Beware of Circular Dependency Issues in PHP/Laravel — See Symptoms and Solution

What is Circular Dependency?

A circular dependency occurs when two or more classes or components directly or indirectly depend on each other, forming a cycle. This applies to most programming languages and is not unique to PHP/Laravel.

For example:

• Class UserService depends on Class CarService.
• Class CarService depends on Class UserService.

This creates a loop, where each class waits for the other to be initialized, causing errors such as infinite recursion, stack overflow, or failure to resolve the dependencies.

Example:

<?php 

class UserService {
    public function __construct(CarService $car) {}
}

class CarService {
    public function __construct(UserService $user) {}
}

In this case, Laravel’s dependency injection container would struggle to instantiate either UserService or CarService because each requires the other to be instantiated first.

Symptoms

• Artisan Commands Fail:
  If all Artisan commands fail without any output or warning — for example, running php artisan list returns nothing—this is a sign of a deeper issue.
• Composer Install Stuck at php artisan package:discover - ansi:
  This issue is related to the failure of Artisan commands. The Composer installation may get stuck at this stage because it attempts to autoload classes that have circular dependency issues.
• PC Making Noise and Slowing Down:
  While running your script, you may notice that your PC’s RAM usage is high and CPU utilization spikes. This can cause your PC’s fan to turn on and run loudly, indicating that your machine is struggling to keep up.

Solutions:

• Refactor the Design: Break the cycle by refactoring the design, ensuring that dependencies do not rely on each other.
• Use a Factory or Service Locator: In cases where circular dependencies are unavoidable, you can use a factory or a service locator to inject the dependencies manually at a later stage.
• Defer Injection: One class might only need the other later in its lifecycle, so inject the dependency lazily instead of in the constructor.

Solution Examples: Problem Scenario (Circular Dependency)

Let’s say you have two classes, ClassA and ClassB, that depend on each other, causing a circular dependency issue:

class ClassA {
    protected $classB;

    public function __construct(ClassB $classB) {
        $this->classB = $classB;
    }
}

class ClassB {
    protected $classA;

    public function __construct(ClassA $classA) {
        $this->classA = $classA;
    }
}

Solution: Using a Factory to Break the Circular Dependency

Instead of injecting ClassB into ClassA directly via the constructor, we can use a factory method that delays the injection until after the object is constructed, breaking the circular dependency.

Step 1: Create a Factory for ClassA and ClassB

class ClassAFactory {
    public static function create() {
        // Create ClassA without injecting ClassB immediately
        $classA = new ClassA();
        
        // Inject ClassB manually after both instances are created
        $classB = new ClassB($classA);
        $classA->setClassB($classB);
        
        return $classA;
    }
}

Step 2: Modify Classes to Use Setter Injection

class ClassA {
    protected $classB;

    public function setClassB(ClassB $classB) {
        $this->classB = $classB;
    }

    public function doSomething() {
        // Logic involving $classB
    }
}

class ClassB {
    protected $classA;

    public function __construct(ClassA $classA) {
        $this->classA = $classA;
    }

    public function doSomething() {
        // Logic involving $classA
    }
}

Step 3: Use the Factory to Create the Objects

$classA = ClassAFactory::create();
$classA->doSomething();