For example we have two table called "Employee" and "Project". Each Employee can work on one to many Projects and one Project can have one to many Employee. Here is the database tables
EMPLOYEE
- EMPLOYEE_ID
- EMPLOYEE_NAME
- EMPLOYEE_TYPE
PROJECT
- PROJECT_ID
- PROJECT_TITLE
- PROJECT_DURATION
EMPLOYEE_PROJECT (Join Table)
- EMPLOYEE_ID
- PROJECT_ID
- DATE-ADDED (Extra field)
Domain Modelling
Project.java
public class Project implements Serializable{
private static final long serialVersionUID = 2703915705484865029L;
private String projectId;
private String projectTitle;
private String projectDuration;
private List<ProjectEmployee> employees;
//getters and setters
public void addEmployee(Employee employee, Date dateAdded) {
ProjectEmployee association = new ProjectEmployee();
association.setEmployee(employee);
association.setProject(this);
association.setEmployeeId(employee.getEmployeeId());
association.setProjectId(this.getProjectId());
association.setDateAdded(dateAdded);
this.employees.add(association);
employee.getProjects().add(association);
}
}
Employee.java
public class Employee implements Serializable{
private static final long serialVersionUID = -8821659676348395539L;
private String employeeId;
private String employeeName;
private String employeeType;
private List<ProjectEmployee> projects;
}
ProjectEmployee.java
public class ProjectEmployee implements Serializable{
private static final long serialVersionUID = -2691690907714316448L;
private String employeeId;
private String projectId;
private Date dateAdded;
private Employee employee;
private Project project;
//getters and setters
}
And ProjectEmployeeId.java
public class ProjectEmployeeId implements Serializable{
private static final long serialVersionUID = 3284051729103828873L;
private String employeeId;
private String projectId;
public String getEmployeeId() {
return employeeId;
}
public void setEmployeeId(String employeeId) {
this.employeeId = employeeId;
}
public String getProjectId() {
return projectId;
}
public void setProjectId(String projectId) {
this.projectId = projectId;
}
public int hashCode() {
return (int) (employeeId.hashCode() + projectId.hashCode());
}
public boolean equals(Object object) {
if (object instanceof ProjectEmployeeId) {
ProjectEmployeeId otherId = (ProjectEmployeeId) object;
return (otherId.getEmployeeId() == this.getEmployeeId())
&& (otherId.getProjectId() == this.getProjectId());
}
return false;
}
}
The persistence-mapping.xml file looks like:
<?xml version="1.0" encoding="UTF-8" ?>
<entity-mappings xmlns="http://java.sun.com/xml/ns/persistence/orm"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/persistence/orm
http://java.sun.com/xml/ns/persistence/orm_2_0.xsd"
version="2.0">
<entity class="Employee"
access="FIELD">
<table name="EMPLOYEE" />
<attributes>
<id name="employeeId">
<column name="EMPLOYEE_ID" />
</id>
<basic name="employeeName">
<column name="EMPLOYEE_NAME" />
</basic>
<basic name="employeeType">
<column name="EMPLOYEE_TYPE" />
</basic>
<one-to-many name="projects" fetch="LAZY" mapped-by="employee">
<cascade>
<cascade-all />
</cascade>
</one-to-many>
</attributes>
</entity>
<entity class="Project"
access="FIELD">
<table name="PROJECT" />
<attributes>
<id name="projectId">
<column name="PROJECT_ID" />
</id>
<basic name="projectTitle">
<column name="PROJECT_TITLE" />
</basic>
<basic name="projectDuration">
<column name="PROJECT_DURATION" />
</basic>
<one-to-many name="employees" fetch="LAZY" mapped-by="project">
<cascade>
<cascade-all />
</cascade>
</one-to-many>
</attributes>
</entity>
<entity class="ProjectEmployee">
<table name="EMPLOYEE_PROJECT" />
<id-class class="ProjectEmployeeId"/>
<attributes>
<id name="employeeId">
<column name="EMPLOYEE_ID"/>
</id>
<id name="projectId">
<column name="PROJECT_ID"/>
</id>
<basic name="dateAdded">
<column name="DATE_ADDED" />
</basic>
<many-to-one name="employee" id="true">
<join-column name="EMPLOYEE_ID" updatable="false" insertable="false"/>
</many-to-one>
<many-to-one name="project" id="true">
<join-column name="PROJECT_ID" updatable="false" insertable="false"/>
</many-to-one>
</attributes>
</entity>
</entity-mappings>
Now Create Persistence.xml file and add these:
<?xml version="1.0" encoding="UTF-8" ?>
<persistence version="2.0"
xmlns="http://java.sun.com/xml/ns/persistence"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/persistence
http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd">
<persistence-unit name="example" transaction-type="RESOURCE_LOCAL">
<mapping-file>META-INF/persistence-mapping.xml</mapping-file>
<mapping-file>META-INF/persistence-query.xml</mapping-file>
<class>Employee</class>
<class>Project</class>
<class>ProjectEmployee</class>
<class>ProjectEmployeeId</class>
<properties>
<property name="cache.provider_class" value="org.hibernate.cache.NoCacheProvider"/>
<property name="hibernate.max_fetch_depth" value="3"/>
<property name="hibernate.query.factory_class" value="org.hibernate.hql.classic.ClassicQueryTranslatorFactory"/>
<property name="hibernate.query.substitutions" value="true 1, false 0"/>
<property name="hibernate.show_sql" value="true"/>
<property name="hibernate.dialect" value="org.hibernate.dialect.Oracle9iDialect"/>
<property name="hibernate.hbm2ddl.auto" value="validate"/>
</properties>
</persistence-unit>
</persistence>
And persistence-query.xml as :
<?xml version="1.0" encoding="UTF-8" ?>
<entity-mappings xmlns="http://java.sun.com/xml/ns/persistence/orm"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/persistence/orm
http://java.sun.com/xml/ns/persistence/orm_2_0.xsd"
version="2.0">
<named-query name="project.findAll">
<query>
from Project p
</query>
</named-query>
<named-query name="employee.findAll">
<query>
from Employee e;
</query>
</named-query>
<named-query name="employee.findByProject">
<query>
select e from Employee e JOIN e.projects p where p.project = ?
</query>
</named-query>
</entity-mappings>
Finally Create Test Case as follow:
@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(locations = { "classpath:applicationContext/applicationContext-*.xml" })
@TransactionConfiguration(transactionManager = "transactionManager", defaultRollback = false)
public class ProjectDaoTest {
@Autowired
private ProjectDao projectDao;
@Autowired
private EmployeeDao employeeDao;
@Before
public void before() {
}
@After
public void after() {
}
@Test
@Transactional
public void testProjectAvailability() throws Exception{
Project p = projectDao.findByUuid("BEE9F3A7979F505EE040007F01001B21");
Employee e = new Employee();
e.setEmployeeId(UUIDGenerator.getUUID());
e.setEmployeeName("Peter");
e.setEmployeeType("Contractor");
employeeDao.persistChanges(e);
Employee e = employeeDao.findByUuid("785B9FDDD8DB56B14F13359027636041");
p.addEmployee(e, new Date());
}
@Test
public void testGetAllEmployeeFromProject() {
Project p = projectDao.findByUuid("BEE9F3A7979F505EE040007F01001B21");
List<Employee> employees = employeeDao.findByNamedQueryAndParams("employee.findByProject", p);
Assert.assertNotNull(employees);
}
}
That's All. Enjoy Programming..................
