hibernate3 annotation 的实例 3 (one to many)

http://bigcat.easymorse.com/?p=249

 

在EJB3.0 规范中 多对一与一对多的双向关系， 多对一（就是@ManyToOne注解的这端，是多端哦 不要搞混了）这端总是双向关联端的主题(owner)端， 而一对多端的关联注解为 @OneToMany（mappedBy=" " ）其值是：多对一端的属性

实例三： （一对多）

  CREATE TABLE "ABC"."CLAZZ"
   ( "ID" NUMBER(*,0) NOT NULL ENABLE,
 "CLASSNAME" VARCHAR2(20 BYTE),

 CONSTRAINT "CLAZZ_PK" PRIMARY KEY ("ID"))

 

 CREATE TABLE "ABC"."STUDENT"
   ( "ID" NUMBER(*,0) NOT NULL ENABLE,
 "NAME" VARCHAR2(20 BYTE),
 "BIRTHDAY" DATE,
 "CLAZZID" NUMBER(*,0),
  CONSTRAINT "PK_STUDENT" PRIMARY KEY ("ID"))

 

alter table STUDENT
add constraint student_clazz_fk foreign key
(clazzid) references CLAZZ (id)

import javax.persistence.CascadeType;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.persistence.Table;
import org.hibernate.annotations.GenericGenerator;
import org.hibernate.annotations.Parameter;

@Entity
@Table(name="clazz")
public class Clazz {
 @Id
 @GeneratedValue(generator="cseq")
 @GenericGenerator(name="cseq",strategy="sequence",parameters={@Parameter(name="sequence",value="clazz_seq")})
 private Integer id;
 private String className;
 @OneToMany(cascade=CascadeType.REFRESH,mappedBy="clazz")//一个班级有很多学生
 private Set<Student> students;
 
 public Integer getId() {
  return id;
 }
 public void setId(Integer id) {
  this.id = id;
 }
 public String getClassName() {
  return className;
 }
 public void setClassName(String className) {
  this.className = className;
 }
 public Set<Student> getStudents() {
  return students;
 }
 public void setStudents(Set<Student> students) {
  this.students = students;
 }
}

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import org.hibernate.annotations.GenericGenerator;
import org.hibernate.annotations.Parameter;

@Entity
public class Student {
 @Id
 @GeneratedValue(generator="sseq")
 @GenericGenerator(name="sseq",strategy="sequence",parameters={@Parameter(name="sequence",value="seq_student")})
 private Integer id;
 private String name;
 private Date birthday;
 @ManyToOne
 @JoinColumn(name="clazzid")
 private Clazz clazz;   //和上面的红色的clazz对应
 
 public Integer getId() {
  return id;
 }
 public void setId(Integer id) {
  this.id = id;
 }
 public String getName() {
  return name;
 }
 public void setName(String name) {
  this.name = name;
 }
 public Date getBirthday() {
  return birthday;
 }
 public void setBirthday(Date birthday) {
  this.birthday = birthday;
 }
 public Clazz getClazz() {
  return clazz;
 }
 public void setClazz(Clazz clazz) {
  this.clazz = clazz;
 }
}

 

在delete Clazz的一个对象的时候，出现异常：

Caused by: java.sql.BatchUpdateException: ORA-02292: 违反完整约束条件 (ABC.UC_CLAZZ_FK) - 已找到子记录

但是在Student表中没有和Clazz表有关联的行时可以删除

 解决方法：@OneToMany(cascade={CascadeType.REFRESH,CascadeType.REMOVE},mappedBy="clazz") //添加删除级联