Should I create an interface for abstract class?

Question

Is there any practial reason to create interface for abstract class? I encountered such thing:

public interface IEntity<T> 
{
    T Id { get; set; }
}

public abstract class BaseEntity { 
}

public abstract class Entity<T> : BaseEntity, IEntity<T> 
{
    public virtual T Id { get; set; }
}

and i really don't understand what is the difference between that and this code, because IEntity is not a thing i whould use more than once:

public abstract class BaseEntity { 
}

public abstract class Entity<T> : BaseEntity
{
    public virtual T Id { get; set; }
}

Thanks!

What are you trying to accomplish? What is your goal, and why have you started to solve your problem by doing this? It's impossible to say what is a good idea and what isn't without knowing what problem you are trying to solve. — sara, Mar 21 '16 at 14:25
http://stackoverflow.com/questions/14091837/c-sharp-abstract-class-implementing-an-interface, http://programmers.stackexchange.com/questions/163641/interfaces-on-an-abstract-class, try searching. — CodeCaster, Mar 21 '16 at 14:26
Some guidance from Microsoft: https://msdn.microsoft.com/en-us/library/scsyfw1d%28v=vs.71%29.aspx — Matthew Watson, Mar 21 '16 at 14:29
kai, i want to desribe structure of database entities. I thought that it would be nice to make BaseEntity class with implementation of general properties and inherit other classes from it. — Alexey Koptyaev, Mar 21 '16 at 14:39
@AlexeyKoptyaev The fact that the suggested base-class would contain general properties or methods, is critical for its reason to exist, and it something you should have mentioned in the question. — Maarten, Mar 21 '16 at 14:42
@CodeCaster Thanks, the first link is exatly what i wanted to know. All searches showed only "difference between abstract class and interface". — Alexey Koptyaev, Mar 22 '16 at 07:43

score 0 · Answer 1 · answered Mar 21 '16 at 14:41

Since the BaseEntity class does actually add any properties of methods, yes, it is completely different from the interface. The interface defines a property Id of type T, and that interface (contract) can be used in other locations in your application.

The base class as it is now, is useless IMHO.

A base class which would implement the interface for you is something that would be usable, like this:

public interface IEntity<T> {
    T Id { get; set; }
}

public abstract class BaseEntity<T>: IEntity<T> { 
    public virtual T Id { get; set; }
}

public abstract class Entity<T> : BaseEntity<T> {
    // No need to implement the Id property, we already have it inherited
}

score 0 · Answer 2 · edited May 23 '17 at 12:25

0

Here is the same thing with correct answer that i wanted to know: c# Abstract Class implementing an Interface

Thanks everyone for help.

edited May 23 '17 at 12:25

Community

1
1

answered Mar 22 '16 at 07:56

Alexey Koptyaev

187
2
16

Should I create an interface for abstract class?

2 Answers2