# Relationships

# Relationship Fields

In addition to the variety of attributes we've already discussed, Laravel JSON:API has full support for all of Laravel's Eloquent relationships. To add a relationship to a schema, we can simply add it to the schema's fields method.

Our relationship fields take care of querying and hydrating relationships.

To create a relationship, we use the static make method, providing the JSON:API field name as the first argument. For example, if our Post schema had author and tags relationships:

use LaravelJsonApi\Eloquent\Fields\ID;
use LaravelJsonApi\Eloquent\Fields\Relations\BelongsTo;
use LaravelJsonApi\Eloquent\Fields\Relations\HasMany;

/**
 * @inheritDoc
 */
public function fields(): array
{
    return [
        ID::make(),
        // ...attribute fields
        BelongsTo::make('user'),
        HasMany::make('tags'),
    ];
}

# Model Method Names

By default, the field will expect the method for the relationship on the Eloquent model to be the camel-case form of the JSON:API field name. For example, for a relationship field name of blog-author, the expected method on the Eloquent model would be blogAuthor.

To use a different method name than the default, provide the method name as the second argument to the make method:

BelongsTo::make('author', 'blogAuthor');

# URI Name

By default we dasherize the JSON:API field name when it appears in relationship URLs. For example, if the field name was blogAuthor, the links would be:

{
  "links": {
    "self": "http://localhost/api/v1/posts/123/relationships/blog-author",
    "related": "http://localhost/api/v1/posts/123/blog-author"
  }
}

If you wanted to keep blogAuthor as-is, use the retainFieldName method:

BelongsTo::make('blogAuthor')->retainFieldName()

Otherwise, if you want to use a different convention, provide the URI fragment to the withUriFieldName method:

BelongsTo::make('blogAuthor')->withUriFieldName('blog_author')

# Inverse Type

Every relationship must have an inverse resource type. This is the JSON:API resource type that is returned by the relationship.

For relationships that return zero-to-one related resources (known as to-one relations), we assume the inverse type is the dasherized and pluralized form of the Eloquent method name. For example:

BelongsTo::make('blogPost') // assumed 'blog-posts'
BelongsTo::make('author', 'user') // assumed 'users'

For relationships that return zero-to-many related resources (known as to-many relations), we assume the inverse type is the dasherized form of the Eloquent method name. For example:

HasMany::make('postTags') // assumed 'post-tags'
HasMany::make('tags', 'postTags') // assumed 'post-tags'

In either case, to use a different inverse resource type, just call the type() method. For example if our Post schema has an author relationship field, but the inverse type was users:

BelongsTo::make('author')->type('users')

# Eager Loading

By default, all relationship field types are allowed as include paths (opens new window). This is the equivalent of Eloquent's eager loading capability.

If you do not want to allow a relationship field to be an include path, use the cannotEagerLoad method:

BelongsTo::make('author')->cannotEagerLoad()

For more detail, see the Eager Loading chapter.

# Sparse Fields

By default, all relationship field types are allowed as sparse fields (opens new window). If you do not want to allow an relationship to be a sparse field, you should use the notSparseField method:

BelongsTo::make('author')->notSparseField()

# Read-Only Fields

The majority of our relationship fields are writeable, with the exception of the HasOneThrough and HasManyThrough relationships which are always read-only.

For the other relationship fields, there are times when you may want to allow the client to only create or update certain relationships on the resource. You can do this by using the readOnly method, which will prevent the field from being filled

BelongsTo::make('author')->readOnly()

If you need a relationships to only be filled in certain circumstances, pass a closure to the readOnly method. It will receive the current request as the first argument:

BelongsTo::make('author')->readOnly(
    static fn($request) => !$request->user()->isAdmin()
)

If you only want to set the relationship to read only when creating or updating resources, you may use the readOnlyOnCreate or readOnlyOnUpdate methods:

BelongsTo::make('author')->readOnlyOnCreate()
BelongsTo::make('author')->readOnlyOnUpdate()

WARNING

The read-only methods on relationships only affect the relationship when it is being filled as a result of a POST or PATCH request for a resource type. For example, the author field on a posts resource will have its read-only state checked when the client has submitted a request to create or update a posts resource, i.e. a request to POST /api/v1/posts or PATCH /api/v1/posts/123

The read-only methods do not affect changing relationships via relationship end-points: e.g. PATCH /api/v1/posts/123/relationships/author. There is no need for us to check the read-only status in this circumstance because this relationship route should not be registered with the Laravel router if the relationship is read-only.

