三种实现方式，已顾客与房间的关系为例：
0. DB代码：
??? DROP?TABLE?IF?EXISTS 'Customer';?
??? CREATE?TABLE 'Customer' (
??? 'id int ( 11 )?NOT?NULL?auto_increment,
? ? 'name' varchar(255 )?NOT?NULL,
? ? PRIMARY?KEY??(`id`))?ENGINE=InnoDB?DEFAULT?CHARSET=utf8;
?
??? DROP?TABLE?IF?EXISTS 'Room';?
??? CREATE?TABLE 'Room' (
??? 'id' int ( 11 )?NOT?NULL?auto_increment,??
??? 'name' varchar(255 )?NOT?NULL,??
??? 'customer_id' int ( 11 )?,
? ? foreign?key?(' customer _id')?references customer('id'),?
??? PRIMARY?KEY??('id') )?ENGINE=InnoDB?DEFAULT?CHARSET=utf8;?
1. 实体代码：
??? public ? class Customer implements ?java.io.Serializable?{?
????????????? private ?Integer?id;??
? ? ? ? ?? ?? private ?String?name;??
? ? ? ? ?? ?? private Room room;
????????????? //省略构造函数，get/set方法
??? }
??? public ? class Room implements ?java.io.Serializable?{?
????????????? private ?Integer?id;??
? ? ? ? ?? ?? private ?String?name;??
? ? ? ? ?? ?? private Customer customer ;
????????????? //省略构造函数，get/set方法
??? }
2. 通过外键方式实现：
??? Room.hbm.xml:
??? <hibernate-mapping>?
???????????? <class ?name= "com.domain.Customer" ?table= "Customer" ?catalog= "Temp" >
????????????????????? < id?name="id" ?type= "java.lang.Integer" >?
??????????????????????????? <column?name="id" ?/>
? ? ? ? ? ? ? ? ? ? ? ????? <generator?class = "native" ?/>
? ? ? ? ? ? ?? ?????? </id>??
? ? ? ? ? ? ? ? ????? <property?name="name" ?type= "java.lang.String>
???????????????????????????????? <column?name="name" ?not- null = "true" ?/>
? ? ? ? ? ? ?? ?????? </property>
????????????????????? <!--?class 可以不写，因为根据name的值computer(属性)，会通过反射自动找到属于哪个类的?-->
????????????????????? <one-to-one?cascade="all" ?name= "customer" ? class = "com.domain.Customer" ?
?????????????????????????????? property-ref= " customer " >
????????????????????? </one-to-one>
??????????????? </class >
???? </hibernate-mapping>?
???? Customer.hbm.xml:
???? <hibernate-mapping>
?????????? <class ?name= "com.domain.Customer" ?table= "Customer" ?catalog= "Temp" >
??????????????? <id?name="id" ?type= "java.lang.Integer" >
????????????????????? <column?name="id" ?/>
????????????????????? <generator?class = "native" ?/>
??????????????? </id>
??????????????? <property?name="name" ?type= "java.lang.String" >
????????????????????? <column?name="name" ?not- null = "true" ?/>
??????????????? </property>
??????????????? <!--?many开头的是代表该表持有外键?-->
??????????????? <many-to-one??name="rom" ? class = "com.domain.Room" ??unique= "true">
????????????????????? <column?name=" customer _id" ?/>
??????????????? </many-to-one>?
???????????? </class >
????? </hibernate-mapping>?
3. 通过主键方式，即一个表的主键有另一个表的主键决定，本例中Customer表的主键由Room表决定：
??? Room.hbm.xml:
??? <hibernate-mapping>?
???????????? <class ?name= "com.domain.Customer" ?table= "Customer" ?catalog= "Temp" >
????????????????????? < id?name="id" ?type= "java.lang.Integer" >?
??????????????????????????? <column?name="id" ?/>
? ? ? ? ? ? ? ? ? ? ? ????? <generator?class = "native" ?/>
? ? ? ? ? ? ?? ?????? </id>??
? ? ? ? ? ? ? ? ????? <property?name="name" ?type= "java.lang.String>
???????????????????????????????? <column?name="name" ?not- null = "true" ?/>
? ? ? ? ? ? ?? ?????? </property>
????????????????????? <!--?class 可以不写，因为根据name的值computer(属性)，会通过反射自动找到属于哪个类的?-->
????????????????????? <!--
????????????????????? <one-to-one?cascade="all" ?name= "customer" ? class = "com.domain.Customer" ?
?????????????????????????????? property-ref= " customer " >
????????????????????? </one-to-one>
????????????????????? -->
????????????????????? <one-to-one name="customer" class = "com.domain.Customer" cascade="all" >
??????????????? </class >
???? </hibernate-mapping>?
???? Customer.hbm.xml:
???? <hibernate-mapping>
?????????? <class ?name= "com.domain.Customer" ?table= "Customer" ?catalog= "Temp" >
??????????????? <id?name="id" ?type= "java.lang.Integer" >
????????????????????? <column?name="id" ?/>
????????????????????? <!--
????????????????????? <generator?class = "native" cascade="all" ? />
?????????????????????? -->
????????????????????? <!--Customer的主键由Room的主键决定，可以看成是外键--> ?????
????????????????????? <generator?class = "foreign" >
????????????????????????????? <param?name="property" >room</param>
????????????????????? </generator>
????????????????????? <!--或者使用下面的方式-->
????????????????????? <generator class="increment"></generator>
??????????????? </id> ???????????????
?
??????????????? <property?name="name" ?type= "java.lang.String" >
????????????????????? <column?name="name" ?not- null = "true" ?/>
??????????????? </property>
??????????????? <!--?many开头的是代表该表持有外键?-->
??????????????? <!--
??????????????? <many-to-one??name="rom" ? class = "com.domain.Room" ??unique= "true">
????????????????????? <column?name=" customer _id" ?/>
??????????????? </many-to-one>?
??????????????? -->
??????????????? <one-to-one name="rom" ? class = "com.domain.Room" />
??????????????? <!--或者使用下面的方式-->
??????????????? <one-to-one name="rom" ? class = "com.domain.Room" constrained="true" />
???????????? </class >
????? </hibernate-mapping>?
4. 通过关系表实现：
??? create?table room_cust(?
????????????? room_id?int ?not? null ,??
? ? ? ? ?? ?? cust_id?int ?not? null
??? )ENGINE=InnoDB?DEFAULT?CHARSET=utf8;?
??? 配置文件：
??? <!--optional= "true" 的意思是只有当room_id?和?cust_id?都不为空时才在关系表里插入。这样也会插入 2 遍，
?????? 所以需要inverse= "true" 把一方设置为虚的。即不让插入到关系表中-->
??? <join?table=" room_cus t" ?optional= "true" ?inverse= "true" >
????????????? <key?column="cust_id" />
????????????? <many-to-one?name="room" ?column= "room_id" ?unique= "true" />
??? </join>?
?
?