Hiberante Collection Mapping Samples

Collection mapping table

HBM Element	Java Interface	Java Implementation
<set>	Set	HashSet
<set> with order	SortedSet	TreeSet
<list>	List	ArrayList
<bag>, <idbag>	Collection	ArrayList
<map>	Map	HashMap
<map> with order	SortedMap	TreeMap
<array>, <primitive-array>	N/A	array

Sample Tables

CREATE TABLE `core_sample_company` (
`companyId` decimal(18,0) NOT NULL,
`companyName` varchar(128) NOT NULL,
`description` varchar(1024) default NULL,
PRIMARY KEY (`companyId`)
);

CREATE TABLE `core_sample_role` (
`roleId` decimal(18,0) NOT NULL,
`roleName` varchar(128) NOT NULL,
`companyId` decimal(18,0) NOT NULL,
`description` varchar(1024) default NULL,
PRIMARY KEY (`roleId`)
);

CREATE TABLE `core_sample_user` (
`userId` decimal(18,0) NOT NULL,
`userName` varchar(128) NOT NULL,
`companyId` decimal(18,0) NOT NULL,
`defaultRoleId` decimal(18,0) default NULL,
`description` varchar(1024) default NULL,
PRIMARY KEY (`userId`)
);

CREATE TABLE `core_sample_user_role` (
`userId` decimal(18,0) NOT NULL,
`roleId` decimal(18,0) NOT NULL,
`pripority` int(11) NOT NULL,
PRIMARY KEY (`userId`,`roleId`)
);

HBM defintion

The definiton of <set>, <bag>, <list> is similar.

Defines a collection whose element type is simple data type.

<class name="SampleCompany" table="core_sample_company">

<bag name="roleNames" table="core_sample_role" lazy="false" >
<key column="companyId"/>
<element column="roleName" type="string"/>
</bag>

</class>

Query HQL: select c.id, c.name, r from SampleCompany c left join c.roleNames r

Defines a collection whose element type is another mapped java class

<class name="SampleCompany" table="core_sample_company">

<bag name="roles" cascade="none">
<key column="companyId"/>
<one-to-many class="SampleRole" not-found="ignore"/>
</bag>

</class>

Query HQL: select c.id, c.name, r.name from SampleCompany c left join c.role r

Pay attention that key column is a foreign column of SampleRole table.

Defines a list with list-index

<list> is not a popular element. It request a index column in table. The index column is the index of java List, it has to be a sequence starts from 0.

<class name="SampleUser" table="core_sample_user">

<list name="roles" table="core_sample_user_role" cascade="all" lazy="false" >
<key><column name="userId" sql-type="integer"/></key>
<index column="priority"></index>
<many-to-many class="SampleRole">
<column name="roleId"></column>
</many-to-many>
</list>

</class>

The benifit of <list> is it alwasy sorts list by index column. However, It is hard to resort the list. I tried remove a role from role list and add it to another poisition. When save the role list, an exception throwed:

java.sql.BatchUpdateException: Duplicate entry 'user001-role003 for key 1

This should be a hibernate bug.

Defines a bag with relationship table

<class name="SampleRole" table="core_sample_role">

<bag name="users" table="core_sample_user_role" cascade="none" lazy="false">
<key><column name="roleId" sql-type="integer"/></key>
<many-to-many class="SampleUser">
<column name="userId"></column>
</many-to-many>
</bag>

</class>

• Key column is foreign column from relationship table to current table(SampleRole>
• many-to-many sub column is foreign column from relationship table to target table (SampleUser)

Technorati : Hibernate, Java