')
                ->withTimestamps();

Once this is done, you may access the intermediate table data using the customized name:

$users = User::with('podcasts')->get();

foreach ($users->flatMap->podcasts as $podcast) {
    echo $podcast->subscription->created_at;
}

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]);

Defining Custom Intermediate Table Models

If you would like to define a custom model to represent the intermediate table of your relationship, you may call the using method when defining the relationship. All custom models used to represent intermediate tables of relationships must extend the Illuminate\Database\Eloquent\Relations\Pivot class. For example, we may define a Role which uses a custom UserRole pivot model:

<?php

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');
    }
}

When defining the UserRole model, we will extend the Pivot class:

<?php

namespace App;

use Illuminate\Database\Eloquent\Relations\Pivot;

class UserRole extends Pivot
{
    //
}

Has Many Through

The "has-many-through" relationship provides a convenient shortcut for accessing distant relations via an intermediate relation. For example, a Country model might have many Post models through an intermediate User model. In this example, you could easily gather all blog posts for a given country. Let's look at the tables required to define this relationship:

countries
    id - integer
    name - string

users
    id - integer
    country_id - integer
    name - string

posts
    id - integer
    user_id - integer
    title - string

Though posts does not contain a country_id column, the hasManyThrough relation provides access to a country's posts via $country->posts. To perform this query, Eloquent inspects the country_id on the intermediate users table. After finding the matching user IDs, they are used to query the posts table.

Now that we have examined the table structure for the relationship, let's define it on the Country model:

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class Country extends Model
{
    /**
     * Get all of the posts for the country.
     */
    public function posts()
    {
        return $this->hasManyThrough('App\Post', 'App\User');
    }
}

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...
        );
    }
}

Polymorphic Relations

Table Structure

Polymorphic relations allow a model to belong to more than one other model on a single association. For example, imagine users of your application can "comment" both posts and videos. Using polymorphic relationships, you can use a single comments table for both of these scenarios. First, let's examine the table structure required to build this relationship:

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

Two important columns to note are the commentable_id and commentable_type columns on the comments table. The commentable_id column will contain the ID value of the post or video, while the commentable_type column will contain the class name of the owning model. The commentable_type column is how the ORM determines which "type" of owning model to return when accessing the commentable relation.

Model Structure

Next, let's examine the model definitions needed to build this relationship:

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class Comment extends Model
{
    /**
     * Get all of the owning commentable models.
     */
    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');
    }
}

Retrieving Polymorphic Relations

Once your database table and models are defined, you may access the relationships via your models. For example, to access all of the comments for a post, we can simply use the comments dynamic property:

$post = App\Post::find(1);

foreach ($post->comments as $comment) {
    //
}

You may also retrieve the owner of a polymorphic relation from the polymorphic model by accessing the name of the method that performs the call to morphTo. In our case, that is the commentable method on the Comment model. So, we will access that method as a dynamic property:

$comment = App\Comment::find(1);

$commentable = $comment->commentable;

The commentable relation on the Comment model will return either a Post or Video instance, depending on which type of model owns the comment.

Custom Polymorphic Types

By default, Laravel will use the fully qualified class name to store the type of the related model. For instance, given the example above where a Comment may belong to a Post or a Video, the default commentable_type would be either App\Post or App\Video, respectively. However, you may wish to decouple your database from your application's internal structure. In that case, you may define a relationship "morph map" to instruct Eloquent to use a custom name for each model instead of the class name:

use Illuminate\Database\Eloquent\Relations\Relation;

Relation::morphMap([
    'posts' => 'App\Post',
    'videos' => 'App\Video',
]);

You may register the morphMap in the boot function of your AppServiceProvider or create a separate service provider if you wish.

