1. Simple Association (one-to-one)
Definition: Our first relationship
is a simple association. In this relationship, one first-rank class holds a
reference to a single instance of another first-rank class and they are
related by a common PK.
Scenario: We have two first-rank classes, Foo and Bar which are related to
each other as follows:
|
Bar Foo.getBar() // returns corresponding Bar instance |
Hibernate Mapping:
In Hibernate, this could be mapped as follows:
|
<class name="Foo" table="foo" ... <one-to-one name="bar" class="Bar"/> </class> |
Table Schema:
|
Foo |
|
id |
|
Bar |
|
id |
No extra columns are needed to support this relationship. Instead both Foo and Bar must share the same PK values to be part of a one-to-one assocation.
If you create suitable instances of Foo and Bar with a shared PK, then retrieving a Foo will automatically retrieve the corresponding Bar.
Bidirectionality:
This relationship can be bidrectional, with Bar having getFoo(), by simply adding a similar mapping and Foo property to Bar.