# Countable Fields

Sometimes a client may want to count the number of related resources for a given relationship without actually loading the related resources. Our to-many fields allow this using our Countable Relationships feature.

# Relationship Serialization

Schemas are used to convert models to JSON:API resource objects. Each relationship you define will appear in the resource JSON. Each relationship is serialized as a JSON:API relationship object (opens new window). These relationship objects must contain at least one of links, data or meta.

By default, relationship objects are serialized with the links member, and will include the self and related links. The data member will only be included if the relationship data has been requested by the client using an Include Path. (opens new window)

To customise the relation serialization, use the serializeUsing method. This receives the JSON:API relation as its first argument:

BelongsTo::make('author')->serializeUsing(
  static fn($relation) => $relation->withoutSelfLink()
)

If you do not want the relationship object to have a self link, use the withoutSelfLink method:

BelongsTo::make('author')->serializeUsing(
  static fn($relation) => $relation->withoutSelfLink()
)

Likewise, if you do not want the relationship object to have a related link, use the withoutRelatedLink method:

BelongsTo::make('author')->serializeUsing(
  static fn($relation) => $relation->withoutRelatedLink()
)

If you want to remove both the self and related links, you can use the withoutLinks method:

BelongsTo::make('author')->serializeUsing(
  static fn($relation) => $relation->withoutLinks()
)

# Showing Data

By default we only show the data member of the relationship if the client has requested it using an include path. This is a sensible default because the whole point of the JSON:API specification is to give the client complete control over what it wants include in the response JSON. If the server made decisions over what is included, then it will increase the size of the response payload when the client may have no intent to use the extra JSON content.

If you must override this, we provide two methods on the relation. Firstly, the showDataIfLoaded method will include the relationship data member if the relation is loaded on the model:

BelongsTo::make('author')->serializeUsing(
  static fn($relation) => $relation->showDataIfLoaded()
)

Secondly we provide the alwaysShowData member to force the data member to be shown. If you are using the alwaysShowData method, you will need to consider adding default eager load paths to your schema to avoid "N+1" database query problems.

BelongsTo::make('author')->serializeUsing(
  static fn($relation) => $relation->alwaysShowData()
)

WARNING

If you use the alwaysShowData method, you must ensure that the relationship is always eager loaded. See the Eager Loading chapter for details.

# Hiding Fields

When serializing relationships to JSON, you may want to omit a field from the JSON. To do this, use the hidden method:

BelongsTo::make('createdBy')->hidden()

To only hide the field in certain circumstances, provide a closure to the hidden method. It will receive the current request as the first argument:

BelongsTo::make('createdBy')->hidden(
  static fn($request) => !$request->user()->isAdmin()
)

Note that if you use JSON:API resources outside of HTTP requests - for example, queued broadcasting - then your closure should handle the $request parameter being null.

TIP

If you have complex logic for determining what relationships should appear in the resource's JSON, you should use our resource classes which give you complete control over the serialization.

# Relationship Types

Laravel JSON:API ships with field types that work with all of the Eloquent relationships. The types are:

JSON:API Type Eloquent Type(s) Writeable
Has One hasOne, morphOne Yes
Has Many hasMany, morphMany Yes
Has One Through hasOneThrough No
Has Many Through hasManyThrough No
Belongs To belongsTo Yes
Belongs To Many belongsToMany, morphToMany, morphedByMany Yes
Morph To morphTo Yes
Morph to Many None Yes

# Has One

The HasOne field corresponds to either a hasOne or morphOne Eloquent relationship. For example, let's assume a User model hasOne Address model. We may add the relationship to our User schema like so:

use LaravelJsonApi\Eloquent\Fields\Relations\HasOne;

HasOne::make('address')

As described above, this will assume the method name on the model is address. If this is not the case, the method name can be provided as the second argument:

HasOne::make('address', 'postalAddress')

The inverse resource type is assumed to be the pluralized and dasherized form of the Eloquent method name. If this is not the case, use the type method:

HasOne::make('address') // assumed 'addresses'
HasOne::make('address')->type('user-addresses')

# Detaching Has-One Models

When modifying this relationship, you will need to consider how you want to handle a model being detached from the relationship. For example, if a User model already had one Address and the client changes the relationship to null or a different Address, how should the existing Address model be detached?

