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We also need to create the employee and project tables along with the employee_project join table with employee_id and project_id as foreign keys:
CREATE TABLE `employee` (
`employee_id` int(11) NOT NULL AUTO_INCREMENT,
`first_name` varchar(50) DEFAULT NULL,
`last_name` varchar(50) DEFAULT NULL,
PRIMARY KEY (`employee_id`)
) ENGINE=InnoDB AUTO_INCREMENT=17 DEFAULT CHARSET=utf8;
CREATE TABLE `project` (
`project_id` int(11) NOT NULL AUTO_INCREMENT,
`title` varchar(50) DEFAULT NULL,
PRIMARY KEY (`project_id`)
) ENGINE=InnoDB AUTO_INCREMENT=18 DEFAULT CHARSET=utf8;
CREATE TABLE `employee_project` (
`employee_id` int(11) NOT NULL,
`project_id` int(11) NOT NULL,
PRIMARY KEY (`employee_id`,`project_id`),
KEY `project_id` (`project_id`),
CONSTRAINT `employee_project_ibfk_1`
FOREIGN KEY (`employee_id`) REFERENCES `employee` (`employee_id`),
CONSTRAINT `employee_project_ibfk_2`
FOREIGN KEY (`project_id`) REFERENCES `project` (`project_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
@Entity
@Table(name = "Employee")
public class Employee {
// ...
@ManyToMany(cascade = { CascadeType.ALL })
@JoinTable(
name = "Employee_Project",
joinColumns = { @JoinColumn(name = "employee_id") },
inverseJoinColumns = { @JoinColumn(name = "project_id") }
)
Set<Project> projects = new HashSet<>();
// standard constructor/getters/setters
}
****************************
@Entity
@Table(name = "Project")
public class Project {
// ...
@ManyToMany(mappedBy = "projects")
private Set<Employee> employees = new HashSet<>();
// standard constructors/getters/setters
}
In order to see the many-to-many annotation in action, we can write the following JUnit test:
public class HibernateManyToManyAnnotationMainIntegrationTest {
private static SessionFactory sessionFactory;
private Session session;
// ...
@Test
public void givenData_whenInsert_thenCreatesMtoMrelationship() {
String[] employeeData = { "Peter Oven", "Allan Norman" };
String[] projectData = { "IT Project", "Networking Project" };
Set<Project> projects = new HashSet<>();
for (String proj : projectData) {
projects.add(new Project(proj));
}
for (String emp : employeeData) {
Employee employee = new Employee(emp.split(" ")[0],
emp.split(" ")[1]);
assertEquals(0, employee.getProjects().size());
employee.setProjects(projects);
session.persist(employee);
assertNotNull(employee);
}
}
@Test
public void givenSession_whenRead_thenReturnsMtoMdata() {
@SuppressWarnings("unchecked")
List<Employee> employeeList = session.createQuery("FROM Employee")
.list();
assertNotNull(employeeList);
for(Employee employee : employeeList) {
assertNotNull(employee.getProjects());
}
}
// ... } ## Security: a humorous overview
