土豆的小秘密 2007-06-30
school和userMember是一对多关系,一些基本配置就不写了:
SchoolInfo.javaimport 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importjavax.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'selectCOUNT(*)fromschool_infoasformula0_fromschool_infoschoolinfo0_,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. }