Many To Many Polymorphic Relations

Table Structure

In addition to traditional polymorphic relations, you may also define "many-to-many" polymorphic relations. For example, a blog Post and Video model could share a polymorphic relation to a Tag model. Using a many-to-many polymorphic relation allows you to have a single list of unique tags that are shared across blog posts and videos. First, let's examine the table structure:

posts
    id - integer
    name - string

videos
    id - integer
    name - string

tags
    id - integer
    name - string

taggables
    tag_id - integer
    taggable_id - integer
    taggable_type - string

Model Structure

Next, we're ready to define the relationships on the model. The Post and Video models will both have a tags method that calls the morphToMany method on the base Eloquent class:

<?php

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');
    }
}

Defining The Inverse Of The Relationship

Next, on the Tag model, you should define a method for each of its related models. So, for this example, we will define a posts method and a videos method:

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class Tag extends Model
{
    /**
     * Get all of the posts that are assigned this tag.
     */
    public function posts()
    {
        return $this->morphedByMany('App\Post', 'taggable');
    }

    /**
     * Get all of the videos that are assigned this tag.
     */
    public function videos()
    {
        return $this->morphedByMany('App\Video', 'taggable');
    }
}

Retrieving The Relationship

Once your database table and models are defined, you may access the relationships via your models. For example, to access all of the tags for a post, you can simply use the tags dynamic property:

$post = App\Post::find(1);

foreach ($post->tags as $tag) {
    //
}

You may also retrieve the owner of a polymorphic relation from the polymorphic model by accessing the name of the method that performs the call to morphedByMany. In our case, that is the posts or videos methods on the Tag model. So, you will access those methods as dynamic properties:

$tag = App\Tag::find(1);

foreach ($tag->videos as $video) {
    //
}

Querying Relations

Since all types of Eloquent relationships are defined via methods, you may call those methods to obtain an instance of the relationship without actually executing the relationship queries. In addition, all types of Eloquent relationships also serve as query builders, allowing you to continue to chain constraints onto the relationship query before finally executing the SQL against your database.

For example, imagine a blog system in which a User model has many associated Post models:

<?php

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');
    }
}

You may query the posts relationship and add additional constraints to the relationship like so:

$user = App\User::find(1);

$user->posts()->where('active', 1)->get();

You are able to use any of the query builder methods on the relationship, so be sure to explore the query builder documentation to learn about all of the methods that are available to you.

Relationship Methods Vs. Dynamic Properties

If you do not need to add additional constraints to an Eloquent relationship query, you may simply access the relationship as if it were a property. For example, continuing to use our User and Post example models, we may access all of a user's posts like so:

$user = App\User::find(1);

foreach ($user->posts as $post) {
    //
}

Dynamic properties are "lazy loading", meaning they will only load their relationship data when you actually access them. Because of this, developers often use eager loading to pre-load relationships they know will be accessed after loading the model. Eager loading provides a significant reduction in SQL queries that must be executed to load a model's relations.

Querying Relationship Existence

When accessing the records for a model, you may wish to limit your results based on the existence of a relationship. For example, imagine you want to retrieve all blog posts that have at least one comment. To do so, you may pass the name of the relationship to the has and orHas methods:

// Retrieve all posts that have at least one comment...
$posts = App\Post::has('comments')->get();

You may also specify an operator and count to further customize the query:

// Retrieve all posts that have three or more comments...
$posts = Post::has('comments', '>=', 3)->get();

Nested has statements may also be constructed using "dot" notation. For example, you may retrieve all posts that have at least one comment and vote:

// Retrieve all posts that have at least one comment with votes...
$posts = Post::has('comments.votes')->get();

If you need even more power, you may use the whereHas and orWhereHas methods to put "where" conditions on your has queries. These methods allow you to add customized constraints to a relationship constraint, such as checking the content of a comment:

// Retrieve all posts with at least one comment containing words like foo%
$posts = Post::whereHas('comments', function ($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:

$posts = App\Post::doesntHave('comments')->get();

If you need even more power, you may use the whereDoesntHave and orWhereDoesntHave methods to put "where" conditions on your doesntHave queries. These methods allows you to add customized constraints to a relationship constraint, such as checking the content of a comment:

