Discuss adding server side validation to value type model properties by default.

[NTaylorMullen]

Today in MVC6 having the following model:

public class Person
{
    public int Id { get; set; }
}

Will result in client side validation with 0 server side validation (unless specifying BindingBehaviorAttribute with BindingBehavior.Required).

This differs from what happened in MVC5; model state would be invalid due to server side validation opting in ValueType properties. However, in WebAPI not providing a value for a ValueType property when model binding was 100% ok and did not result in any ModelState errors.

Given the different behavior in the old MVC/WebAPI systems we should discuss the right approach for this in MVC6.

Related conversation that spurred this: #2720 (comment)

/cc @rynowak @Eilon @dougbu

[rynowak]

Decision here is to bring back the implicit [BindRequired] for value-types. If you need to make something optional, it can be customized:

• using [BindingBehavior(BindingBehavior.Optional)]
• a custom MMP
• using a nullable type (int?)