Programming Tutorials

Identity columns and sequences in Hibernate

By: Dorris  

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For databases that support identity columns (DB2, MySQL, Sybase, MS SQL), you can use identity key generation. For databases that support sequences (DB2, Oracle, PostgreSQL, Interbase, McKoi, SAP DB) you can use sequence style key generation. Both of these strategies require two SQL queries to insert a new object. For example:

<id name="id" type="long" column="person_id">

<generator class="sequence">

<param name="sequence">person_id_sequence</param>

</generator>

</id>

<id name="id" type="long" column="person_id" unsaved-value="0">

<generator class="identity"/>

</id>

For cross-platform development, the native strategy will, depending on the capabilities of the underlying database, choose from the identity, sequence and hilo strategies.