@Entity
@Table(name = "EMP", schema = "SCOTT")
public class Emp implements java.io.Serializable {
// Fields
private Short empno;
private Dept dept;
private String ename;
private String job;
private Short mgr;
private Date hiredate;
private Double sal;
private Double comm;
// Constructors
/** default constructor */
public Emp() {
}
/** full constructor */
public Emp(Dept dept, String ename, String job, Short mgr, Date hiredate,
Double sal, Double comm) {
this.dept = dept;
this.ename = ename;
this.job = job;
this.mgr = mgr;
this.hiredate = hiredate;
this.sal = sal;
this.comm = comm;
}
// Property accessors
@Id
@GeneratedValue
@Column(name = "EMPNO", unique = true, nullable = false, precision = 4, scale = 0)
public Short getEmpno() {
return this.empno;
}
public void setEmpno(Short empno) {
this.empno = empno;
}
@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "DEPTNO")
public Dept getDept() {
return this.dept;
}
public void setDept(Dept dept) {
this.dept = dept;
}
@Column(name = "ENAME", length = 10)
public String getEname() {
return this.ename;
}
public void setEname(String ename) {
this.ename = ename;
}
@Column(name = "JOB", length = 9)
public String getJob() {
return this.job;
}
public void setJob(String job) {
this.job = job;
}
@Column(name = "MGR", precision = 4, scale = 0)
public Short getMgr() {
return this.mgr;
}
public void setMgr(Short mgr) {
this.mgr = mgr;
}
@Temporal(TemporalType.DATE)
@Column(name = "HIREDATE", length = 7)
public Date getHiredate() {
return this.hiredate;
}
public void setHiredate(Date hiredate) {
this.hiredate = hiredate;
}
@Column(name = "SAL", precision = 7)
public Double getSal() {
return this.sal;
}
public void setSal(Double sal) {
this.sal = sal;
}
@Column(name = "COMM", precision = 7)
public Double getComm() {
return this.comm;
}
public void setComm(Double comm) {
this.comm = comm;
}
}
类上方的2个注解
@Entity标志这个类是实体
@Table中name属性值为数据库表名, schema属性值就是数据库用户名,默认为"",可以不写,一般来说,写这2个属性就够了.其他不介绍.
属性注解最好写在get方法上方:
1.@id表示这个是OID属性,对应着数据库的主键,注意OID必须为long,int或者short.
2.@GenerateValue 中有2个属性,strategy表示主键生成策略,默认值为StrategyType.AUTO(另外3个值为:IDENTITY,SEQUENCE,TABLE)
其中AUTO表示hibernate自动选择
IDENTITY表示根据底层数据库生成,支持mysql,db2,sqlserver,sybase等数据库
SEQUENCE也由底层数据库生成,支持oracle,db2,postgresql
TABLE表示根据另外的表生成
3.@Column可以配置实体属性与数据库表字段的对应关系
name属性值为表字段名
unique 是否唯一
nullable 是否可以为null
precision 有效位数
scale 小数位数
length 数据长度
insertable 该字段是否可以插入到数据库表中
updateable 该字段是否可以更新
columnDefinition 设置对应的表字段的数据类型,不常用
4.@Temporal它只有一个value属性,所以这个value可以省略,它的值时枚举值TemporalType
TemporalType.DATE 日期 精确到年月日,例如"2015-11-04"
TemporalType.TIME 时间 精确到时分秒,例如"20:00:00"
TemporalType.TIMESTAMP 日期时间 精确到年月日时分秒,例如"2015-11-04 20:00:00"
@BLob
@Clob
5.@Version 版本标志
6.@Transient 表示这个属性时游离的,不会持久化到数据库中
6.@ManyToOne 先占好坑,下次再详细写
7.@JoinColumn
8.@OneToMany
9.@ManyToMany
10.@OneToOne
单独写出来:
联合主键配置,这里随便选了一种实现方法,说实话hibernate的联合主键配置确实麻烦,还不如mybatis.
这种是myeclipse自动生成的
第一个类
@Embeddable
public class BonusId implements java.io.Serializable {
private String ename;
private String job;
private BigDecimal sal;
private BigDecimal comm;
...
}
第二个类
@Entity
@Table(name = "BONUS", schema = "SCOTT")
public class Bonus implements java.io.Serializable {
private BonusId id;
@EmbeddedId
@AttributeOverrides({
@AttributeOverride(name = "ename", column = @Column(name = "ENAME", length = 10)),
@AttributeOverride(name = "job", column = @Column(name = "JOB", length = 9)),
@AttributeOverride(name = "sal", column = @Column(name = "SAL", precision = 22, scale = 0)),
@AttributeOverride(name = "comm", column = @Column(name = "COMM", precision = 22, scale = 0)) })
public BonusId getId() {
return this.id;
}
public void setId(BonusId id) {
this.id = id;
}
}
Sequence主键生成策略,这个有点复杂
首先先建好序列seq_student
class类为
@Entity
@SequenceGenerator(name="seq_t_student" sequenceName='seq_student')
@Table(name="student" schma=""
public class Student{
private long id;
private void setId(long id){
this.id=id;
}
@Id
@GeneratedValue(strategy=Generation.SEQUENCE,generator="seq_t_student")
@Column(name="ID",length=40,nullable=false,unique=true)
public long getId(){
return this.id
}
}
