怎么理解ejb的关系映射？

Question

开发工具jbuilderX，服务器weblogic 8.1,数据库是interbase

Answer 1

使用CMR，可以通过“在部署描述符文件中描述＋在代码中写声明（不写实现）”
的方式管理表关系.

Answer 2

这些声明是不是会出现在ejb的localremote接口中？
那我建立一个ejb的实例时那个关联字段我该怎么处理，用自己手工设置值？那跟不设关联也没有什么区别啊。
能不能说一下设置了关系后有什么作用啊？

Answer 3

是这样的,我举个例子吧:1:N=========================================
    CompanyPK   |   Name                |
=========================================
    12345       |The Middleware Company |
==============================================================================================
    EmployeePK  |   Name    |   Sex |   Company     |
=====================================================
    20202       |   Ed      |   M   |   12345       |
    20203       |   Floyd   |   M   |   12345       |
=====================================================
用BMP实现1:N关系public class CompanyBean implements EntityBean
{
    private String companyPK;
    private String companyName;
    private Vector employees;
    
    public Collection getEmployees()
    {
        return this.employees;
    }
    
    public void setEmployees(Collection e)
    {
        this.employees = (Vector) e;
    }
    
    public void ejbLoad()
    {
        // 1. 利用SQL选择Company
        // 2. JNDI查找EmployeeHome
        // 3. 调用EmployeeHome.findByCompany(companyPk)
    }
    
    public void ejbStore()
    {
        // 利用SQL更新compnay
    }
}用CMP实现1:N关系public abstract CompanyBean implements EntityBean
{
    public abstract Collection getEmployees();
    public abstract void setEmployees(Collection e);
    
    public void ejbLoad();
    public void ejbStore();
}ejb-jar.xml
<ejb-jar>
    <enterprise-beans>
    ....
    </enterprise-beans>
    
    <relationships>
        <ejb-relation>
            <ejb-relation-name>Company-Employees</ejb-relation-name>
            <ejb-relation-role>
                <ejb-relation-role-name>
                    Company-Employs-Employees
                </ejb-relation-role-name>
                
                <multiplicity>One</multiplicity>
                
                <relationship-role-source>
                    <ejb-name>Company</ejb-name>
                </relationship-role-source>
                
                <cmr-field>
                    <cmr-field-name>employees</cmr-field-name>
                    <cmr-field-type>java.util.Collections</cmr-field-type>
                </cmr-field>
            </ejb-relation-role>
            
            <ejb-relation-role>
                <ejb-relation-role-name>
                    Employees-WorkAt-Company
                </ejb-relation-roel-name>
                
                <multiplicity>Many</multiplicity>
                
                <relation-role-source>
                    <ejb-name>Employee</ejb-name>
                </relation-role-source>
            </ejb-relation-role>
        </ejb-relation>
    </relationships>    
</ejb-jar>在CMP实现中,不用手动进行设置,完全有容器来做.