The following code shows how to do many to one mapping.
It creates two entities, Person and Department. One Department can have many persons.
In the department field from Person class it marks the Department with
@ManyToOne
annotation.
@Entity public class Person { @Id @GeneratedValue(strategy=GenerationType.IDENTITY) private long id; private String name; @ManyToOne (cascade=CascadeType.ALL) private Department department;
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 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.OneToMany; @Entity public class Department { @Id @GeneratedValue(strategy=GenerationType.IDENTITY) private long id; private String name; @OneToMany(mappedBy="department",cascade=CascadeType.ALL) 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 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: Jack 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: Tom Column Name: DEPARTMENT_ID, Column Type: BIGINT: Column Value: 1