配置持久化类的常用注解
1. @Entity
将一个类声明为一个实体bean(即一个持久化POJO类)。
2. @Table
声明了该实体bean映射指定的表(table),目录(catalog)和schema名字
3. @Id
声明了该实体bean的标识属性(对应表中的主键)。
4. @Column
声明了属性到列的映射。该注解有如下的属性:
name 可选,列名(默认值是属性名)
unique 可选,是否在该列上设置唯一约束(默认值false)
nullable 可选,是否设置该列的值可以为空(默认值false)
insertable 可选,该列是否作为生成的insert语句中的一个列(默认值true)
updatable 可选,该列是否作为生成的update语句中的一个列(默认值true)
columnDefinition 可选,为这个特定列覆盖sql ddl片段(这可能导致无法在不同数据库间移植)
table 可选,定义对应的表(默认为主表)
length 可选,列长度(默认值255)
precision 可选,列十进制精度(decimal precision)(默认值0)
scale 可选,如果列十进制数值范围(decimal scale)可用,在此设置(默认值0)
5. @GeneratedValue
声明了主键的生成策略。该注解有如下属性:
strategy 指定生成的策略(JPA定义的),这是一个GenerationType。默认是GenerationType. AUTO
GenerationType.AUTO 主键由程序控制
GenerationType.TABLE 使用一个特定的数据库表格来保存主键
GenerationType.IDENTITY 主键由数据库自动生成(主要是自动增长类型)
GenerationType.SEQUENCE 根据底层数据库的序列来生成主键,条件是数据库支持序列。这个值要与generator一起使用,generator 指定生成主键使用的生成器(可能是orcale中的序列)。
6. SequenceGenerator
声明了一个数据库序列。该注解有如下属性:
name 表示该表主键生成策略名称,它被引用在@GeneratedValue中设置的“gernerator”值中
sequenceName 表示生成策略用到的数据库序列名称。
initialValue 表示主键初始值,默认为0。
allocationSize 每次主键值增加的大小,例如设置成1,则表示每次创建新记录后自动加1,默认为50。
7. GenericGenerator
声明了一个hibernate的主键生成策略。支持十三种策略。该注解有如下属性:
name 指定生成器名称。
strategy 指定具体生成器的类名(指定生成策略)。
parameters 得到strategy指定的具体生成器所用到的参数。
其十三种策略(strategy属性的值)如下:
● native
对于orcale采用Sequence方式,对于MySQL和SQL Server采用identity(处境主键生成机制),native就是将主键的生成工作将由数据库完成,hibernate不管(很常用)
例:@GeneratedValue(generator = "paymentableGenerator")
@GenericGenerator(name = "paymentableGenerator", strategy = "native")
● uuid
采用128位的uuid算法生成主键,uuid被编码为一个32位16进制数字的字符串。占用空间大(字符串类型)。
例:@GeneratedValue(generator = "paymentableGenerator")
@GenericGenerator(name = "paymentableGenerator", strategy = "uuid")
● hilo
要在数据库中建立一张额外的表,默认表名为hibernate_unque_key,默认字段为integer类型,名称是next_hi(比较少用)。
例:@GeneratedValue(generator = "paymentableGenerator")
@GenericGenerator(name = "paymentableGenerator", strategy = "hilo")
● assigned
在插入数据的时候主键由程序处理(很常用),这是<generator>元素没有指定时的默认生成策略。等同于JPA中的AUTO。
例:@GeneratedValue(generator = "paymentableGenerator")
@GenericGenerator(name = "paymentableGenerator", strategy = "assigned")
● identity
使用SQL Server和MySQL的自增字段,这个方法不能放到Oracle中,Oracle不支持自增字段,要设定sequence(MySQL和SQL Server中很常用)。等同于JPA中的IDENTITY
例:@GeneratedValue(generator = "paymentableGenerator")
@GenericGenerator(name = "paymentableGenerator", strategy = "identity")
● select
使用触发器生成主键(主要用于早期的数据库主键生成机制,少用)
例:@GeneratedValue(generator = "paymentableGenerator")
@GenericGenerator(name = "paymentableGenerator", strategy = "select")
● sequence
调用谨慎数据库的序列来生成主键,要设定序列名,不然hibernate无法找到。
例:@GeneratedValue(generator = "paymentableGenerator")
@GenericGenerator(name = "paymentableGenerator", strategy = "sequence", parameters = { @Parameter(name = "sequence", value = "seq_payablemoney") })
● seqhilo
通过hilo算法实现,但是主键历史保存在Sequence中,适用于支持Sequence的数据库,如Orcale(比较少用)。
例:@GeneratedValue(generator = "paymentableGenerator")
@GenericGenerator(name = "paymentableGenerator", strategy = "seqhilo", parameters = { @Parameter(name = "max_lo", value = "5") })
● increnment
插入数据的时候hibernate会给主键添加一个自增的主键,但是一个hibernate实例就维护一个计数器,所以在多个实例运行的时候不能使用这个方法。
例:@GeneratedValue(generator = "paymentableGenerator")
@GenericGenerator(name = "paymentableGenerator", strategy = "increnment")
● foreign
使用另一个相关的对象的主键。通常和@OneToOne联合起来使用。
例:@Id
@GeneratedValue(generator = "idGenerator")
@GenericGenerator(name = "idGenerator", strategy = "foreign", parameters = { @Parameter(name = "property", value = "info") })
Integer id;
@OneToOne
EmployeeInfo info;
● guid
采用数据库底层的guid算法机制,对应MySQL的uuid()函数,SQL Server的newid()函数,ORCALE的rawtohex(sys_guid())函数等。
例:@GeneratedValue(generator = "paymentableGenerator")
@GenericGenerator(name = "paymentableGenerator", strategy = "guid")
● uuid.hex
参见uuid,建议用uuid替换。