$posts = Post::whereDoesntHave('comments', function ($query) {
    $query->where('content', 'like', 'foo%');
})->get();

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;
}

You may add the "counts" for multiple relations as well as add constraints to the queries:

$posts = Post::withCount(['votes', 'comments' => function ($query) {
    $query->where('content', 'like', 'foo%');
}])->get();

echo $posts[0]->votes_count;
echo $posts[0]->comments_count;

You may also alias the relationship count result, allowing multiple counts on the same relationship:

$posts = Post::withCount([
    'comments',
    'comments as pending_comments_count' => function ($query) {
        $query->where('approved', false);
    }
])->get();

echo $posts[0]->comments_count;

echo $posts[0]->pending_comments_count;

Eager Loading

When accessing Eloquent relationships as properties, the relationship data is "lazy loaded". This means the relationship data is not actually loaded until you first access the property. However, Eloquent can "eager load" relationships at the time you query the parent model. Eager loading alleviates the N + 1 query problem. To illustrate the N + 1 query problem, consider a Book model that is related to Author:

<?php

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');
    }
}

Now, let's retrieve all books and their authors:

$books = App\Book::all();

foreach ($books as $book) {
    echo $book->author->name;
}

This loop will execute 1 query to retrieve all of the books on the table, then another query for each book to retrieve the author. So, if we have 25 books, this loop would run 26 queries: 1 for the original book, and 25 additional queries to retrieve the author of each book.

Thankfully, we can use eager loading to reduce this operation to just 2 queries. When querying, you may specify which relationships should be eager loaded using the with method:

$books = App\Book::with('author')->get();

foreach ($books as $book) {
    echo $book->author->name;
}

For this operation, only two queries will be executed:

select * from books

select * from authors where id in (1, 2, 3, 4, 5, ...)

Eager Loading Multiple Relationships

Sometimes you may need to eager load several different relationships in a single operation. To do so, just pass additional arguments to the with method:

$books = App\Book::with(['author', 'publisher'])->get();

Nested Eager Loading

To eager load nested relationships, you may use "dot" syntax. For example, let's eager load all of the book's authors and all of the author's personal contacts in one Eloquent statement:

$books = App\Book::with('author.contacts')->get();

Eager Loading Specific Columns

You may not always need every column from the relationships you are retrieving. For this reason, Eloquent allows you to specify which columns of the relationship you would like to retrieve:

$users = App\Book::with('author:id,name')->get();

{note} When using this feature, you should always include the id column in the list of columns you wish to retrieve.

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:

$users = App\User::with(['posts' => function ($query) {
    $query->where('title', 'like', '%first%');
}])->get();

In this example, Eloquent will only eager load posts where the post's title column contains the word first. Of course, you may call other query builder methods to further customize the eager loading operation:

$users = App\User::with(['posts' => function ($query) {
    $query->orderBy('created_at', 'desc');
}])->get();

Lazy Eager Loading

Sometimes you may need to eager load a relationship after the parent model has already been retrieved. For example, this may be useful if you need to dynamically decide whether to load related models:

$books = App\Book::all();

if ($someCondition) {
    $books->load('author', 'publisher');
}

If you need to set additional query constraints on the eager loading query, you may pass an array keyed by the relationships you wish to load. The array values should be Closure instances which receive the query instance:

$books->load(['author' => function ($query) {
    $query->orderBy('published_date', 'asc');
}]);

To load a relationship only when it has not already been loaded, use the loadMissing method:

public function format(Book $book)
{
    $book->loadMissing('author');

    return [
        'name' => $book->name,
        'author' => $book->author->name
    ];
}

Inserting & Updating Related Models

The Save Method

Eloquent provides convenient methods for adding new models to relationships. For example, perhaps you need to insert a new Comment for a Post model. Instead of manually setting the post_id attribute on the Comment, you may insert the Comment directly from the relationship's save method:

$comment = new App\Comment(['message' => 'A new comment.']);

$post = App\Post::find(1);

$post->comments()->save($comment);

Notice that we did not access the comments relationship as a dynamic property. Instead, we called the comments method to obtain an instance of the relationship. The save method will automatically add the appropriate post_id value to the new Comment model.

