# Fluent ORM: Relationships

<Badge type="tip" vertical="top" text="Fluent Framework" /> <Badge type="warning" vertical="top" text="ORM" />


## 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. Fluent ORM makes managing and working with these relationships easy, and supports several types of relationships:

- `One To One`
- `One To Many`
- `Many To Many`
- `Has Many Through`
- `Polymorphic Relations`
- `Many To Many Polymorphic Relations`


## Defining Relationships

Fluent ORM relationships are defined as methods on your Fluent ORM model classes. Since, like Fluent ORM models themselves, relationships also serve as powerful <a href="/database/query-builder">query builders</a>, defining relationships as methods provides powerful method chaining and querying capabilities. For example, we may chain additional constraints on this `orders` relationship:
```php
$customer->orders()->where('status', 'paid')->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 `Customer` model might be associated with one `Address`. To define this relationship, we place a `address` method on the `Customer` model. The `address` method should call the `hasOne` method and return its result:
```php
<?php
 
namespace FluentCrm\App\Models;
 
use FluentCrm\Framework\Database\Orm\Model;
 
class Customer extends Model
{
    /**
     * Get the address record associated with the customer.
     */
    public function address()
    {
        return $this->hasOne('FluentCrm\App\Models\Address');
    }
}
```
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 Fluent ORM's dynamic properties. Dynamic properties allow you to access relationship methods as if they were properties defined on the model:
```php
$address = FluentCrm\App\Models\Customer::find(1)->address;
```
Fluent ORM determines the foreign key of the relationship based on the model name. In this case, the `Address` model is automatically assumed to have a `customer_id` foreign key. If you wish to override this convention, you may pass a second argument to the `hasOne` method:
```php
return $this->hasOne('FluentCrm\App\Models\Address', 'foreign_key');
```
Additionally, Fluent ORM assumes that the foreign key should have a value matching the `id` (or the custom `$primaryKey`) column of the parent. In other words, Fluent ORM will look for the value of the customer's `id` column in the `customer_id` column of the `Address` 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:
```php
return $this->hasOne('FluentCrm\App\Models\Address', 'foreign_key', 'local_key');
```

### Defining The Inverse Of The Relationship
So, we can access the `Address` model from our `Customer`. Now, let's define a relationship on the `Address` model that will let us access the `Customer` that owns the `address`. We can define the inverse of a `hasOne` relationship using the `belongsTo` method:
```php
<?php
 
namespace FluentCrm\App\Models;
 
use FluentCrm\Framework\Database\Orm\Model;
 
class Address extends Model
{
    /**
     * Get the customer record associated with the address.
     */
    public function customer()
    {
        return $this->belongsTo('FluentCrm\App\Models\Customer');
    }
}
```
In the example above, Fluent ORM will try to match the `customer_id` from the `Address` model to an id on the `Customer` model. Fluent ORM 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 `Address` model is not `customer_id`, you may pass a custom key name as the second argument to the `belongsTo` method:
```php
return $this->belongsTo('FluentCrm\App\Models\Customer', '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:
```php
return $this->belongsTo('FluentCrm\App\Models\Customer', '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 Fluent ORM relationships, one-to-many relationships are defined by placing a function on your Fluent ORM model:
```php
<?php
 
namespace FluentCrm\App\Models;
 
use FluentCrm\Framework\Database\Orm\Model;
 
class Post extends Model
{
    /**
     * Get the comments for the blog post.
     */
    public function comments()
    {
        return $this->hasMany('FluentCrm\App\Models\Comment');
    }
}
```
Remember, Fluent ORM will automatically determine the proper foreign key column on the `Comment` model. By convention, Fluent ORM will take the "snake case" name of the owning model and suffix it with `_id`. So, for this example, Fluent ORM 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 Fluent ORM provides "dynamic properties", we can access relationship methods as if they were defined as properties on the model:
```php
$comments = FluentCrm\App\Models\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:
```php
$comment = FluentCrm\App\Models\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
```php
return $this->hasMany('FluentCrm\App\Models\Comment', 'foreign_key');
 
return $this->hasMany('FluentCrm\App\Models\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
<?php
 
namespace FluentCrm\App\Models;
 
use FluentCrm\Framework\Database\Orm\Model;
 
class Comment extends Model
{
    /**
     * Get the post that owns the comment.
     */
    public function post()
    {
        return $this->belongsTo('FluentCrm\App\Models\Post');
    }
}
```
Once the relationship has been defined, we can retrieve the `Post` model for a `Comment` by accessing the `post` "dynamic property":
```php
$comment = FluentCrm\App\Models\Comment::find(1);
 
