BusinessManagement | web development Business Management project | Business library

I think you're right to worry about avoiding coupling here – I would consider your example to be bad practice. But let's unpack, and show a way that we can achieve the same behaviour with a contract between the classes that is more comprehensible, predictable and maintainable.

A business has many employees, it knows who it employs - so it makes sense for it to own a collection of references to Employee objects. An employee (for the sake of simplicity) works for one business, so it makes sense for an Employee to contain a reference to a Business object. These references do not necessarily couple the classes together in a negative sense, so long as the contracts between them are clearly in public methods on each object whose invocation is controlled by that class, and whose business logic is the concern of that class.

A business fires an employee, and an employee also needs to know that they are fired. If I was going to do this, I would put the Fire(Employee e) method on the Business class - inside this method, I would most likely want to call e.GetFired() then remove the employee from the collection of employees. Then, Employee.GetFired() would set the Employee's own Business property to null.

This can work in both directions while maintaining the separation between these classes. An employee, presumably, can quit their job - Thus, Employee.Quit() can call Business.EmployeeHasQuit(Employee e), passing itself in as a reference - allowing the Business instance to take responsibility itself for removing the Employee instance from the collection.

Your example is an example of coupling because the Employee class' GetFired() method used it's reference to a Business object to access a public collection and delete itself. It would also be coupling if the Business.Fire(Employee e) method set e.Business = null. It's a reasonable rule of thumb that classes should not directly modify the members of other classes; by letting each class manage its own state, you can implement behaviours to ensure things are always in a valid state, and to trigger other necessary behaviours (e.g. we want to make sure that when an Employee quits, their security pass is revoked, and this would happen inside EmployeeHasQuit() – if the employee just deleted itself from the Business' collection, this wouldn't be the case. A business might also want the opportunity to put an employee who has quit or been fired into a formerEmployees collection, to keep track of them later.

Hopefully this serves as an easily digestible example of the ways in which objects can communicate with each other while maintaining full responsibility for their own states and behaviours!

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