Laravel5 dependency injection on Model - laravel-5

Question

I have an Eloquent Model called Surface which is dependent on a ZipCodeRepository object:
class Surface extends Model{
public function __construct(ZipCodeRepositoryInterface $zipCode){...}
and an Address object that hasMany surfaces.
class Address extends Model{
public surfaces() { return $this->hasMany('App/Surface'); }
}
My issue is when I call $address->surfaces I get the following error:
Argument 1 passed to App\Surface::__construct() must be an instance of App\Repositories\ZipCodeRepositoryInterface, none given
I thought the IoC would automatically inject that.

Answer 1

Thanks to #svmm for referencing the question mentioned in the comments. I found that you cannot use dependency injection on Models because you would have to change the signature on the constructor which doesn't work with the Eloquent framework.
What I did as an intermediate step, while refactoring the code, is use App::make in the constructor to create the object, such as:
class Surface extends Model{
public function __construct()
{
$this->zipCode = App::make('App\Repositories\ZipCodeRepositoryInterface');
}
That way the IoC will still grab the implemented repository. I am only doing this until I can pull the functions into the repository to remove the dependency.

Answer 2

In Laravel 5.7 you can use the global resolve(...) method. I don't think the global App is defined in more recent version of Laravel.
$myService = resolve(ServiceName::class);
Resolving in Laravel docs

Answer 3

However it might not be a good practice to inject services into your models either by constructor or method injection, think about designing the system in such a way that you do not need to do that and instead maybe inject the model into a service.
Let's see an example(just a dummy example in order to get to the point!).
Say we have Basket and Order models, and we want to add orders to basket
And we have a discount service that calculates discount based on orders
Every time user adds an order to basket we need to calculate new discount and set it on basket
one approach is:
class OrderController
{
function store(User $user, Order $order)
{
$basket = $user->getBasket();
$basket->addOrder($order);
}
}
class Basket
{
private $discountService;
public function __construct(DiscountService $discountService)
{
$this->discountService = $discountService;
}
function addOrder(Order $order)
{
$this->orders[] = $order;
$discount = $this->discountService->calculateFor($this->orders);
$this->discount = $discount;
}
}
class DiscountService
{
function calculateFor(array $orders) {
// code for calculating discount;
return $discount;
}
}
In this approach we injected discount service into Basket model
Another better approach would be like this:
class OrderController
{
private $discountService;
public function __construct(DiscountService $discountService)
{
$this->discountService = $discountService;
}
function store(User $user, Order $order)
{
$basket = $user->getBasket();
$basket->addOrder($order);
$this->discountService->setDiscount($basket);
}
}
class Basket
{
function addOrder(Order $order)
{
$this->orders[] = $order;
}
function getOrders()
{
return $this->orders;
}
function setDiscount(int $discount)
{
$this->discount = $discount;
}
}
class DiscountService
{
function setDiscount(Basket $basket) {
$discount = $this->calculateFor($basket->getOrders());
$basket->setDiscount($discount);
}
private function calculateFor(array $orders)
{
// code for calculating discount
return $discount;
}
}
In the first approach basket is making the decision about having discount, but this is not basket's concern
In the first approach basket depends on discount service, but in real world you don't need a discount service to have a basket