echo $comment->post->title;
```
In the example above, Fluent ORM will try to match the `post_id` from the `Comment` model to an `id` on the `Post` model. Fluent ORM 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:
```php
/**
 * Get the post that owns the comment.
 */
public function post()
{
    return $this->belongsTo('FluentCrm\App\Models\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:
```php
/**
 * Get the post that owns the comment.
 */
public function post()
{
    return $this->belongsTo('FluentCrm\App\Models\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
<?php
 
namespace FluentCrm\App\Models;
 
use FluentCrm\Framework\Database\Orm\Model;
 
class User extends Model
{
    /**
     * The roles that belong to the user.
     */
    public function roles()
    {
        return $this->belongsToMany('FluentCrm\App\Models\Role');
    }
}
```
Once the relationship is defined, you may access the user's roles using the `roles` dynamic property:
```php
$user = FluentCrm\App\Models\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:
```php
$roles = FluentCrm\App\Models\User::find(1)->roles()->orderBy('name')->get();
```
As mentioned previously, to determine the table name of the relationship's joining table, Fluent ORM 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:
```php
return $this->belongsToMany('FluentCrm\App\Models\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:
```php
return $this->belongsToMany('FluentCrm\App\Models\Role', 'role_user', 'user_id', 'role_id');
```

#### 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:
```php
<?php
 
namespace FluentCrm\App\Models;
 
use FluentCrm\Framework\Database\Orm\Model;
 
class Role extends Model
{
    /**
     * The users that belong to the role.
     */
    public function users()
    {
        return $this->belongsToMany('FluentCrm\App\Models\User');
    }
}
```
As you can see, the relationship is defined exactly the same as its User counterpart, with the exception of referencing the `FluentCrm\App\Models\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. Fluent ORM 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:
```php
$user = FluentCrm\App\Models\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 Fluent ORM 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:
```php
return $this->belongsToMany('FluentCrm\App\Models\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:
```php
return $this->belongsToMany('FluentCrm\App\Models\Role')->withTimestamps();
```

#### 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:
```php
return $this->belongsToMany('FluentCrm\App\Models\Role')->wherePivot('approved', 1);
 
return $this->belongsToMany('FluentCrm\App\Models\Role')->wherePivotIn('priority', [1, 2]);
```

### 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:
```php
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, Fluent ORM 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
<?php
 
namespace FluentCrm\App\Models;
 
use FluentCrm\Framework\Database\Orm\Model;
 
class Country extends Model
{
    /**
     * Get all the posts for the country.
     */
    public function posts()
    {
        return $this->hasManyThrough('FluentCrm\App\Models\Post', 'FluentCrm\App\Models\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 Fluent ORM 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:
```php
class Country extends Model
{
    public function posts()
    {
        return $this->hasManyThrough(
            'FluentCrm\App\Models\Post',
            'FluentCrm\App\Models\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" on 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:
```php
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
<?php
 
namespace FluentCrm\App\Models;
 
use FluentCrm\Framework\Database\Orm\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('FluentCrm\App\Models\Comment', 'commentable');
    }
}
 
class Video extends Model
{
    /**
     * Get all of the video's comments.
     */
    public function comments()
    {
        return $this->morphMany('FluentCrm\App\Models\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 the comments for a post, we can use the `comments` dynamic property:
```php
$post = FluentCrm\App\Models\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:
```php
$comment = FluentCrm\App\Models\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, Fluent Framework 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 `FluentCrm\App\Models\Post` or `FluentCrm\App\Models\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 Fluent ORM to use a custom name for each model instead of the class name:
```php
use FluentCrm\Framework\Database\Orm\Relations\Relation;
 
Relation::morphMap([
    'posts'  => 'FluentCrm\App\Models\Post',
    'videos' => 'FluentCrm\App\Models\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:
```php
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 Fluent ORM class:
```php
<?php
 
namespace FluentCrm\App\Models;
 
use FluentCrm\Framework\Database\Orm\Model;
 
class Post extends Model
{
    /**
     * Get all of the tags for the post.
     */
    public function tags()
    {
        return $this->morphToMany('FluentCrm\App\Models\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
<?php
 
namespace FluentCrm\App\Models;
 
use FluentCrm\Framework\Database\Orm\Model;
 
class Tag extends Model
{
    /**
     * Get all of the posts that are assigned this tag.
     */
    public function posts()
    {
        return $this->morphedByMany('FluentCrm\App\Models\Post', 'taggable');
    }
 
    /**
     * Get all of the videos that are assigned this tag.
     */
    public function videos()
    {
        return $this->morphedByMany('FluentCrm\App\Models\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 use the `tags` dynamic property:
```php
$post = FluentCrm\App\Models\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:
```php
$tag = FluentCrm\App\Models\Tag::find(1);
 
