hibernate annotation笔记

school和userMember是一对多关系,一些基本配置就不写了:

SchoolInfo.java

import 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 users = new ArrayList();   

}

@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)

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

public class UserMember implements java.io.Serializable {   

    @Id   
    @GeneratedValue(generator = "system-uuid")   
    @GenericGenerator(name = "system-uuid", strategy = "uuid")   
    private String id;   

    @Column(updatable = false, nullable = false, length = 20)   
    private String logonName;   

    @Temporal(TemporalType.TIMESTAMP)   
    @Column(updatable = false, length = 20)   
    private Date createTime;   

    @Temporal(TemporalType.TIMESTAMP)   
    private Date updateTime;   

    @ManyToOne(cascade = { CascadeType.MERGE })   
    @JoinColumn(name = "schoolId")   
    private SchoolInfo school;   
    //注意该类就不用声明schoolId属性了,如果不用@JoinColumn指明关联的字段,hibernate默认会是school_id.
}