This is how Visual Studio tells you that something went wrong while updating your entity.
Simple solution would be to catch System.Data.Entity.Validation.DbEntityValidationException and iterate through EntityValidationErrors collection.
try { return _context.SaveChanges(); } catch (System.Data.Entity.Validation.DbEntityValidationException dbvEx) { List<string> errors = new List<string>(); foreach (var validationErrors in dbvEx.EntityValidationErrors) { foreach (var validationError in validationErrors.ValidationErrors) { errors.Add(string.Format("Property: {0} Error: {1}", validationError.PropertyName, validationError.ErrorMessage)); } } return 0; }