The following code shows how to use a join table to link an one-to-many mapping.
It uses @JoinTable
annotation to set up the join table.
@OneToMany @JoinTable(name = "PERSON_DEPT", joinColumns = @JoinColumn(name = "EMP_ID"), inverseJoinColumns = @JoinColumn(name = "PHONE_ID")) private Set<Person> persons = new HashSet<Person>();
The following code is from Department.java.
package com.java2s.common; import java.util.HashSet; import java.util.Set; import javax.persistence.CascadeType; 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.OneToMany; @Entity public class Department { @Id @GeneratedValue(strategy=GenerationType.IDENTITY) private long id; private String name; @OneToMany @JoinTable(name = "PERSON_DEPT", joinColumns = @JoinColumn(name = "EMP_ID"), inverseJoinColumns = @JoinColumn(name = "PHONE_ID")) 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 + "]"; } }
The following code is from Person.java.
package com.java2s.common; import javax.persistence.Entity; import javax.persistence.GeneratedValue; import javax.persistence.GenerationType; import javax.persistence.Id; import javax.persistence.ManyToOne; import javax.persistence.CascadeType; @Entity public class Person { @Id @GeneratedValue(strategy=GenerationType.IDENTITY) private long id; private String name; @ManyToOne (cascade=CascadeType.ALL) private Department department; public Person() {} public Person(String name) { this.name = name; } public Department getDepartment() { return department; } public void setDepartment(Department department) { this.department = department; } 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 + "]"; } }
The following code is from PersonDaoImpl.java.
package com.java2s.common; import java.util.List; import javax.persistence.EntityManager; import javax.persistence.PersistenceContext; import javax.persistence.Query; import org.springframework.transaction.annotation.Transactional; @Transactional public class PersonDaoImpl { public void test(){ Department d = new Department(); d.setName("Design"); Person p1 = new Person("Tom"); p1.setDepartment(d); Person p2 = new Person("Jack"); p2.setDepartment(d); d.getPersons().add(p1); d.getPersons().add(p2); em.persist(p1); em.persist(p2); em.persist(d); } @PersistenceContext private EntityManager em; }
The following is the database dump.
Table Name: DEPARTMENT Row: Column Name: ID, Column Type: BIGINT: Column Value: 1 Column Name: NAME, Column Type: VARCHAR: Column Value: Design Table Name: PERSON Row: Column Name: ID, Column Type: BIGINT: Column Value: 1 Column Name: NAME, Column Type: VARCHAR: Column Value: Tom Column Name: DEPARTMENT_ID, Column Type: BIGINT: Column Value: 1 Row: Column Name: ID, Column Type: BIGINT: Column Value: 2 Column Name: NAME, Column Type: VARCHAR: Column Value: Jack Column Name: DEPARTMENT_ID, Column Type: BIGINT: Column Value: 1 Table Name: PERSON_DEPT Row: Column Name: EMP_ID, Column Type: BIGINT: Column Value: 1 Column Name: PHONE_ID, Column Type: BIGINT: Column Value: 1 Row: Column Name: EMP_ID, Column Type: BIGINT: Column Value: 1 Column Name: PHONE_ID, Column Type: BIGINT: Column Value: 2