23. Legacy Domain Model

Example 389. Declaring a version property in hbm.xml

<!--
  ~ Hibernate, Relational Persistence for Idiomatic Java
  ~
  ~ License: GNU Lesser General Public License (LGPL), version 2.1 or later.
  ~ See the lgpl.txt file in the root directory or <http://www.gnu.org/licenses/lgpl-2.1.html>.
  -->
<version
    column="version_column"
    name="propertyName"
    type="typename"
    access="field|property|ClassName"
    unsaved-value="null|negative|undefined"
    generated="never|always"
    insert="true|false"
    node="element-name|@attribute-name|element/@attribute|."
/>

column	The name of the column holding the version number. Optional, defaults to the property name.
name	The name of a property of the persistent class.
type	The type of the version number. Optional, defaults to `integer`.
access	Hibernate’s strategy for accessing the property value. Optional, defaults to `property`.
unsaved-value	Indicates that an instance is newly instantiated and thus unsaved. This distinguishes it from detached instances that were saved or loaded in a previous session. The default value, `undefined`, indicates that the identifier property value should be used. Optional.
generated	Indicates that the version property value is generated by the database. Optional, defaults to `never`.
insert	Whether or not to include the `version` column in SQL `insert` statements. Defaults to `true`, but you can set it to `false` if the database column is defined with a default value of `0`.

Example 390. The timestamp element in hbm.xml

<!--
  ~ Hibernate, Relational Persistence for Idiomatic Java
  ~
  ~ License: GNU Lesser General Public License (LGPL), version 2.1 or later.
  ~ See the lgpl.txt file in the root directory or <http://www.gnu.org/licenses/lgpl-2.1.html>.
  -->
<timestamp
    column="timestamp_column"
    name="propertyName"
    access="field|property|ClassName"
    unsaved-value="null|undefined"
    source="vm|db"
    generated="never|always"
    node="element-name|@attribute-name|element/@attribute|."
/>

column	The name of the column which holds the timestamp. Optional, defaults to the property name
name	The name of a JavaBeans style property of Java type `Date` or `Timestamp` of the persistent class.
access	The strategy Hibernate uses to access the property value. Optional, defaults to `property`.
unsaved-value	A version property which indicates than instance is newly instantiated, and unsaved. This distinguishes it from detached instances that were saved or loaded in a previous session. The default value of `undefined` indicates that Hibernate uses the identifier property value.
source	Whether Hibernate retrieves the timestamp from the database or the current JVM. Database-based timestamps incur an overhead because Hibernate needs to query the database each time to determine the incremental next value. However, database-derived timestamps are safer to use in a clustered environment. Not all database dialects are known to support the retrieval of the database’s current timestamp. Others may also be unsafe for locking, because of lack of precision.
generated	Whether the timestamp property value is generated by the database. Optional, defaults to `never`.