Hibernate 3 Formulas

one-to-one

In Hibernate, one-to-one is mainly used for two tables sharing the same primary key. For foreign key association, we normally use many-to-one instead. However, with formula, one-to-one is able to link up tables via a foreign key. The above many-to-one example can be mapped by one-to-one as follows:

<hibernate-mapping>

  <class name="Company" table="Company" >

    <id name="id" />

    <one-to-one name="defaultContactPerson" 

        property-ref="defaultContactPerson" >

    <formula>id</formula>

    <formula>1</formula>

    </many-to-one>

  </class>

  <class name="Person" >

    <id name="id" />

    <properties name="defaultContactPerson">

      <property name="companyID" />

      <property name="defaultFlag" />

    </properties>

   </class>

</hibernate-mapping>

Others: many-to-many

formula can be used with a many-to-many element for a special joining from relationship table to an entity table, although this is not often needed.

Summary

The examples in this article show most of the formula usage scenarios. When a formula evaluation value is needed, the formula expression will appear in the select part of the resulting SQL statement. And when a formula is used for joining, it appears in the where part of the resulting SQL statement. Furthermore, a formula expression can use any dialect of SQL, as long as the target database can support it. As a result, formula helps achieve fine-grained mapping from data model to object model without code.

Resources

• Sample code for this article.
• Hibernate provides most information about Hibernate ORM.
• Filter Article on TheServerSide for external filter introduction.
• Spring is a very friendly framework and provides integration with Hibernate and other data access tools.
• "Dependency Injection:" A definitive introduction of dependency injection.
• Dependency Injection Basics: An easy-to-understand introduction of dependency injection.

Dai Yifan is a technical consultant for a leading banking solution provider

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