Validation failed for one or more entities.

 验证失败后用DbEntityValidationException 查找出错的字段

           try
            {
                // Your code...
                // Could also be before try if you know the exception occurs in SaveChanges

                int effect = await _unitOfWorkAsync.SaveChangesAsync();
            }
            catch (System.Data.Entity.Validation.DbEntityValidationException e)
            {
                foreach (var eve in e.EntityValidationErrors)
                {
                    Console.WriteLine("Entity of type "{0}" in state "{1}" has the following validation errors:",
                        eve.Entry.Entity.GetType().Name, eve.Entry.State);
                    foreach (var ve in eve.ValidationErrors)
                    {
                        Console.WriteLine("- Property: "{0}", Error: "{1}"",
                            ve.PropertyName, ve.ErrorMessage);
                    }
                }
                throw;
            }