Required number parameter defaulting to 0 when not included in JSON

Question

I have a model where I am using DataAnnotations to perform validation, such as

public class OrderDTO
{
    [Required]
    public int Id { get; set; }

    [Required]
    public Decimal Amount { get; set; }
}

Then I am checking the ModelState in each request to make sure that the JSON is valid.

However, I am having trouble for number properties such as Amount above. Even though it is set as [Required], if it's not included in the JSON it will skip the ModelState validation because it is automatically defaulted to 0 instead of null, so the model will seem valid even though it isn't.

An easy way to 'fix' this is to set all the number properties as nullable (int?, Decimal?). If I do this, the defaulting to 0 doesn't happen, but I don't like this as a definitive solution as I need to change my model.

Is there a way to set the properties to null if they are not part of the JSON?

Answer 1

Because Decimal is a non-nullable type so you cannot do that. You need Decimal? to bind null value.