Procedure 1.1. Customizing the schema

1. Set the length, precision, and scale of mapping elements.

   Many Hibernate mapping elements define optional attributes named length, precision, and scale.

   
   <property name="zip" length="5"/>
   
   <property name="balance" precision="12" scale="2"/>
   
   

2. Set the not-null, UNIQUE, unique-key attributes.

   The not-null and UNIQUE attributes generate constraints on table columns.

   The unique-key attribute groups columns in a single, unique key constraint. The attribute overrides the name of any generated unique key constraint.

   
   <many-to-one name="bar" column="barId" not-null="true"/>
   
   <element column="serialNumber" type="long" not-null="true" unique="true"/>
   
   
   
   <many-to-one name="org" column="orgId" unique-key="OrgEmployeeId"/>
   
   <property name="employeeId" unique-key="OrgEmployee"/>
   
   

3. Set the index and foreign-key attributes.

   The index attribute specifies the name of an index for Hibernate to create using the mapped column or columns. You can group multiple columns into the same index by assigning them the same index name.

   A foreign-key attribute overrides the name of any generated foreign key constraint.

   
   <many-to-one name="bar" column="barId" foreign-key="FKFooBar"/>
   
   

4. Set child <column> elements.

   Many mapping elements accept one or more child <column> elements. This is particularly useful for mapping types involving multiple columns.

   
   <property name="name" type="my.customtypes.Name"/>
   
       <column name="last" not-null="true" index="bar_idx" length="30"/>
   
       <column name="first" not-null="true" index="bar_idx" length="20"/>
   
       <column name="initial"/>
   
   </property>
   
   

5. Set the default attribute.

   The default attribute represents a default value for a column. Assign the same value to the mapped property before saving a new instance of the mapped class.

   
   <property name="credits" type="integer" insert="false">
   
       <column name="credits" default="10"/>
   
   </property>
   
   <version name="version" type="integer" insert="false">
   
       <column name="version" default="0"/>
   
   </version>
   
   

6. Set the sql-type attribure.

   Use the sql-type attribute to override the default mapping of a Hibernate type to SQL datatype.

   
   <property name="balance" type="float">
   
       <column name="balance" sql-type="decimal(13,3)"/>
   
   </property>
   
   

7. Set the check attribute.

   use the check attribute to specify a check constraint.

   
   <property name="foo" type="integer">
   
     <column name="foo" check="foo > 10"/>
   
   </property>
   
   <class name="Foo" table="foos" check="bar < 100.0">
   
     ...
   
     <property name="bar" type="float"/>
   
   </class>
   
   

8. Add <comment> elements to your schema.

   Use the <comment> element to specify comments for the generated schema.

   
   <class name="Customer" table="CurCust">
   
     <comment>Current customers only</comment>
   
     ...
   
   </class>