If you need to save multiple related models, you may use the saveMany method:

$post = App\Post::find(1);

$post->comments()->saveMany([
    new App\Comment(['message' => 'A new comment.']),
    new App\Comment(['message' => 'Another comment.']),
]);

The Create Method

In addition to the save and saveMany methods, you may also use the create method, which accepts an array of attributes, creates a model, and inserts it into the database. Again, the difference between save and create is that save accepts a full Eloquent model instance while create accepts a plain PHP array:

$post = App\Post::find(1);

$comment = $post->comments()->create([
    'message' => 'A new comment.',
]);

{tip} Before using the create method, be sure to review the documentation on attribute mass assignment.

You may use the createMany method to create multiple related models:

$post = App\Post::find(1);

$post->comments()->createMany([
    [
        'message' => 'A new comment.',
    ],
    [
        'message' => 'Another new comment.',
    ],
]);

Belongs To Relationships

When updating a belongsTo relationship, you may use the associate method. This method will set the foreign key on the child model:

$account = App\Account::find(10);

$user->account()->associate($account);

$user->save();

When removing a belongsTo relationship, you may use the dissociate method. This method will set the relationship's foreign key to null:

$user->account()->dissociate();

$user->save();

Many To Many Relationships

Attaching / Detaching

Eloquent also provides a few additional helper methods to make working with related models more convenient. For example, let's imagine a user can have many roles and a role can have many users. To attach a role to a user by inserting a record in the intermediate table that joins the models, use the attach method:

$user = App\User::find(1);

$user->roles()->attach($roleId);

When attaching a relationship to a model, you may also pass an array of additional data to be inserted into the intermediate table:

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

Of course, sometimes it may be necessary to remove a role from a user. To remove a many-to-many relationship record, use the detach method. The detach method will remove the appropriate record out of the intermediate table; however, both models will remain in the database:

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

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

For convenience, attach and detach also accept arrays of IDs as input:

$user = App\User::find(1);

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

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

Syncing Associations

You may also use the sync method to construct many-to-many associations. The sync method accepts an array of IDs to place on the intermediate table. Any IDs that are not in the given array will be removed from the intermediate table. So, after this operation is complete, only the IDs in the given array will exist in the intermediate table:

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

You may also pass additional intermediate table values with the IDs:

$user->roles()->sync([1 => ['expires' => true], 2, 3]);

If you do not want to detach existing IDs, you may use the syncWithoutDetaching method:

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

Toggling Associations

The many-to-many relationship also provides a toggle method which "toggles" the attachment status of the given IDs. If the given ID is currently attached, it will be detached. Likewise, if it is currently detached, it will be attached:

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

Saving Additional Data On A Pivot Table

When working with a many-to-many relationship, the save method accepts an array of additional intermediate table attributes as its second argument:

App\User::find(1)->roles()->save($role, ['expires' => $expires]);

Updating A Record On A Pivot Table

If you need to update an existing row in your pivot table, you may use updateExistingPivot method. This method accepts the pivot record foreign key and an array of attributes to update:

$user = App\User::find(1);

$user->roles()->updateExistingPivot($roleId, $attributes);

Touching Parent Timestamps

When a model belongsTo or belongsToMany another model, such as a Comment which belongs to a Post, it is sometimes helpful to update the parent's timestamp when the child model is updated. For example, when a Comment model is updated, you may want to automatically "touch" the updated_at timestamp of the owning Post. Eloquent makes it easy. Just add a touches property containing the names of the relationships to the child model:

<?php

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');
    }
}

Now, when you update a Comment, the owning Post will have its updated_at column updated as well, making it more convenient to know when to invalidate a cache of the Post model:

$comment = App\Comment::find(1);

$comment->text = 'Edit to this comment!';

$comment->save();