Hibernate常用的注解

喜欢使用注解的方式，感觉没有xml那么繁琐，下面是转来的一些常用注解

文章转自：

http://bask.iteye.com/blog/212632

@Entity							--声明为一个实体bean
@Table(name="promotion_info")	--为实体bean映射指定表(表名="promotion_info)
@Id								--声明了该实体bean的标识属性
@GeneratedValue					--可以定义标识字段的生成策略.
@Transient						--将忽略这些字段和属性,不用持久化到数据库
@Column(name="promotion_remark")--声明列(字段名="promotion_total") 属性还包括(length=200等)
@Temporal(TemporalType.TIMESTAMP)--声明时间格式
@Enumerated						--声明枚举
@Version						--声明添加对乐观锁定的支持
@OneToOne						--可以建立实体bean之间的一对一的关联
@OneToMany						--可以建立实体bean之间的一对多的关联
@ManyToOne						--可以建立实体bean之间的多对一的关联
@ManyToMany						--可以建立实体bean之间的多对多的关联
@Formula						--一个SQL表达式，这种属性是只读的,不在数据库生成属性(可以使用sum、average、max等)
@OrderBy                        --Many端某个字段排序(List)

时间的处理

Import java.util.Date;
.......
private Date uploadtime;
//设置时间格式
@Temporal(TemporalType.TIMESTAMP)
public Date getUploadtime() {
	return uploadtime;
}
public void setUploadtime(Date uploadtime) {
	this.uploadtime = uploadtime;
}

 以上是基本常用注解，下面是例子说明 

@Entity
@Table(name="promotion_info")
public class Promotion implements Serializable {

	//AUTO--可以是identity类型的字段,或者sequence类型或者table类型,取决于不同的底层数据库
	@Id 
	@GeneratedValue(strategy = GenerationType.AUTO)
	//对于oracle想使用各自的Sequence:
	//@GeneratedValue(strategy = GenerationType.AUTO,generator="PROMOTION_SEQ")
	//@SequenceGenerator(name="PROMOTION_SEQ",sequenceName="PROMOTION_SEQ")
	private Long id;

	@Column(name="group_start_amount")
	private Integer groupStartAmount=0;
	
	@Column(name="promotion_remark",length=200)
	//@Lob 如果是文章内容可以使用 只需要把length=200去掉就可以了
	private String remark;
	//DATE		- java.sql.Date
    //TIME		- java.sql.Time
    //TIMESTAMP - java.sql.Timestamp
	@Temporal(TemporalType.TIMESTAMP)
	@Column(name="start_time")
	private Date startTime;

	//显示0 隐藏1
	public static enum DisplayType {
		显示,隐藏
	}
	@Enumerated(value = EnumType.ORDINAL)//ORDINAL序数
	private DisplayType displayType = DisplayType.显示;

	@Version
	private Integer version;

	//CascadeType.PERSIST	-- 触发级联创建(create)
	//CascadeType.MERGE		-- 触发级联合并(update)
	//FetchType.LAZY		-- 延迟加载
	@ManyToOne(cascade = {CascadeType.PERSIST,CascadeType.MERGE},fetch = FetchType.LAZY)
	private PromotionGroup promotionGroup;

	//单向ManyToMany
	//@JoinTable(关联的表名)
	//joinColumns -- promotion关联的列的外键
	//inverseJoinColumns -- largess 关联列的外键
	@ManyToMany(cascade = {CascadeType.PERSIST,CascadeType.MERGE})
	@JoinTable(name="promotion_largess",joinColumns={@JoinColumn(name="promotion_id")},inverseJoinColumns={@JoinColumn(name="largess_id")})
	private Set<Largess> largess; 
	
	@OneToMany(mappedBy="promotion",cascade = CascadeType.ALL)
	@OrderBy("quantity asc")//item中的列表会根据quantity排序
	private List<PromotionItem> promotionItem;

	//get set 省略....
	@Transient
	private Long hashcodeValue = null;
	public synchronized int hashCode() {
		if(hashcodeValue = null) {
			if(id == null)
				hashcodeValue = new Long(super.hashCode());
			else
				hashcodeValue = id;
		}
		return hashcodeValue.intValue();
	}

	public boolean equals(Object obj) {
		Promotion other = (Promotion) obj;
		if(this == other)
			return true;
		if(this.id == null || other.id == null)
			return false;
		return this.id.equals(other.id);
	}

}
@Entity
@Table(name="promotion_group")
public class PromotionGroup implements Serializable {
	@Id 
	@GeneratedValue(strategy = GenerationType.AUTO)
	private Long id;
	
	//mappedBy的值"promotionGroup"指向owner(Promotion)端的关联属性,并且是双向关系
	@OneToMany(mappedBy="promotionGroup",cascade=CascadeType.ALL)
	private List<Promotion> promotion;

	//get set 省略....
}
@Entity
@Table(name="largess")
public class Largess implements Serializable {
	@Id 
	@GeneratedValue(strategy = GenerationType.AUTO)
	private Long id;

	//1.sql语句中的字段和表名都应该和数据库相应,而不是类中的字段,
	//若带有参数如la.id= id,这个=id才是类中属性
	//2.操作字段一定要用别名
	@Formula(select max(la.id) from largess as la)
	private int maxId;

	@Formula(select COUNT(la.id) from largess la)
	private int count;

	@Transient
	private String img

	//get set 省略....
}

 双向的manytomany

@ManyToMany(mappedBy="largess" cascade = {CascadeType.PERSIST,CascadeType.MERGE})  
//@ManyToMany(mappedBy="largess" cascade=CascadeType.ALL)//如果全包就用ALL
@JoinTable(name="promotion_largess",joinColumns={@JoinColumn(name="largess_id")},inverseJoinColumns={@JoinColumn(name="promotion_id")}) 
private Set<Promotion> promotion;