"C# - 我可以从具有通用基类型的类派生吗？"

Question

Intro

I am creating an ASP.NET Web API application with Entity Framework. What I need to do is return different representations of the same resource for one URI, depending on user role. For example, api/employees/1 will return two different objects for admin and standard user:

Standard user

public class EmployeeBasic 
{
    public string FirstName { get; set; }
    public string LastName { get; set; }
}

Admin

public class EmployeeExtended : EmployeeBasic 
{
    public decimal Salary { get; set; }
}

The idea and the attempts

For each resource representation, I will need to provide some related classes, let's say Sort Models for example. I was wondering if it is possible to use generic types and inheritance to create a generic repository methods for related representations. I thought of the following way of doing this:

1. Create some base interface for Sort Models:

    public interface ISortModel<out TBusinessEntity> { // }

2. Create generic SortModel as a base type for all sort models

    public abstract class SortModel<TDBEntity, TBusinessEntity> : ISortModel<TBusinessEntity> { // Database sorting public abstract IQueryable<TDBEntity> ApplyToQuery(IQueryable<TDBEntity> query); // Local sorting public abstract IEnumerable<TBusinessEntity> ApplyToLocal(IEnumerable<TBusinessEntity> localList); // ... // Some private logic (expression mappers, etc.) }

3. Create sort model for basic resource

    public class EmployeeBasicSortModel : SortModel<DBModel.Employee, EmployeeBasic> { public int FullName { get; set; } public override IQueryable<DBModel.Employee> ApplyToQuery(IQueryable<DBModel.Employee> query) { // implementation } public override IEnumerable<EmployeeBasic> ApplyToLocal(IEnumerable<EmployeeBasic> localList) { // implementation } }

4. Extend the basic sort model and add sorting for the extended resource properties

    public class EmployeeExtendedSortModel : EmployeeBasicSortModel //, ... Is it possible to somehow do that? { public override IEnumerable<EmployeeExtended> ApplyToLocal(IEnumerable<EmployeeExtended> localList) { var partiallyOrderedList = base.ApplyToLocal(localList); // Add extended sorting } // ... ? }

5. Use the above classes to create generic service:

    class EmployeesService() { public IList<TEmployee> GetAll<TEmployee>(ISortModel<TEmployee> sortModel) where TEmployee : BasicEmployee { // implementation } }

The problem

When I thought about it for the first time, it seemed pretty simple. But when I started implementing this, I couldn't figure out the way to implement Step 4. Either I am missing something in my C# knowledge (which is quite possible) or this is not possible in the way I am trying to do this.

So the question is: can I create a base class with generic type, derive from it with basic resource as a type and derive one more time with the extended class?

Answer 1

Holy goodness this is a complicated question. The generics are a huge red herring. Ignore the generics; the problem is more fundamental. Let's simplify it greatly.

class Animal {}
class Mammal : Animal {}
class Tiger : Mammal {}

class Shape {}
class Square : Shape {}
class GreenSquare : Square {}

class B
{
  public virtual Mammal Frob(Square s) { ... }
}

class D : B
{
  public override SomeReturnType Frob(SomeArgumentType m) { ... }
}