Hibernate Annotation 学习-白红宇

Hibernate Annotation 学习

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发布时间：2019-06-22

本文共 4230 字，大约阅读时间需要 14 分钟。

1、一对多关联，级联操作

@OneToMany(mappedBy = "paymentad", cascade = CascadeType.ALL, fetch = FetchType.LAZY, targetEntity = PaymentAdHistory.class)

public List<PaymentAdHistory> getPaymentHis() {

return paymentHis;

}

PaymentAdHistory类中

@ManyToOne(cascade = { CascadeType.MERGE })

@JoinColumn(name = "PAYMENTAD")

@NotFound(action = NotFoundAction.IGNORE)

public PaymentAd getPaymentad() {

return paymentad;

}

2、刷新

Adagent aa =adagentDao.get(id);

adagentDao.getSession().refresh(aa);

3、Hibernate Annotation (Hibernate 注解)

中文说明：

==============================================================================

CascadeType.REFRESH：级联刷新，当多个用户同时作操作一个实体，为了用户取到的数据是实时的，在用实体中的数据之前就可以调用一下refresh()方法！

CascadeType.REMOVE：级联删除，当调用remove()方法删除Order实体时会先级联删除OrderItem的相关数据！

CascadeType.MERGE：级联更新，当调用了Merge()方法，如果Order中的数据改变了会相应的更新OrderItem中的数据，

CascadeType.ALL：包含以上所有级联属性。

（注：以上几种级联操作，只能实在满足数据库的约束时才能生效，比如上边的Order和OrderItem存在主外键关联所以执行REMOVE()方法时是不能实现级联删除的）

CascadeType.PERSIST：级联保存，当调用了Persist() 方法，会级联保存相应的数据

2、级联删除

摘自：

school和userMember是一对多关系：
SchoolInfo.java

1import javax.persistence.CascadeType;

import javax.persistence.Column;

import javax.persistence.Entity;

import javax.persistence.FetchType;

import javax.persistence.GeneratedValue;

import javax.persistence.Id;

import javax.persistence.OneToMany;

import javax.persistence.Table;

import javax.persistence.Temporal;

import javax.persistence.TemporalType;

import org.hibernate.annotations.Formula;

import org.hibernate.annotations.GenericGenerator;

@Entity

@Table(name = "school_info")

public class SchoolInfo implements java.io.Serializable {

@Id

@GeneratedValue(generator = "system-uuid")

@GenericGenerator(name = "system-uuid", strategy = "uuid")

private String id;//hibernate的uuid机制,生成32为字符串

@Column(name = "actcodeId", updatable = false, nullable = true, length = 36)

private String actcodeId;

@Formula("select COUNT(*) from school_info")

private int count;

@Temporal(TemporalType.TIMESTAMP)//不用set,hibernate会自动把当前时间写入

@Column(updatable = false, length = 20)

private Date createTime;

@Temporal(TemporalType.TIMESTAMP)

private Date updateTime;// 刚开始我默认insertable=false,但会读取出错提示如下:

// Value '0000-00-00' can not be represented as java.sql.Timestamp

// mappedBy="school"就相当于inverse=true,(mappedBy指定的是不需要维护关系的一端)

// 应该注意的是mappedBy值对应@ManyToOne标注的属性,我刚开始写成"schoolId",让我郁闷了好一会

@OneToMany(mappedBy = "school", cascade = CascadeType.ALL, fetch = FetchType.EAGER, targetEntity = UserMember.class)

// 用范性的话,就不用targetEntity了

private List<usermember> users = </usermember>new ArrayList<usermember>(); </usermember>

}

@GeneratedValue(strategy=GenerationType.AUTO)我们常用的自增长机制,我这里采用的是hibernate的uuid生成机制.
需要注意的是import javax.xx.Entity ，而不是org.hibernate.xx.Entity。

郁闷的是我上面用到@Formula,生成的sql竟然是'select COUNT(*) from school_info as formula0_ from school_info schoolinfo0_,当然不能执行了,寻求正解中~!!!!!!!!!
UserMember.java(前面引入的包已经贴过了,下面就不贴了)

1 @Entity

2 @Table(name = "teacher_info")//实体类和数据库表名不一致时,才用这个

3 public class UserMember implements java.io.Serializable {

5 @Id

6 @GeneratedValue(generator = "system-uuid")

7 @GenericGenerator(name = "system-uuid", strategy = "uuid")

8 private String id;

10 @Column(updatable = false, nullable = false, length = 20)

11 private String logonName;

13 @Temporal(TemporalType.TIMESTAMP)

14 @Column(updatable = false, length = 20)

15 private Date createTime;