Lords & Ladies, this hack is for Hibernate 3.3.1-GA, and solves an error like this: org.hibernate.MappingException: Repeated column in mapping for entity: org.intresting.MyClass column: HACKME_COLUMN (should be mapped with insert="false" update="false") When you use a discriminator column - with SingleTable inheritance -, like this: <class name="MyClass"  .... >    <composite-id name="id" class="MyClassId">      . . .     <key-property name="hackmecolumn"  type="short">                <column name="HACKME_COLUMN"/>             </key-property>      ... </composite-id>  <discriminator column="HACKME_COLUMN" /> ... <subclass name="VeryIntrestingClass"             discriminator-value="21" /> </class> The hack is: change the case of <discriminator column> to lowercase.  <discriminator column="hackme_column" /> - y santo remedio -