[9.x] Add whenHas to JsonResource

[michaelnabil230]

This PR adds a whenHas method to the JSON resource class giving us the ability to conditionally include attributes in a response when an attribute has in the model.

In some time to need to make many resources for return data to API because we do need to return for example in the function index only id and name for the user. But in the show function, you need all data for the user.

To fix this problem need to make many resources for resolving it.

And I think all developers need this feature

Note: I make some clear and enhancement whenCounted to whenHas function

Before:

class UserController
{
    public function index()
    {
        $users = User::select(['id', 'name'])->get();

        return UserResource::collection($users);
    }

    public function show(User $user)
    {
        return SingleUserResource::make($user);
    }
}

class UserResource extends Resource
{
    public function toArray($request)
    {
        return [
            'id' => $this->id,
            'name' => $this->name,
        ];
    }
}

class SingleUserResource extends Resource
{
    public function toArray($request)
    {
        return [
            'id' => $this->id,
            'name' => $this->name,
            'email' => $this->email,
        ];
    }
}

Now with magic function with the same Resource:

class UserController
{
    public function index()
    {
        $users = User::select(['id', 'name'])->get();

        return UserResource::collection($users);
    }

    public function show(User $user)
    {
        return UserResource::make($user);
    }
}

class UserResource extends Resource
{
    public function toArray($request)
    {
        return [
            'id' => $this->id,
            'name' => $this->name,
            'email' => $this->whenHas('email'),
        ];
    }
}

[taylorotwell]

Why can you not just use whenNotNull($this->email) in your example?

[michaelnabil230]

@taylorotwell At some times, the default value is null for example email_verified_at
Not can use the whenNotNull($this->email_verified_at) in this case but if use whenHas($this->email_verified_at) return null if the attribute in resource attributes

[michaelnabil230]

If you select email_verified_at from the User model and the default value is null to return a null in the user response does not return the MissingValue class. And on the other hand when using whenNotNull return the MissingValue class.

[MasterRO94]

As for me naming is inconvenient to other Laravel classes. It would be better name it whenExists or whenPresent