12. Components

A typical component mapping looks as this:

Definition: Components are Java classes that are populated from selected columns of a parent class' table. This allows second-rank classes to exist within a first-rank class whilst still mapping to a single table for efficiency.

Scenario: We have one first-rank class, Foo, and a second-rank class, FooSecond.

FooSecond Foo.getSecond() // returns enclosed second-rank instance

Hibernate Mapping:
In Hibernate, this could be mapped as follows:

<class name="Foo" table="foo">      ...      <component name="second" class="FooSecond">           <property name="firstName"/>           <property name="lastName"/>      </component> </class>

Table Schema:

Foo
id	firstName	lastName

Here, Foo is mapped using id from table Foo. FooSecond is mapped from the same table using firstName and lastName.

Bidirectionality:
There's no bidirectional relationship available here as there is only one first-rank class involved.