JPA多对一映射示例.pdf

JPA 多对⼀映射⽰例 JPA教程 - JPA多对⼀映射⽰例 以下代码显⽰了如何进⾏多对⼀映射。 它创建两个实体，⼈员和部门。⼀个部门可以 很多⼈。 在Person类的部门字段中，它⽤@ManyToOne注释标记部门。 @Entity public class Person { @Id @GeneratedValue(strategy=GenerationType.IDENTITY private long id; private String name; @ManyToOne (cascade=CascadeType.ALL private Department department; 例⼦ 下⾯的代码来⾃Person .j ava 。 package mon; 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 { = 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 { = name; } @Override public String toString( { return Person [id= + id + , name= + name + ]; } } 下⾯的代码来⾃PersonDaoImpl .j ava 。 package mon; 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.persis