Definition:

A map is a simple name-value pair list stored on a first rank collection.

Scenario:

Map Foo.getAges()   //  returns a collection of String name-value pairs

Hibernate Mapping

在hbm.xml中設定如下：

<class name="Foo" table="foo">
    ...
    <map role="ages">
        <key column="id"/>
        <index column="name" type="string"/>
        <element column="age" type="string"/>
    </map>
</class>

Table Schema

A simple extra table, Ages, is used to store the name and age string-value pair. Note that the map needs its own identity column too: id

Bidirectionality:

Bidirectionality has no meaning for a map.