JPA学习记录三（使用jpa映射关联和继承）

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这次进行学习：使用jpa映射关联和继承

还是在上次的代码上进行编写:

首先添加Employee.java

package cn.zl.jpa.domain;import javax.persistence.DiscriminatorColumn;import javax.persistence.DiscriminatorValue;import javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.Id;import javax.persistence.Inheritance;import javax.persistence.InheritanceType;import javax.persistence.JoinColumn;import javax.persistence.ManyToOne;@Entity//选择继承策略//strategy=TABLE_PER_CLASS :设置为该选项表示每个类使用一个表;//strategy=SINGLE_TABLE :设置为该选项表示所有类及其子类共用一个表;//strategy =JOINED : 设置为该选项表示每个类使用子表保存子类比父类多出的属性@Inheritance(strategy=InheritanceType.SINGLE_TABLE)@DiscriminatorColumn(name="type")//鉴别器@DiscriminatorValue("0")public class Employee {@Id@GeneratedValueprivate int id;private String name;@ManyToOne()@JoinColumn(name="depart_id")//可以不用定义，直接默认departprivate Department depart;public int getId() {return id;}public void setId(int id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public Department getDepart() {return depart;}public void setDepart(Department depart) {this.depart = depart;}public String toString(){return "id="+this.id+"name="+this.name;}}

添加Sales.java.继承 Employee

package cn.zl.jpa.domain;import javax.persistence.DiscriminatorValue;import javax.persistence.Entity;@Entity@DiscriminatorValue("3")public class Sales extends Employee {private int sell;public int getSell() {return sell;}public void setSell(int sell) {this.sell = sell;}}

编写Department.java

package cn.zl.jpa.domain;import java.util.Set;import javax.persistence.CascadeType;import javax.persistence.Entity;import javax.persistence.FetchType;import javax.persistence.GeneratedValue;import javax.persistence.Id;import javax.persistence.OneToMany;@Entitypublic class Department {@Id@GeneratedValueprivate int id;private String name;//不是范型，需要加上目标实体//级联设置：级联类型的方法(执行MERGE和PERSIST方法时，会进行级联)，抓取方式，通过mappedBy映射来找到对应的@OneToMany(targetEntity=Employee.class,cascade={CascadeType.MERGE,CascadeType.PERSIST},fetch=FetchType.LAZY,mappedBy="depart")private Set<Employee> emps;public int getId() {return id;}public void setId(int id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public Set<Employee> getEmps() {return emps;}public void setEmps(Set<Employee> emps) {this.emps = emps;}}

测试：

static void addDepart(){EntityManager em=null;try {em = JpaUtil.getEntityManager();EntityTransaction tx = em.getTransaction();tx.begin();Department depart=new Department();depart.setName("depart name");Employee emp1=new Employee();emp1.setDepart(depart);emp1.setName("emp name1");Sales emp3=new Sales();emp3.setDepart(depart);emp3.setName("emp name3");emp3.setSell(100);Set<Employee> emps = new HashSet<Employee>();emps.add(emp1);emps.add(emp3);depart.setEmps(emps);em.persist(depart);tx.commit();} finally {if(em!=null) em.close();}}

截图：

代码下载： http://download.csdn.net/detail/u013030488/9835319

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