The default detach behaviour is to set the relationship columns on the Address model to null. I.e. the Address model is retained and detached from the User model.

In some cases, you might actually want the Address model to be deleted if it is detached from the relationship. You can configure this behaviour using the deleteDetachedModel() or forceDeleteDetachedModel() methods on the HasOne field. For example:

HasOne::make('address')->deleteDetachedModel()
// or
HasOne::make('address')->forceDeleteDetachedModel()

# Has Many

The HasMany field corresponds to a hasMany or a morphMany Eloquent relationship. For example, let's assume that our Video model hasMany Comment models. We may add the relationship to our Video schema like so:

use LaravelJsonApi\Eloquent\Fields\Relations\HasMany;

HasMany::make('comments')

As described above, this will assume the method name on the model is comments. If this is not the case, the method name can be provided as the second argument:

HasMany::make('comments', 'userComments')

The inverse resource type is assumed to be the dasherized form of the Eloquent method name. If this is not the case, use the type method:

HasMany::make('comments') // assumed 'comments'
HasMany::make('comments')->type('video-comments')

# Detaching Has-Many Models

When modifying this relationship, you will need to consider how you want to handle models that are detached from the relationship. For example, when updating the Video model's comments relationship, Comment models may be detached (removed).

The default detach behaviour is to set the relationship columns on the Comment model to null. I.e. each Comment model removed from the relationship is retained and detached from the Video model.

In some cases, you might actually want Comment models to be deleted when they are detached from the relationship. You can configure this behaviour using the deleteDetachedModels() or forceDeleteDetachedModels() methods on the HasMany field. For example:

HasMany::make('comments')->deleteDetachedModels()
// or
HasMany::make('comments')->forceDeleteDetachedModels()

# Has One Through

The HasOneThrough field corresponds to a hasOneThrough Eloquent relationship. For example, let's assume a Mechanic model has one Car, and each Car may have one Owner. While the Mechanic and the Owner has no direct connection, the Mechanic can access the Owner through the Car itself.

You can add this relationship to your Mechanic schema as follows:

use LaravelJsonApi\Eloquent\Fields\Relations\HasOneThrough;

HasOneThrough::make('owner')

As described above, this will assume the method name on the model is owner. If this is not the case, the method name can be provided as the second argument:

HasOneThrough::make('owner', 'carOwner');

The inverse resource type is assumed to be the pluralized and dasherized form of the Eloquent method name. If this is not the case, use the type method:

HasOneThrough::make('owner') // assumed 'owners'
HasOneThrough::make('owner')->type('car-owners')

WARNING

The HasOneThrough field cannot be hydrated (filled). This is because the intermediary resource should be created or updated instead.

Using our example, a JSON:API client can create or update a cars resource, and its related owner and mechanic. That would change the mechanics has-one-through owner relation.

# Has Many Through

The HasManyThrough field corresponds to a hasManyThrough Eloquent relationship. 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.

You can add this relationship to your Country schema as follows:

use LaravelJsonApi\Eloquent\Fields\Relations\HasManyThrough;

HasManyThrough::make('posts')

As described above, this will assume the method name on the model is posts. If this is not the case, the method name can be provided as the second argument:

HasManyThrough::make('posts', 'blogPosts')

The inverse resource type is assumed to be the dasherized form of the Eloquent method name. If this is not the case, use the type method:

HasManyThrough::make('posts') // assumed 'posts'
HasManyThrough::make('posts')->type('blog-posts')

WARNING

The HasManyThrough field cannot be hydrated (filled). This is because the intermediary resource should be created or updated instead.

Using our example, the contents of the Country's posts relationship is generated by the User models that are linked to Post models. Therefore a JSON:API client would create or update a posts resource, and/or change the country linked to a users resource, to amend the country's posts relationship.

