C＃类设计问题以使其可测试

Question

I've a scenario which is explained with the help of the following code

namespace SyncDemo
{
    public interface IProcessorA
    {
        void FunctionA(int a);
        void FunctionB(string b);
    }
    public interface IProcessorB
    {
        void FunctionA(int a);
        void FunctionB();
    }
    public interface IRepositoryA
    {
        void Add();
        void Delete();
    }
    public interface IRepositoryB
    {
        void Add();
        Void Delete();
    }

    public class ProcessorA : IProcessorA
    {
        private readonly IRepositoryA _repositoryA;

        public ProcessorA(IRepositoryA repositoryA)
        {
            _repositoryA = repositoryA;
        }

        public void FunctionA(int a)
        {
            //business logic work
            _repositoryA.Add();
        }

        public void FunctionB(string b)
        {
            _repositoryA.Delete();
        }
    }

    public class ProcessorB : IProcessorB
    {
        private readonly IRepositoryA _repositoryA;
        private readonly IRepositoryB _repositoryB;

        public ProcessorB(IRepositoryA repositoryA, IRepositoryB repositoryB)
        {
            _repositoryA = repositoryA;
            _repositoryB = repositoryB;
        }

        public void FunctionA(int a)
        {
            //do the same business logic work as in FunctionA in Class ProcessorA
            _repositoryA.Add();
        }

        public void FunctionB()
        {
            _repositoryB.Delete();
        }
    }

    public class RepositoryA : IRepositoryA
    {
        //this repository is responsible to talk with 'A' data source
        public void Add()
        {
            throw new NotImplementedException();
        }

        public void Delete()
        {
            throw new NotImplementedException();
        }
    }

    public class RepositoryB : IRepositoryB
    {
        //this repository is reponsible to talk with 'B' data source
        public void Add()
        {
            throw new NotImplementedException();
        }

        public void Delete()
        {
            throw new NotImplementedException();
        }
    }
}

There is a common functionality wherein i have to apply the same business logic in both the processors before calling the repository. Also, there are other methods in ProcessorA and ProcessorB which call the repository directly as there is no business logic to be applied.

My dilemma is where to put the common business logic functionality code. Should i create a separate class with that common functionality in a static method or shall i create a separate class which takes the responsibility of talking with the RepositoryA and do the business logic as well?

Any ideas and help is appreciated. Thanks in advance.

Suyog.

Answer 1

If you are following Object-Oriented Design Guidelines like the SOLID Principles and other principles like DRY etc. you should be aware of the Single Responsibility Principle (SRP) which states that a class should have only one responsibility (purpose) and therefore only one reason to change.

Now I don't know the concrete context you are working in but according to the SRP you have to decide if that responsibility of common functionality you are talking about belongs in a separate class or not. There are also several Design Patterns like the eg the Template Method Pattern or maybe the Strategy Pattern that you can use to structure your code in a way that it is following the Don't-Repeat-Yourself Principle (DRY).

For myself, I would first check if I can eliminate one of the repository interfaces and one of the processor interface: they seem rather similar, eg the IProcessorB interface just has an additional string parameter in its FunctionB that separates it from IProcessorA . Can you avoid this (maybe by injecting the string to the constructor of the concrete class that implements this interface) and thus form a common interface that is implemented by several classes? This would for example allow you to introduce the Decorator Pattern into your code.

Anyway these are just guesses by me as I don't know the concrete code you are working on. If you have any further questions, please feel free to ask.