PHP - Service layer class instantiation causing infinite loop - php

Question

I have service layer classes which performs the business logic.
I have a class say UserService which performs user role related service like checking if user is admin, user has access to project, user has particular role or not, etc. And there is a another class say ProjectService which deals with project related things like getting project members, project details, etc.
UserService
$projectService; //class variable
hasProjectAccess(){
{
...
projectMember = projectService->getProjectMembers();
...
}
isUserAdmin(){
return true|false; //just an example
}
ProjectService
$userService; //class variable
getProjectMembers(){
{
...
perform some logic to create array of members
...
if(userService.isUserAdmin())
.. perform some other logic
...
}
I am using Slim 3, where I use it's Container class to instantiate and inject all dependencies.
Now when I try to instantiate UserService class I have to instantiate the ProjectService class inside it (using setters method), which in turn has to instantiate UserService class .... and so on... which creates an infinite loop (cyclic dependency).
I am trying to achieve something like in Java/Spring, where you have different services which you need in your class and they wired into it using Spring so you do not have to worry about the cyclic dependency.
I am not much familiar with PHP except the basics.
Let me know if more information is needed.

Answer 1

Pimple which is used as dependency container in Slim3, isn't that strong as Spring in Java f.ex. it is only a simple container, which just has the basic functionallity.
So when just using the pimple functions you need to initialize your objects which have a cyclic dependency by yourself:
class A {
private $b;
public function __construct(B $b) { $this->b = $b; }
}
class B {
private $a;
public function setA(A $a) { $this->a = $a; }
}
$container = new \Slim\Container;
$b = new B;
$a = new A($b);
$b->setA($a);
$container['A'] = function($c) use ($a) {
return $a;
};
$container['B'] = function($c) use ($b) {
return $b;
};
$aFromContainer = $container['A'];
I've made some small changes to the slim container that it will be possible to automate this process (althrough this work, I dont know how well it does in larger projects).
class MyContainer extends \Slim\Container
implements \Interop\Container\ContainerInterface {
private $resolveStack = [];
private $resolveLater = [];
/**
* #see \Pimple\Container::offsetSet()
*
* Additionally define objects which will be later set with a method.
*/
public function resolveLater(string $id, callable $value, array $later) {
$this[$id] = $value;
foreach($later as $item) {
if(!isset($this->resolveLater[$item])) $this->resolveLater[$item] = [];
$this->resolveLater[$item][] = $id;
}
}
/**
* #see \Pimple\Container::offsetGet()
*
* Additionally set objects which were previously defined in #resolveLater.
*/
public function offsetGet($id) {
if(isset($this->resolveStack[$id])) { return $this->resolveStack[$id]; }
$this->resolveStack[$id] = parent::offsetGet($id);
if(isset($this->resolveLater[$id])) {
foreach($this->resolveLater[$id] as $item) {
$this[$item]->{'set' . $id}($this->resolveStack[$id]);
}
}
return array_pop($this->resolveStack);
}
}
Example for the above:
class A {
public function setB(B $b) { $this->b = $b; }
public function setC(C $c) { $this->c = $c; }
}
class B {
public function setA(A $a) { $this->a = $a; }
public function setC(C $c) { $this->c = $c; }
}
class C {
public function setA(A $a) { $this->a = $a; }
public function setB(B $b) { $this->b = $b; }
}
$container = new MyContainer;
$container->resolveLater('A', function($container) {
return new A;
}, ['B', 'C']);
$container->resolveLater('B', function($container) {
return new B;
}, ['A', 'C']);
$container->resolveLater('C', function($container) {
return new C;
}, ['A','B']);
$a = $container['C'];
var_dump($a);
This would output something like this:
object(C)[20]
public 'b' =>
object(B)[22]
public 'a' =>
object(A)[21]
public 'b' =>
&object(B)[22]
public 'c' =>
&object(C)[20]
public 'c' =>
&object(C)[20]
public 'a' =>
object(A)[21]
public 'b' =>
object(B)[22]
public 'a' =>
&object(A)[21]
public 'c' =>
&object(C)[20]
public 'c' =>
&object(C)[20]