2009.11.23(2)——Hibernate(4) Annotations注解之一对多

2009.11.23(2)——Hibernate(4) Annotations注解之一对多
今天是想学习下hql的连接语句，要学习什么内连接，外连接，就需要在数据库中构造下环境，只好在数据库中建立了company和employee的一对多数据库,如下

create table company
  (cid number(7) primary key,
  cname varchar2(15) not null
  );

create table employee
(eid number(7) primary key,
ename varchar2(15) not null,
age number(3),
c_id number(7) references company(cid)
)

插入数据：

insert into company values(1,'huitu');
 
insert into company values(2,'ruitong');
 
insert into company values(3,'jinshui');
 
insert into company values(4,'nantian');

insert into company values(5,'lianxiang');

insert into employee values(1,'weixiangliang',23,1);
 
insert into employee values(2,'dengzexia',21,1);

insert into employee values(3,'xiezhongchi',25,1);

insert into employee values(4,'huangzhong',22,2);
 
insert into employee values(5,'wangyuwen',21,2);
 
insert into employee values(6,'jiayupeng',24,3);
 
insert into employee values(7,'liumin',26,3);
 
insert into employee values(8,'dingneng',23,4);
 
insert into employee values(9,'xiaoqiu',25,4);

insert into employee(eid,ename,age) values(10,'sky',25);

然后写这两张表对应的pojo类，但是这时就又用到Annotation了，
Company.java

@Entity
@Table(name="Company")
public class Company {
	
	private Integer cid;
	private String cname;
	private Set<Employee> employees = new HashSet<Employee>() ;
	@Id
	public Integer getCid() {
		return cid;
	}
。。。。。。。。。
@OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY, mappedBy = "company") 
	public Set<Employee> getEmployees() {
		return employees;
	}

这个是OntToMany()，mappedBy，是相对应的外键，刚开始我写的是c_id，我以为这个不就是外键嘛，不过一直报错，后来我想可能是Employees的外键对应的表，就写了个company,居然对了 ，不过我还不是很理解。我查了下资料知道了，mappedBy后面跟的应该是@ManyToOne所标示的属性
Employee.java

@Entity
@Table(name="Employee")
public class Employee {
	
	private Integer eid;
	private String ename;
	private Integer age;
	private Company company;
	@Id
	public Integer getEid() {
		return eid;
	}
。。。。。。。。。。。。。。。。
@ManyToOne()
	@JoinColumn(name="c_id",referencedColumnName="cid")
	public Company getCompany() {
		return company;
	}

对了 这里要提下单向和双向的区别：
如果是双向的话：
1.要在company加上mappedBy
2.要在Employee加上manyToOne
单向的话，只需要OneToMany就行了
这个 参考 http://dennnis-zane.blog.sohu.com/12210434.html

对了 差点忘了 还要在spring的配置文件

<bean id="sessionFactory"  
        class="org.springframework.orm.hibernate3.annotation.AnnotationSessionFactoryBean">   
        <property name="dataSource" ref="dataSource" />   
        <property name="annotatedClasses">   
            <list>   
                <value>com.huitu.khms.pojo.Company</value>
                <value>com.huitu.khms.pojo.Employee</value>   
            </list>   
        </property>
。。。。。