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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!