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5. Collection (raw data)


Definition:
A raw data collection is a collection on a first-rank class that contains second-rank classes. First- rank class A holds a reference to a set of second-rank class B instances. This is not limited to full classes - B could even be of primitive type.

Scenario:
We have one first-rank class, Foo, and a collection of Strings (e.g. people's names)

Set Foo.getPeople() // returns a collection of String instances

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

<class name="Foo" table="foo">
      ...
      <set role="people" table="Person">
            <key column="foo_id"/>
           <element column="name" type="string"/>
      </set>
 </class>

Table Schema:

Foo

id

Person

foo_id

name


Note that Person does not represent a first-rank class. It is simply a collection of second-rank persistent data - in this case String objects.

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

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