What exactly does MvcOptions.SuppressImplicitRequiredAttributeForNonNullableReferenceTypes change?

Question

As far as I understand it, value types implicitly have the [Required] attribute when MvcOptions.SuppressImplicitRequiredAttributeForNonNullableReferenceTypes is set to false. But I frankly can't see any difference when I switch it between the two.

Furthermore, if i explicitly use the [Required] attribute on a non-nullable type, such as an int, it will require of me to set its value, rather than just hitting the endpoint without the given int parameter, which would be assigned a default value for its type - 0.

So, to summarize:

1. If it implicitly adds the [Required] attribute, why does the explicit variant offer completely different functionality?

2. Is there any functional difference for enabling/disabling MvcOptions.SuppressImplicitRequiredAttributeForNonNullableReferenceTypes? From what I can see, it doesn't change anything.

Answer 1

I actually haven't tried this setting yet, but I think the clue is in the name: SuppressImplicitRequiredAttributeForNonNullableReferenceTypes.

Sounds like it doesn't apply to value types. It applies to non-nullable reference types.

As you said, a property with type int will always have a default value, the model validator doesn't know if the value was missing or if it was set to that.

However, if you enable C# 8 nullable reference types, you could have properties like:

public string A { get; set; }

public string? B { get; set; }

Now with that setting set the A property gets the Required attribute. It is still a reference type and can be null. Thus the check makes sense.