Place a method in which class

Question

I have a question that's more of a best practice rather that an actual problem.

Supposed I'm building a projects app and each project would have multiple tasks that need to be completed.

So the projects class:

class Project {
    public $id;
    public $name;

    // Get tasks of this project
    public function getTasks() {
            // some logic to get tasks of this project
    }

    // Should a method for adding task go here
    public function addTask() {
           // some logic going here
    }
}

And the tasks class:

class Task {
     public $id;
     public $name;

     // Should a method for adding task go here
     public function add_task($project_id) {
          // The task class here needs to know the project_id
          // to continue with the logic
     }
}

As you can tell, any task always belongs to a certain project.

Adding a task should be considered a method for tasks or because any task always belongs to a project, it should part of the project class?? Is there a more correct one? So a task is a task and at the same time it's owned by a project

Answer 1

Single Responsibility Principle

A class should have one and only one reason to change, meaning that a class should have only one job.

If Project class's responsibility is to manage Tasks, addTask should be a Project method.

Consider the possibility of adding addTask method to Tasks. This would violate the Single Responsibility for the Tasks class. Task would then represent a task, plus it would then have the responsibility of adding itself to some collection of tasks.