Hibernate映射一对一关联关系

                                                                                映射一对一关联

Hibernate提供了两种映射一对一关联关系的方式，分别是按照外键映射和按照主键映射。

下面是员工表和档案信息表（员工和档案表之间的关系是一对一的关系）

　　 档案表（dept）

public class Dept {
    private Integer deptid;
    private String mystreet;
    private Emp emp;
            
    public Dept() {
    }
    
    public Dept(Integer deptid, String mystreet, Emp emp) {
        this.deptid = deptid;
        this.mystreet = mystreet;
        this.emp = emp;
    }
    public Integer getDeptid() {
        return deptid;
    }
    public void setDeptid(Integer deptid) {
        this.deptid = deptid;
    }
    public String getMystreet() {
        return mystreet;
    }
    public void setMystreet(String mystreet) {
        this.mystreet = mystreet;
    }
    public Emp getEmp() {
        return emp;
    }
    public void setEmp(Emp emp) {
        this.emp = emp;
    }
    
}

      员工表（emp）

public class Emp {
    private Integer empid;
    private String myname;
    private Dept dept;

    public Emp() {
    }
    
    public Emp(Integer empid, String myname, Dept dept) {
        this.empid = empid;
        this.myname = myname;
        this.dept = dept;
    }
    public Integer getEmpid() {
        return empid;
    }
    public void setEmpid(Integer empid) {
        this.empid = empid;
    }
    public String getMyname() {
        return myname;
    }
    public void setMyname(String myname) {
        this.myname = myname;
    }
    public Dept getDept() {
        return dept;
    }
    public void setDept(Dept dept) {
        this.dept = dept;
    }
}

下面是第一种方案是按照主键映射

  Emp的配置文件

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC 
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
    <hibernate-mapping package="cn.rm.onetoone_pk">
        <class name="Emp" table="EMP2016">
            <id name="empid" column="EMPID" type="int">
                <generator class="sequence">
                    <param name="sequence">sq_id</param>
                </generator>
            </id>
            <property name="myname" column="MYNAME" type="string"></property>
            <one-to-one name="dept" class="Dept" property-ref="emp"></one-to-one>
            <!-- property-ref为emp表明了Dept的emp属性建立了从Emp对象到Dept对象的关联  -->
        </class>
        
    </hibernate-mapping>

  Dept的配置文件

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC 
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
    <hibernate-mapping package="cn.rm.onetoone_pk">
        <class name="Dept" table="DEPT2016">
            <id name="deptid" column="DEPTID" type="int">
                <generator class="sequence">
                    <param name="sequence">hb_ids</param>
                </generator>
            </id>
            <property name="mystreet" column="MYSTREET" type="string"></property>
            <many-to-one name="emp" class="Emp" cascade="all" unique="true" column="RESUSERID"></many-to-one>
            <!-- cascade属性为all表示对本表的增 删 改 相关联的表都会自动更新 unique， 属性为true 表示唯一约束  column="RESUSERID" dept表的公共列-->
        </class>
    </hibernate-mapping>

这种方案的特点是：会在Dept表中增加一列 column="RESUSERID"这里就是与Emp相关联的列

第二种方案是按照外键映射

  Emp的配置文件

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC 
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
    <hibernate-mapping package="cn.rm.onetoone_fk">
        <class name="Emp" table="EMP2016fk">
            <id name="empid" column="EMPID" type="int">
                <generator class="foreign">
                    <param name="property">dept</param>
                </generator>
            </id>
            <property name="myname" column="MYNAME" type="string"></property>
            <one-to-one name="dept" class="Dept" constrained="true"></one-to-one>
            <!--  constrained="true" 表示Emp表中的主键同时作为外键参照Emp表中的主键 -->
        </class>      
    </hibernate-mapping>

  Dept的配置文件

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC 
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
    <hibernate-mapping package="cn.rm.onetoone_fk">
        <class name="Dept" table="DEPT2016fk">
            <id name="deptid" column="DEPTID" type="int">
                <generator class="sequence">
                    <param name="sequence">hb_ids</param>
                </generator>
            </id>
            <property name="mystreet" column="MYSTREET" type="string"></property>
            <one-to-one name="emp" class="Emp" cascade="all" ></one-to-one>
        </class>
    </hibernate-mapping>

这种方案的特点是员工表的主键和Dept表中的主键是相同的也就是Emp表和Dept表共享同一个OID