namespace Test
{
    public enum TestEnum
    {
        x1 = 1,
        x2 = 2,
        x3 = 3
    }

    public class TestClass
    {
        public long id { get; set; }
        public TestEnum field { get; set; }
    }
}

<class name="TestClass" table="test_classes">
    <id name="id" type="long">
      <generator class="identity" />
    </id>
    <property name="field" type="byte" not-null="true" />
</class>