context.cs

    public override int SaveChanges()
    {
      try
      {
        return base.SaveChanges();
      }
      catch (DbEntityValidationException ex)
      {
        // Retrieve the error messages as a list of strings.
        var errorMessages = ex.EntityValidationErrors
          .SelectMany(x => x.ValidationErrors)
          .Select(x => x.ErrorMessage);

        // Join the list to a single string.
        var fullErrorMessage = string.Join("; ", errorMessages);

        // Combine the original exception message with the new one.
        var exceptionMessage = string.Concat(ex.Message, " The validation errors are: ", fullErrorMessage);

        // Throw a new DbEntityValidationException with the improved exception message.
        throw new DbEntityValidationException(exceptionMessage, ex.EntityValidationErrors);
      }
    }