Hibernate中各种关联关系配置

一、单向多对一

　　举例：多个订单对应一个顾客

　　顾客类Customer.java：

public class Customer{
    private Integer customerId;
    private String customerName;
//get() set() 省略
}

　　订单类Order.java：

public class Order {
    private Integer orderId;
    private String orderName;

    private Customer customer;

    /**
    geter、seter   此处省略
   **/
}    

　　Customer.hbm.xml:

<class name="Customer" table="Customer">
    <id name="customerId" column="COSTOMER_ID" type="integer">
　　　　<generator class="native"/><!-- 主键生成策略native 不同数据库不同 -->
　　</id>
　　<property name="customerName" column="CUSTOMER_NAME" type="string"></property>
</class>

　　Order.hbm.xml:

<class name="Order" table="order">
    <id name="orderId" column="ORDER_ID" type="integer">
            <generator class="native"/>
    </id>
　　<property name="orderName" column="ORDER_NAME" type="string"></property>
　　<!-- 映射多对一关系 -->
　　<many-to-one name="customer" class="Customer" column="CUSTOMER_ID"></many-to-one>
</class>

二、双向多对一

　　顾客类 Customer.java:

public class Customer{
    private Integer customerId;
    private String customerName;
//增加Set类型属性 并初始化空的Set
    private Set<Order> orders = new HashSet<Order>();

//get() set() 省略
}

　　订单类Order.java

public class Order {
    private Integer orderId;
    private String orderName;

    private Customer customer;

    /**
    geter、seter   此处省略
   **/
}    

　　Customer.hbm.xml

<class name="Customer" table="Customer">
    <id name="customerId" column="COSTOMER_ID" type="integer">
　　　　<generator class="native"/>
　　</id>
　　<property name="customerName" column="CUSTOMER_NAME" type="string"></property>
　　<set name="orders" table="order"  inverse="true"><!-- inverse设为true放弃维护关联关系 ， 又另一端单独维护 -->
  　　  <key column="CUSTOMER_ID"></key><!-- 指定外键字段 -->
　　　　<one-to-many class="Order"/>
　　</set>
</class>

　　Order.hbm.xml

<class name="Order" table="order">
    <id name="orderId" column="ORDER_ID" type="integer">
            <generator class="native"/>
    </id>
　　<property name="orderName" column="ORDER_NAME" type="string"></property>
　　<!-- 映射多对一关系 -->
　　<many-to-one name="customer" class="Customer" column="CUSTOMER_ID"></many-to-one>
</class>

三、单向一对一

　　举例：一个部门Department 一个经理Manager

　　实体类：Department.java

public class Department{
    private Integer departmentId;
    private String departmentName;
    private Manager manager;
//省略geter seter;
}

　　　Manager.java

public class Manager{
    private Integer managerId;
    private String managerName;
//省略geter，seter；
}

　　1)基于外键的单向一对一：Department.hbm.xml

<class name="Department" table="DEPARTMENTS" >
        <id name="departmentId" column="DEPARTMENT_ID">
            <generator class="native" />
        </id>
        <property name="departmentName" column="DEPARTMENT_NAME" type="string">
        </property>
        <!-- 使用many-to-one 映射一对一， 一对一是一种特殊的多对一 -->
        <many-to-one name="manager" class="Manager" cascade="all" column="MANAGER_ID" unique="true"></many-to-one>
    </class>

　　2）基于主键的单向1对1

<class name="Department" table="DEPARTMENTS" >
        <id name="departmentId" column="DEPARTMENT_ID">
            <generator class="foreign">
                <param name="property">manager</param>
            </generator>

        </id>
        <property name="departmentName" column="DEPARTMENT_NAME" type="string">
        </property>
        <one-to-one name="manager" class="Manager" cascade="all" constrained="true"></one-to-one>
    </class>
<!-- one-to-one的单向关联中，如果constrained=false，则会在查询时就全部取出来，用left outer join的方式。如果constrained=true，hibernate即会延迟加载sql，只把主表的查出来，等有用到关联表的再发sql取。 -->

四、双向一对一

　　1）基于外键的双向一对一

　　Department.java:

public class Department{
    private Integer departmentId;
    private String departmentName;
    private Manager Manager;
}

