Resolving abstract class' dependencies via dependency injection in Laravel - php

Question

I encountered this issue using the repository pattern. Currently I use an interface, and a custom class to achieve it, then type-hint it into the controller's construct and because of Laravel, it will solve the repositories' dependencies automatically and recursively.
I also do this in a service provider:
$this->app->bind(path/to/repoInterface,path/to/implementationClass)
However, because of the way I coded these repositories, in order to avoid code duplication, I created an abstract class that has a common method to all these repositories. This class is as follows:
abstract class CommonRepo{
public function __construct(SomeModelClass model){}
public function commonMethod(){//Code here}
And my repositories have the following structure:
public class ExampleRepository extends CommonRepo implements ExampleRepositoryI{
public function __construct(){
parent::__construct();
}
}
Laravel doesn't like this, so its giving this error:
Argument 1 passed to path/to/repo/CommonRepo::__construct() must be an instance of path/to/model/SomeModelClass, none given, called in...
So, obviously is not resolving the dependency of the class CommonRepo, but it does resolve the dependencies on the normal repositories.
I'd like, if it's possible, to use type-hinting (the Laravel way) without having to do anything related to the new operator
How can I, then, resolve that class's dependencies ?
PD: Using Laravel 5.2

Answer 1

Parent constructor is called like normal function without touching dependency resolver so you should do one of two possibilities:
public class ExampleRepository extends CommonRepo implements ExampleRepositoryI
{
public function __construct(SomeModelClass $model){
parent::__construct($model);
}
}
or
public class ExampleRepository extends CommonRepo implements ExampleRepositoryI
{
public function __construct(){
parent::__construct(App::make(SomeModelClass::class));
}
}

Answer 2

nice question. I did some tinkering, though I don't know if this is what you're looking for. But you can dynamically create an instance of Eloquent model required by your repository class.
Let's say you have your User model class stored in app\Models\User.php:
<?php
namespace App\Models;
use Illuminate\Database\Eloquent\Model;
class User extends Model
{
//
}
You then create a base abstract class for all of your repository classes: app\Repositories\BaseRepository.php. This is where you place all common functionalities for your repository classes. But rather than injecting the Eloquent instance through the constructor, you may add a method named getModel() to dynamically create an instance of Eloquent model for your repository.
<?php
namespace App\Repositories;
use ReflectionClass;
use RuntimeException;
use Illuminate\Support\Str;
abstract class BaseRepository
{
protected $modelNamespace = 'App\\Models\\';
public function getById($id)
{
return $this->getModel()->find($id);
}
public function getModel()
{
$repositoryClassName = (new ReflectionClass($this))->getShortName();
$modelRepositoryClassName = $this->modelNamespace . Str::replaceLast('Repository', '', $repositoryClassName);
if (! class_exists($modelRepositoryClassName)) {
throw new RuntimeException("Class {$modelRepositoryClassName} does not exists.");
}
return new $modelRepositoryClassName;
}
}
Now let's say you want to create a repository for your User model, and this user's repository must implement the following interface: app\Repositories\UserRepositoryInterface.php
<?php
namespace App\Repositories;
interface UserRepositoryInterface
{
public function getByEmail($email);
}
You create app\Repositories\UserRepository.php class and simply extend it from the BaseRepository class. Also don't forget to implement all specific implementations defined on UserRepositoryInterface.
<?php
namespace App\Repositories;
use App\Repositories\BaseRepository;
use App\Repositories\UserRepositoryInterface;
class UserRepository extends BaseRepository implements UserRepositoryInterface
{
public function getByEmail($email)
{
return $this->getModel()->where('email', $email)->firstOrFail();
}
}
This way you can bind the UserRepositoryInterface to it's implementation like so:
$this->app->bind(\App\Repositories\UserRepositoryInterface::class, \App\Repositories\UserRepository::class);
Finally you can freely inject the UserRepositoryInterface to a controller's constructor or methods. You can also resolve it via service container like this:
$userRepository = App::make(App\Repositories\UserRepositoryInterface::class);
$userRepository->getByEmail('john#example.com');
Of course there's a catch to this approach. The repository class should be started with the associated model, so the InvoiceRepository.php is dedicated for Invoice.php model class.
Hope this help!

Answer 3

This might help. You can listen in for when an object resolves and set attributes.
$this->app->resolving(CommonRepo::class, function ($object, $app) {
// Called when container resolves object of any type...
$object->commonObject = app(CommonObject::class);
});
Docs: https://laravel.com/docs/5.4/container#container-events