Question

I want to create an interface such as…

interface IRepository<params T>
{
    T GetAll();
}

class PersonRepository : IRepository<Employees,Students>
{
    Employees GetAll();
    Students GetAll();
}

So clearly I know that the concrete implementation is impossible but is there any way to take a multi entity repostitory and create some super base interface?

Answer 1

Here’s something possible:

namespace ConsoleApplication12
{
    public class Employee
    {
        public string EmpName { get; set; }

        public override string ToString()
        {
            return this.EmpName;
        }
    }

    public class Student
    {
        public string StudName { get; set; }

        public override string ToString()
        {
            return this.StudName;
        }
    }

    public class Other
    {
        public int TestField { get; set; }

        public override string ToString()
        {
            return this.TestField.ToString();
        }
    }

    public interface IRepository<T>
    {
        List<T> GetAll();
    }

    public class PersonRepository : IRepository<Employee>, IRepository<Student>, IRepository<Other>
    {
        List<Student> IRepository<Student>.GetAll()
        {
            return new List<Student> { new Student { StudName = "test2" } };
        }

        List<Other> IRepository<Other>.GetAll()
        {
            return new List<Other> { new Other { TestField = 42 } };
        }

        List<Employee> IRepository<Employee>.GetAll()
        {
            return new List<Employee> { new Employee { EmpName = "test1" } };
        }
    }

    public class Program
    {
        private static void Main(string[] args)
        {
            PersonRepository d = new PersonRepository();

            // Returns "test1"
            Console.WriteLine(((IRepository<Employee>)d).GetAll()[0]);

            // Returns "test2"
            Console.WriteLine(((IRepository<Student>)d).GetAll()[0]);

            // Returns 42
            Console.WriteLine(((IRepository<Other>)d).GetAll()[0]);

            Console.ReadLine();
        }
    }
}

As you can see, you have to explicitly cast your class so your application can known which GetAll() method to call.