Question

I am trying to create a generic class:

public class ClassName<T>
{
    public T AccessEntity(string id)
    {
        return (from e in ServiceContext.CreateQuery<T>(TableName)
                where e.RowKey == id // error here!
                select e).FirstOrDefault();
    }
}

In this code I am getting error that:

T does not contain the definition for RowKey

but the parameters which will replace the T at runtime have the definition of RowKey. Maybe because complier is not getting the definition for RowKey in T at compile time, that`s why I am getting this error. Can anybody tell me how to solve this issue?

Answer 1

To do that you would need an interface constraint:

interface IHazRowKey {
     string RowKey { get; } 
}

And specify this restriction:

public class classname<T> where T : IHazRowKey {...}

And specify : IHazRowKey on each of the implementations:

public class Foo : IHazRowKey {....}

The existing RowKey member should match it (assuming it is a property, not a field), so you shouldn’t need to add any other extra code. If it is actually a field (which it shouldn’t be, IMO) then:

public class Foo : IHazRowKey {
    string HazRowKey.RowKey { get { return this.RowKey; } }
    ...
}