JPA教程 - JPA 多对多连接表示例
以下代码显示如何为多对多映射设置连接表。
例子
下面的代码来自PersonDaoImpl.java。
package cn.w3cschool.common;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
import org.springframework.transaction.annotation.Transactional;
@Transactional
public class PersonDaoImpl {
public void test(){
Department d1 = new Department();
d1.setName("Design");
Department d2 = new Department();
d2.setName("Testing");
Person p1 = new Person("Tom");
p1.getDepartments().add(d1);
p1.getDepartments().add(d2);
Person p2 = new Person("Jack");
p2.getDepartments().add(d1);
p2.getDepartments().add(d2);
d1.getPersons().add(p1);
d1.getPersons().add(p2);
em.persist(p1);
em.persist(p2);
em.persist(d1);
em.persist(d2);
}
@PersistenceContext
private EntityManager em;
}
下面的代码来自Person.java。
package cn.w3cschool.common;
import java.util.HashSet;
import java.util.Set;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.JoinTable;
import javax.persistence.ManyToMany;
@Entity
public class Person {
@Id
@GeneratedValue(strategy=GenerationType.IDENTITY)
private long id;
private String name;
@ManyToMany
@JoinTable(name="PERSON_DEPT",
joinColumns=@JoinColumn(name="PERSON_ID"),
inverseJoinColumns=@JoinColumn(name="DEPT_ID"))
private Set<Department> departments = new HashSet<Department>();
public Person() {}
public Person(String name) {
this.name = name;
}
public Set<Department> getDepartments() {
return departments;
}
public void setDepartments(Set<Department> departments) {
this.departments = departments;
}
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Override
public String toString() {
return "Person [id=" + id + ", name=" + name + ", departments="
+ departments + "]";
}
}
下面的代码来自Department.java。
package cn.w3cschool.common;
import java.util.HashSet;
import java.util.Set;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.ManyToMany;
@Entity
public class Department implements java.io.Serializable{
@Id
@GeneratedValue(strategy=GenerationType.IDENTITY)
private long id;
private String name;
@ManyToMany
private Set<Person> persons = new HashSet<Person>();
public Set<Person> getPersons() {
return persons;
}
public void setPersons(Set<Person> persons) {
this.persons = persons;
}
public long getId() {
return id;
}
public void setId(long id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Override
public String toString() {
return "Department [id=" + id + ", name=" + name + ", persons=" + persons
+ "]";
}
}
以下是数据库转储。
Table Name: DEPARTMENT
Row:
Column Name: ID,
Column Type: BIGINT:
Column Value: 1
Column Name: NAME,
Column Type: VARCHAR:
Column Value: Design
Row:
Column Name: ID,
Column Type: BIGINT:
Column Value: 2
Column Name: NAME,
Column Type: VARCHAR:
Column Value: Testing
Table Name: DEPARTMENT_PERSON
Row:
Column Name: DEPARTMENT_ID,
Column Type: BIGINT:
Column Value: 1
Column Name: PERSONS_ID,
Column Type: BIGINT:
Column Value: 1
Row:
Column Name: DEPARTMENT_ID,
Column Type: BIGINT:
Column Value: 1
Column Name: PERSONS_ID,
Column Type: BIGINT:
Column Value: 2
Table Name: PERSON
Row:
Column Name: ID,
Column Type: BIGINT:
Column Value: 1
Column Name: NAME,
Column Type: VARCHAR:
Column Value: Tom
Row:
Column Name: ID,
Column Type: BIGINT:
Column Value: 2
Column Name: NAME,
Column Type: VARCHAR:
Column Value: Jack
Table Name: PERSON_DEPT
Row:
Column Name: PERSON_ID,
Column Type: BIGINT:
Column Value: 1
Column Name: DEPT_ID,
Column Type: BIGINT:
Column Value: 1
Row:
Column Name: PERSON_ID,
Column Type: BIGINT:
Column Value: 1
Column Name: DEPT_ID,
Column Type: BIGINT:
Column Value: 2
Row:
Column Name: PERSON_ID,
Column Type: BIGINT:
Column Value: 2
Column Name: DEPT_ID,
Column Type: BIGINT:
Column Value: 1
Row:
Column Name: PERSON_ID,
Column Type: BIGINT:
Column Value: 2
Column Name: DEPT_ID,
Column Type: BIGINT:
Column Value: 2