ConstraintException is thrown when posting empty data for non-nullable properties
I am working with model validation in .NET, Entity Framework 4, DataAnnotations and
partial classes with MetadataType connections and now have a problem where exceptions
are thrown when posting empty data for non-nullable properties.
In my model, I have an Employee entity for which some properties are non-nullable.
I also have a partial class and a metadata class, to be used with model validation,
as described in this blog post.
This approach works great. Employee is validated properly, with minimum effort. My
entities are validated with standard validation attributes as well as a set of custom
ones. Lovely.
However, the application crashes when I post empty text. A ConstraintException is
thrown before any view controller actions are executed, which means that I can’t act
on the exception.
The exception occurs since the empty posted data causes the corresponding properties
on the Employee class to be set to null, which conflicts with the non-null setup
in the entity model. However, since I have custom validation classes that use
Required attributes to make properties mandatory, I don’t need the non-nullable
attributes in my model.
As such, I can set the nullable property to (None) and the exception is now history!