Question

I am working on a class library using C#. I have designed 3 main classes to help model our data. They are designed such that class A contains a list of class B instances, and class B contains a reference to a class C instance, ie:

public class Policy
{
    public List < PolicyTerm > myTerms;
    person Customer;
    string PolicyNumber;
}

public class PolicyTerm
{
     public Billing myBill;
     Datetime effectivedate;
     List < Activities > termActivities;
     public doAction()
     {
          use value from Policy, like PolicyNumber;
     }

}

public class Billing
{
    float remainingBalance;
    Datetime nextDueDate;
    public void doSomething()
    {
         reference value from PolicyTerm, such as effective date;
         use value from Policy, such as PolicyNumber;
    }
}

The problem I have is when I try to use a method within PolicyTerm or Billing that needs data from the containing class. In the example above, this would be the method “doSomething” trying to use a value from PolicyTerm, like the effective date for the term in requesting or saving data to our database.

I am wondering if I have the correct design for my classes because of this scenario. Should I just add a reference to the “parent” class within the child classes, in order to make the parent’s data available? Or do I need to rethink the overall structure and design of the code?

I feel like the class design works well for modeling the data and our business rules, but it does create a few limitations like the above situation. I liked the separation of the PolicyTerm and Billing for the ability to allow that code to be modified and tested independently. Also, I feel like it keeps each section smaller and simpler.

Any advice that can be provided would be much appreciated.

Update: Code block was updated to provide more details on the code in question.

Answer 1

If doSomething() always needs the reference to the C object’s parent, you should indeed put this reference into C where you can ensure that it refers to the correct B instance. OTOH if that reference is not always the parent, but still it is always going to refer to the same B instance, it still suggests turning it into a member of C. OTOH if doSomething() can be called with varying references, that reference should be kept as a method parameter.

It is not bad per se to put a reference from child to parent, or to have a mutual dependency between two classes – it depends on the context. The consequence of this is that the two classes can not be used separately, so in fact they form a component. This may or may not be acceptable for you.

Components in general can consist of multiple classes – a collection with its items and iterator(s) is in fact a typical example. However, it is advisable to express the logical dependency between these classes on the physical level as well, e.g. by making one class an inner class of the other, or making both classes inner classes in a third class.