Generic Constraint for Non Nullable types

Question

I have the following class:

public class KeyDTO<T>
{
     public T Id { get; set; }
}

So far so good, but I want the type parameter T to be a non-nullable type. I've read somewhere that this may be feasible:

public class KeyDTO<T> where T : IComparable, IComparable<T>
{
     public T Id { get; set; }
}

But, If i change public T Id to public T? Id, I get a compilation error telling me that T must be non-nullable.

How can I specify that a generic type parameter must be non-nullable?

Edit

I want to accomplish this because I want to annotate my Id property with the [Required] attribute as follows:

public class KeyDTO<T> {
    [Required]
    public T Id { get; set; }
}

What [Required] does is validate the model so T cannot be null.

However, if I have KeyDTO<int>, Id will be initialized to 0, bypassing my [Required] attribute

nalka nalka · Accepted Answer · 2020-02-10T16:21:16

From C# 8.0 you can now use the where T : notnull generic constraint to specificy T is a non-nullable type.