Question

I am just starting in DDD and have a question regarding interfaces of objects and repositories. Suppose I have the following objects

public interface IPerson { ... }

public class Student 
{
    double gpa;
    ...
}

public class Teacher
{
    double salary; ...
}

then I also have two repositories such as

public class StudentRepository :IRepository { public void Save(Student) }

public class TeacherRepository :IRepository { public void Save(Teacher) }

My question is, suppose I have a list of IPerson objects called persons, is there a way where I can just do something like repository.Save(persons) ? Without having to use reflection to figure out what type the IPerson actually is.

I currently have another class

PersonRepository :IRepository 
{
     public void Save(IPerson person)
     {
          if(Person is Student)
          {
               new StudentRepository.Save(person as Student);
          }
          else if(Person is Teacher)
          { ....}
      }
}

Then I can call personRepository.Save(persons);
However this doesnt feel like an optimal way to structure things. How can I improve this design?

Thanks

EDIT:

What I’m looking for is, say I receive an IPerson object called person. I do not necessarily know what implementation it is, I just want to call repository.Save(person) and have it call the correct repository. Is there a way to do this without using some sort of switch statement with reflection?

Answer 1

Consider using generic repository

class Repository<T> :IRepository<T>
{
     public void Save(T entity)
     {
         ...
     }
}

Usage

IRepository<Student> repo1 = new Repository<Student>();
repo1.Save(new Student());

IRepository<Teacher> repo2 = new Repository<Teacher>();
repo2.Save(new Teacher());

---

Next you can use IoC container and DI just to pass repositories around instead of creating them

At the top level, say in the main method or global.asax

IRepository<Student> studentRepo = IoC.Current.Resolve<IRepository<Student>>();

Later in a class that needs to save data, pass IRepository<Student> studentRepo into constructor

class Foo
{
    private IRepository<Student> repo

    Foo(IRepository<Student> repo)
    {
        this.repo = repo;
    }

    public void Save(Student s)
    {
        repo.Save(s);
    }
}

EDIT

You can move a save operation to the IPerson<T>

class Person<T> : IPerson<T>
{
    private IRepository<T> repo;

    Person(IRepository<T> repo)
    {
        this.repo = repo;
    }

    public void Save()
    {
        repo.Save<T>();
    }
}

So when you derive Teacher and Student from Person<T> you pass correspondent T, like

class Student : Person<Student>
{
    private IRepository<Student> repo;

    Person(IRepository<Student> repo):base(repo)
    {
       ...
    }    
}

This shall give you the ability to work with List without Reflection or switch kung fu.