● sequence-identity
sequence策略的扩展,采用立即检索策略来获取sequence值,需要JDBC3.0和JDK4以上(含1.4)版本。
例:@GeneratedValue(generator = "paymentableGenerator")
@GenericGenerator(name = "paymentableGenerator", strategy = "sequence-identity", parameters = { @Parameter(name = "sequence", value = "seq_payablemoney") })
8. @Transient
声明了非持久化属性,即数据库中没有相应的映射字段,是一个普通属性。
9. @Temporal
声明了日期类型。
TemporalType.DATE 日期,例:2011-04-12
TemporalType.TIME 时间,例:22:50:30
TemporalType.TIMESTAMP 日期和时间,例:2011-04-12 22:51:30
10. @Version
声明了对乐观锁定的支持
例:@Version
@Column(name="OPTLOCK")
public Integer getVersion() { ... }
上面这个例子中,version属性将映射到 OPTLOCK列,entity manager使用该字段来检测更新冲突(防止更新丢失,请参考last-commit-wins策略)。
根据EJB3规范,version列可以是numeric类型(推荐方式)也可以是timestamp类型。Hibernate支持任何自定义类型,只要该类型实现了UserVersionType。
注解配置对象关联关系示例:
大配置关联各个持久化类:
<!--一对一双向--> <mapping class="cn.happy.ontoondouble.Emp"/> <mapping class="cn.happy.ontoondouble.IdCard"/> <!--一对多双向--> <mapping class="cn.happy.onetomanydouble.Dept"/> <mapping class="cn.happy.onetomanydouble.Emp"/> <!--多对多双向--> <mapping class="cn.happy.manytomanydouble.Game"/> <mapping class="cn.happy.manytomanydouble.PlayerHome"/>
1.一对一双向
Emp(员工类):
package cn.happy.ontoondouble; import javax.persistence.*; /** * Created by CKW on 2017/2/4. */ @Entity @Table(name="EMP1") public class Emp{ private Integer empno; @Column private String empname; private IdCard idCard; @OneToOne @JoinColumn(name = "iid") public IdCard getIdCard() { return idCard; } public void setIdCard(IdCard idCard) { this.idCard = idCard; } @Id @GeneratedValue public Integer getEmpno() { return empno; } public void setEmpno(Integer empno) { this.empno = empno; } public String getEmpname() { return empname; } public void setEmpname(String empname) { this.empname = empname; } }
IdCard(身份证类):
package cn.happy.ontoondouble; import javax.persistence.*; /** * Created by CKW on 2017/2/16. */ @Entity @Table(name = "IDCARD1") public class IdCard { @Id @GeneratedValue private Integer iid; private String inum; @OneToOne(mappedBy = "idCard",cascade = CascadeType.ALL) private Emp emp; public Integer getIid() { return iid; } public void setIid(Integer iid) { this.iid = iid; } public String getInum() { return inum; } public void setInum(String inum) { this.inum = inum; } public Emp getEmp() { return emp; } public void setEmp(Emp emp) { this.emp = emp; } }
测试类:
package cn.happy.onetoeonedoubletest; import cn.happy.ontoondouble.Emp; import cn.happy.ontoondouble.IdCard; import org.hibernate.Session; import org.hibernate.SessionFactory; import org.hibernate.Transaction; import org.hibernate.cfg.Configuration; import org.junit.After; import org.junit.Before; import org.junit.Test; /** * Created by CKW on 2017/2/16. */ public class annTest { Configuration cfg; Session session; Transaction tx; @Before public void myBefore(){ //创建配置对象 cfg=new Configuration().configure("Hibernate2.cfg.xml"); // 2.根据配置对象创建SessionFactory SessionFactory factory=cfg.buildSessionFactory(); //3.根据SessionFactory去创建Session session= factory.getCurrentSession(); //3.5在Session创建后开启事务 xxx0001 xxxxx003 tx= session.beginTransaction(); } @After public void myAfter(){ //5.提交事务 tx.commit(); } @Test public void test1(){ Emp emp=new Emp(); emp.setEmpname("哈士奇"); IdCard idCard=new IdCard(); idCard.setInum("351579542612452163"); idCard.setEmp(emp); emp.setIdCard(idCard); session.save(idCard); } }
2.一对多双向
Dept(部门类):