foreach ($tag->videos as $video) {
    //
}
```

### Querying Relations
Since all types of Fluent ORM 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 Fluent ORM relationships also serve as <a href="/database/query-builder">query builders</a>, 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
<?php
 
namespace FluentCrm\App\Models;
 
use FluentCrm\Framework\Database\Orm\Model;
 
class User extends Model
{
    /**
     * Get all of the posts for the user.
     */
    public function posts()
    {
        return $this->hasMany('FluentCrm\App\Models\Post');
    }
}
```
You may query the `posts` relationship and add additional constraints to the relationship like so:
```php
$user = FluentCrm\App\Models\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 <a href="/database/query-builder">query builders</a> documentation to learn about all the methods that are available to you.


### Relationship Methods Vs. Dynamic Properties
If you do not need to add additional constraints to an Fluent ORM relationship query, you may 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:
```php
$user = FluentCrm\App\Models\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. 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:
```php
// Retrieve all posts that have at least one comment...
$posts = FluentCrm\App\Models\Post::has('comments')->get();
```
You may also specify an operator and count to further customize the query:
```php
// Retrieve all posts that have three or more comments...
$posts = FluentCrm\App\Models\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:
```php
// Retrieve all posts that have at least one comment with votes...
$posts = FluentCrm\App\Models\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:
```php
// Retrieve all posts with at least one comment containing words like foo%
$posts = FluentCrm\App\Models\Post::whereHas('comments', function ($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:
```php
$posts = FluentCrm\App\Models\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 allow you to add customized constraints to a relationship constraint, such as checking the content of a comment:
```php
$posts = FluentCrm\App\Models\Post::whereDoesntHave('comments', function ($query) {
    $query->where('content', 'like', 'foo%');
})->get();
```
You may use "dot" notation to execute a query against a nested relationship. For example, the following query will retrieve all posts with comments from authors that are not banned:
```php
$posts = FluentCrm\App\Models\Post::whereDoesntHave('comments.author', function ($query) {
    $query->where('banned', 1);
})->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:
```php
$posts = FluentCrm\App\Models\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:
```php
$posts = FluentCrm\App\Models\Post::withCount(['votes', 'comments' => function ($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:
```php
$posts = FluentCrm\App\Models\Post::withCount([
    'comments',
    'comments as pending_comments_count' => function ($query) {
        $query->where('approved', false);
    }
])->get();
 
echo $posts[0]->comments_count;
 
echo $posts[0]->pending_comments_count;
```


### Eager Loading
When accessing Fluent ORM 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, Fluent ORM 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
<?php
 
namespace FluentCrm\App\Models;
 
use FluentCrm\Framework\Database\Orm\Model;
 
class Book extends Model
{
    /**
     * Get the author that wrote the book.
     */
    public function author()
    {
        return $this->belongsTo('FluentCrm\App\Models\Author');
    }
}
```
Now, let's retrieve all books and their authors:
```php
$books = FluentCrm\App\Models\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:
```php
$books = FluentCrm\App\Models\Book::with('author')->get();
 
foreach ($books as $book) {
    echo $book->author->name;
}
```
For this operation, only two queries will be executed:
```sql
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:
```php
$books = FluentCrm\App\Models\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 Fluent ORM statement:
```php
$books = FluentCrm\App\Models\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, Fluent ORM allows you to specify which columns of the relationship you would like to retrieve:
```php
$users = FluentCrm\App\Models\Book::with('author:id,name')->get();
```

### 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:
```php
$users = FluentCrm\App\Models\User::with(['posts' => function ($query) {
    $query->where('title', 'like', '%first%');
}])->get();
```
In this example, Fluent ORM will only eager load posts where the post's title column contains the word first. Of course, you may call other <a href="/database/query-builder">query builders</a> methods to further customize the eager loading operation:
```php
$users = FluentCrm\App\Models\User::with(['posts' => function ($query) {
    $query->orderBy('created_at', 'desc');
}])->get();
```


## Inserting & Updating Related Models

### The Save Method
Fluent ORM 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:
```php
$comment = new FluentCrm\App\Models\Comment(['message' => 'A new comment.']);
 
$post = FluentCrm\App\Models\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:
```php
$post = new FluentCrm\App\Models\Post::find(1);
 
$post->comments()->saveMany([
    new FluentCrm\App\Models\Comment(['message' => 'A new comment.']),
    new FluentCrm\App\Models\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 Fluent ORM model instance while `create` accepts a plain PHP `array`:
```php
$post = FluentCrm\App\Models\Post::find(1);
 
$comment = $post->comments()->create([
    'message' => 'A new comment.',
]);
```
You may use the `createMany` method to create multiple related models:
```php
$post = FluentCrm\App\Models\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:
```php
$account = FluentCrm\App\Models\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`:
```php
$user->account()->dissociate();
 
$user->save();
```

### Many To Many Relationships

#### Attaching / Detaching
Fluent ORM 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:
```php
$user = FluentCrm\App\Models\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:
```php
$user->roles()->attach($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:
```php
// 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:
```php
$user = FluentCrm\App\Models\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:
```php
$user->roles()->sync([1, 2, 3]);
```
You may also pass additional intermediate table values with the IDs:
```php
$user->roles()->sync([1 => ['expires' => true], 2, 3]);
```
If you do not want to detach existing IDs, you may use the `syncWithoutDetaching` method:
```php
$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:
```php
$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:
```php
FluentCrm\App\Models\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:
```php
$user = FluentCrm\App\Models\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`. Fluent ORM makes it easy. Just add a `touches` property containing the names of the relationships to the child model:
```php
<?php
 
namespace FluentCrm\App\Models;
 
use FluentCrm\Framework\Database\Orm\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('FluentCrm\App\Models\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:
```php
$comment = FluentCrm\App\Models\Comment::find(1);
 
$comment->text = 'Edit to this comment!';
 
$comment->save();
```