Hibernate follows the some basic element for the mapping. It is possible to map properties of one class to serval tables that have a one to one relationship.It can be done Using the <join> element.
Example:
<join
table="tablename"
schema="owner"
catalog="catalog"
fetch="join|select"
inverse="true|false"
optional="true|false">
<key ... /> <property ... /> ... </join>
To understand the above code we given the description of each part of the example below:
|
Tag |
Description |
|
table |
It sows the name of the table. |
|
schema(optional) |
It overrides the schema name secified by the root <hibernate-mapping> element. |
|
catalog(optional) |
It override the catalog name specified by the root <hibernate-maping> element. |
|
fetch(optional) |
It found defaults join. If set of join, default hibernate will use an inner join to retrieve a <join> defined by a class or its superclasses. It will use an outer join for a <join> defined by a subclass. If set to select then hibernae will use a sequential select for a <join> defined on a subclass. This will be issued only if a row represent an instance of the subclass. Inner joins will still be used to retrieve a <join> defined by the classes and its superclass. |
|
inverse(optional) |
It found defaults to false. If enabled, Hibernate will not insert or update the properties defined by this join. |
|
otional(optional) |
It defaults set to false. If enabled, hibernate will insert a row only if the properties defined by this join are non-null. It will always use an outer join to retrieve the proerties. |
For this to understand we take a example:
Address information for a person can be mapped to a separate table while preserving value type semantics for all properties:
<class name="Person" table="PERSON">
<id name="id" column="PERSON_ID">...</id>
<join table="ADDRESS"> <key column="ADDRESS_ID"/>
<property name="address"/> <property name="zip"/>
<property name="country"/> </join> ...
In this example this feature is often only useful for legacy data models. We recommend fewer tables than classes and a fine-grained domain model. However, it is useful for switching between inheritance mapping strategies in a single hierarchy, as explained later.