How to get a single field from a Laravel whenLoaded resource

Question

I am using a Laravel Resource to return my object. The object has optional relationships. My Resource code so far is below and is working as expected:

public function toArray(Request $request): array
{
    return [
        'id'                 => (string) $this->id,
        'attributes'         => [
            'name'             => $this->name,
            'status_id'        => $this->status_id,
            'created_at'       => $this->created_at,
            'updated_at'       => $this->updated_at,
        ],
        'relationships' => [
            'status'        => $this->whenLoaded('status'),
        ]
    ];
}

But I would like for the "status" relationship to only include one field from the model - the name. I thought just appending ->name would work. i.e. 'status' => $this->whenLoaded('status')->name,

This does work when the relationship is loaded, but generates an error when the relationship does not exist.

Is there any way to use whenLoaded and show only one field?

Answer 1

I think I have found the answer.

public function toArray(Request $request): array
{
    return [
        'id'                 => (string) $this->id,
        'attributes'         => [
            'name'             => $this->name,
            'status_id'        => $this->status_id,
            'created_at'       => $this->created_at,
            'updated_at'       => $this->updated_at,
        ],
        'relationships' => [
            'status' => $this->when(
                $this->resource->relationLoaded('status'), function ()
                {
                    return $this->resource->status->name;
                }),
        ]
    ];
}

Answer 2

You can use the optional helper function provided by Laravel. The optional function accepts the object you want to work with and returns a new, nullable object. This way, you can safely access the "name" attribute even if the relationship is not loaded.

public function toArray(Request $request): array
{
    return [
        'id'          => (string) $this->id,
        'attributes'  => [
            'name'      => $this->name,
            'status_id' => $this->status_id,
            'created_at' => $this->created_at,
            'updated_at' => $this->updated_at,
        ],
        'relationships' => [
            'status' => optional($this->whenLoaded('status'))->only('name'),
        ],
    ];
}

Answer 3

You can add the value you wish to return from whenLoaded via the 2nd param, with the 3rd param being a default value to return.

'status' => $this->whenLoaded('status', 'the value I wish to return', 'a default value if relationship is not loaded');

There is an issue though if you want to return a field from the relationship:

'status' => $this->whenLoaded('status', $this->status->name);

The above looks like it will work. But by calling $this->status->name, and say you have no eager loaded the relationship, it will load the relationship and whenLoaded will have no effect.

A solution would be to use a callback:

'status' => $this->whenLoaded('status', fn () => $this->status->name);