# Belongs To

The BelongsTo field corresponds to a belongsTo Eloquent relationship. For example. let's assume a Post model belongsTo a User model. We may add the relationship to our Post schema like so:

use LaravelJsonApi\Eloquent\Fields\Relations\BelongsTo;

BelongsTo::make('user')

As described above, this will assume the method name on the model is user. If this is not the case, the method name can be provided as the second argument:

BelongsTo::make('author', 'user')

The inverse resource type is assumed to be the pluralized and dasherized form of the Eloquent method name. If this is not the case, use the type method:

BelongsTo::make('author', 'user') // assumed 'users'
BelongsTo::make('author')->type('users')

# Belongs To Many

The BelongsToMany field corresponds to a belongsToMany, morphToMany or morphedByMany Eloquent relationship. For example, let's assume a User model belongsToMany Role models. We may add the relationship to our User schema like so:

use LaravelJsonApi\Eloquent\Fields\Relations\BelongsToMany;

BelongsToMany::make('roles');

As described above, this will assume the method name on the model is roles. If this is not the case, the method name can be provided as the second argument:

BelongsToMany::make('roles', 'accessRoles')

The inverse resource type is assumed to be the dasherized form of the Eloquent method name. If this is not the case, use the type method:

BelongsToMany::make('roles') // assumed 'roles'
BelongsToMany::make('roles')->type('access-roles')

# Pivot Table

If your BelongsToMany relationship interacts with additional pivot columns that are stored on the intermediate table of the relationship, you may also attach these to the relationship.

TIP

The JSON:API specification does not allow attributes to be sent with relationship identifiers. It is therefore important to understand that the follow examples only allow us to add server-calculated values to a pivot table.

If you need the client to provide values for a pivot table, then you should use a pivot model for the intermediary table, and add that model to your API as its own resource type. So in the following example, we would have a RoleUser model for the intermediary role_user table, and have a JSON:API resource called role-users.

For example, let's assume our User model belongsToMany Role models. On our role_user intermediate table, let's imagine that we have an approved column that contains a flag as to whether an administrator created the relationship between the User and the Role. We can store this information by providing a callback to the fields method on the relationship:

BelongsToMany::make('roles')->fields(static fn($parent, $related) => [
  'approved' => \Auth::user()->admin,
]);

TIP

The callback receives two arguments: the parent of the relationship, and the models that are being attached. In this example, the parent would be the User model, and the related models would be Role models.

To provide values that require no calculation, pass an array to the fields method:

BelongsToMany::make('roles')->fields(['approved' => false]);

Of course we could also add this pivot data on the inverse of the relationship. So, if we define the BelongsToMany field on the User schema, we would also define its inverse on the Role schema:

BelongsToMany::make('users')->fields(static fn() => [
  'approved' => \Auth::user()->admin,
]);

Since defining the field on both ends of the relationship can cause some code duplication, we allow you to pass an invokable object to the fields method:

BelongsToMany::make('roles')->fields(new ApprovedPivot())

In this example, the ApprovedPivot could be a simple, invokable class that returns the array of pivot fields:

namespace App\JsonApi\Pivots;

use Illuminate\Support\Facades\Auth;
use function boolval;
use function optional;

class ApprovedPivot
{

    /**
     * Get the pivot attributes.
     *
     * @param $parent
     * @param $related
     * @return array
     */
    public function __invoke($parent, $related): array
    {
        return [
            'approved' => boolval(optional(Auth::user())->admin),
        ];
    }

}

# Morph To

The MorphTo field corresponds to a morphTo Eloquent relationship. For example, let's assume a Comment model has a polymorphic relationship with both the Post and Video models. We may add the relationship to our Comment schema like so:

use LaravelJsonApi\Eloquent\Fields\Relations\MorphTo;

MorphTo::make('commentable')->types('posts', 'videos')

As you can see from the above example, the types method is used to instruct the MorphTo field what its inverse JSON:API resource types are.

As described above, this will assume the method name on the model is commentable. If this is not the case, the method name can be provided as the second argument:

MorphTo::make('commentable', 'items')

# Morph To Many

The JSON:API MorphToMany field helps you construct polymorphic to-many relationships. It's important to note that there is not an equivalent relationship type in Eloquent. (The Eloquent morphToMany relationship type is handled by the BelongsToMany JSON:API field.)

Adding polymorphic to-many relations involves a number of complexities and limitations. As such, there is a chapter covering exactly this topic, where you can find instructions on how to add this relationship to your schema.

Last Updated: 4/22/2021, 4:56:42 PM