package cn.happy.onetomanydouble; import javax.persistence.*; import java.util.HashSet; import java.util.Set; @Entity //@Cache(usage = CacheConcurrencyStrategy.NONSTRICT_READ_WRITE) @Table(name = "Dept2") /** * Created by CKW on 2017/2/16. */ public class Dept { @Id @GeneratedValue private Integer did; @Column private String dname; @OneToMany(mappedBy = "dept",cascade = CascadeType.ALL,fetch = FetchType.LAZY) //@Cache(usage = CacheConcurrencyStrategy.NONSTRICT_READ_WRITE) private Set<Emp> emps=new HashSet<Emp>(); public Integer getDid() { return did; } public void setDid(Integer did) { this.did = did; } public String getDname() { return dname; } public void setDname(String dname) { this.dname = dname; } public Set<Emp> getEmps() { return emps; } public void setEmps(Set<Emp> emps) { this.emps = emps; } }
Emp(员工类):
package cn.happy.onetomanydouble; import javax.persistence.*; @Entity @Table(name = "Emp2") /** * Created by CKW on 2017/2/16. */ public class Emp { @Id @GeneratedValue private Integer eid; @Column private String name; @ManyToOne @JoinColumn(name = "did") private Dept dept; public Integer getEid() { return eid; } public void setEid(Integer eid) { this.eid = eid; } public String getName() { return name; } public void setName(String name) { this.name = name; } public Dept getDept() { return dept; } public void setDept(Dept dept) { this.dept = dept; } }
测试类:
@Test public void test1(){ Emp emp=new Emp(); emp.setName("哈士奇"); Dept dept=new Dept(); dept.setDname("财务部"); dept.getEmps().add(emp); emp.setDept(dept); session.save(dept); }
3.多对多双向
Game(游戏类):
package cn.happy.manytomanydouble; import javax.persistence.*; import java.util.HashSet; import java.util.Set; @Entity @Table(name = "Game") /** * Created by CKW on 2017/2/16. */ public class Game { @Id @GeneratedValue(strategy = GenerationType.SEQUENCE,generator = "sql_Game") @SequenceGenerator(name = "sql_Game",sequenceName = "sql_Game",allocationSize = 1,initialValue = 1) private Integer gid; @Column private String gname; @ManyToMany(cascade = CascadeType.ALL) @JoinTable(name = "PG",joinColumns = {@JoinColumn(name = "gid")},inverseJoinColumns = {@JoinColumn(name = "pid")}) private Set<PlayerHome> playerHomes=new HashSet<PlayerHome>(); public Integer getGid() { return gid; } public void setGid(Integer gid) { this.gid = gid; } public String getGname() { return gname; } public void setGname(String gname) { this.gname = gname; } public Set<PlayerHome> getPlayerHomes() { return playerHomes; } public void setPlayerHomes(Set<PlayerHome> playerHomes) { this.playerHomes = playerHomes; } }
PlayerHOME(玩家类):
package cn.happy.manytomanydouble; import javax.persistence.*; import java.util.HashSet; import java.util.Set; @Entity @Table(name = "PlayerHome") /** * Created by CKW on 2017/2/16. */ public class PlayerHome { @Id @GeneratedValue(strategy = GenerationType.SEQUENCE,generator = "sql_PlayerHome") @SequenceGenerator(name = "sql_PlayerHome",sequenceName = "sql_PlayerHome",allocationSize = 1,initialValue = 1) private Integer pid; @Column private String pname; @ManyToMany(cascade = CascadeType.ALL,mappedBy = "playerHomes") private Set<Game> games=new HashSet<Game>(); public Integer getPid() { return pid; } public void setPid(Integer pid) { this.pid = pid; } public String getPname() { return pname; } public void setPname(String pname) { this.pname = pname; } public Set<Game> getGames() { return games; } public void setGames(Set<Game> games) { this.games = games; } }
测试类:
@Test public void myTest(){ PlayerHome playerHome=new PlayerHome(); playerHome.setPname("川"); PlayerHome playerHome1=new PlayerHome(); playerHome1.setPname("安"); Game game=new Game(); game.setGname("CS"); Game game1=new Game(); game1.setGname("CF"); playerHome.getGames().add(game); playerHome.getGames().add(game1); playerHome1.getGames().add(game); playerHome1.getGames().add(game1); game.getPlayerHomes().add(playerHome); game.getPlayerHomes().add(playerHome1); game1.getPlayerHomes().add(playerHome); game1.getPlayerHomes().add(playerHome1); session.save(game); session.save(game1); }