　　Manager.java:

public class Manager{
    private Integer managerId;
    private String managerName;
    private Department department;
}

　　Department.hbm.xml:

<class name="Department" table="departments">
  <id name="departmentId" column="DEPARTMENT_ID" type="integer">
            <generator class="native" />
  </id>
  <property name="departmentName" column="DEPARTMENT_NAME" type="string">
   </property>
　　<many-to-one name="manager" column="MANAGER_ID" class="Manager" unique="true"/>
</class>

　　Manager.hbm.xml:

    <class name="Manager" table="MANAGERS">
        <id name="managerId" column="MANAGER_ID" type="integer">
            <generator class="native" />
        </id>
        <property name="managerName" column="MANAGER_NAME" type="string">
        </property>
        <!--  没有外键的一端，使用one-to-one进行映射，并指定property-ref属性为关联实体外键所对应的属性-->
        <one-to-one name="department"  class="Department" property-ref="manager"></one-to-one>
    </class>

　　2)基于主键的双向一对一：

　　Department.hbm.xml:

<class name="Department" table="departments">
  <id name="departmentId" column="DEPARTMENT_ID" type="integer">
            <generator class="foreign">
　　　　　　　　<param name="property">manager</param>
　　　　　　</generator>
  </id>
  <property name="departmentName" column="DEPARTMENT_NAME" type="string">
   </property>
　<one-to-one name="manager" class="Manager" constrained="true"/>
</class>

　　Manager.hbm.xml:

<class name="Manager" table="MANAGERS">
        <id name="managerId" column="MANAGER_ID" type="integer">
            <generator class="native" />
        </id>
        <property name="managerName" column="MANAGER_NAME" type="string">
        </property>
        <one-to-one name="department" class="Department" ></one-to-one>
 </class>

五、单向多对多

多对多需要一个中间表

Category.java

public class Category {
    private Integer id;
    private String name;

    private Set<Item> items = new HashSet<Item>();
}

Item.java

public class Item {
    private Integer id;
    private String name;
}

Category.hbm.xml

<class name="Category" table="CATEGORYS">
        <id name="id" column="CATEGORY_ID" type="integer">
            <generator class="native"></generator>
        </id>
        <property name="name" column="CATEGORY_NAME" type="string"></property>

        <set cascade="all" name="items" table="CATEGORYS_ITEMS"><!--中间表的名字-->
            <key column="CATEGORY_ID"></key>
            <many-to-many class="Item" column="ITEM_ID"></many-to-many>

        </set>
    </class>

Item.hbm.xml

<class name="Item" table="ITEMS" >
        <id name="id" column="ITEM_ID">
            <generator class="native" />
        </id>
        <property name="name" column="ITEM_NAME" type="string">
        </property>
    </class>

六、双向多对多

Category.java

public class Category {
    private Integer id;
    private String name;

    private Set<Item> items = new HashSet<Item>();
}

Item.java

public class Item {
    private Integer id;
    private String name;
    private Set<Category> categorys = new HashSet<Category>();
}

Category.hbm.xml

<class name="Category" table="CATEGORYS">
        <id name="id" column="CATEGORY_ID" type="integer">
            <generator class="native"></generator>
        </id>
        <property name="name" column="CATEGORY_NAME" type="string"></property>

        <set cascade="all" name="items" table="CATEGORYS_ITEMS"><!--中间表的名字-->
            <key column="CATEGORY_ID"></key>
            <many-to-many class="Item" column="ITEM_ID"></many-to-many>

        </set>
    </class>

Item.hbm.xml

<class name="Item" table="ITEMS" >
        <id name="id" column="ITEM_ID">
            <generator class="native" />
        </id>
        <property name="name" column="ITEM_NAME" type="string">
        </property>

        <set name="categorys" table="CATEGORYS_ITEMS" inverse="true"><!-- 必须有一端必须设置inverse -->
            <key column="ITEM_ID"></key>
            <many-to-many class="Category"  column="CATEGORY_ID"></many-to-many>
        </set>
    </class>

参考：尚硅谷Hibernate教程 http://www.atguigu.com/download.shtml