1 关联关系映射

多对一（Employee-Department）一对多（Department-Employee）一对一（Person-IdCard）多对多（teacher-student）cascade（Employee-Department）

2 多对一（Employee-Department）

**domain文件：**Studcourse.java

public class Studcourse { private BigDecimal stucourseid; private Student student; private Course course; private BigDecimal grade; }

**配置文件：**Studcourse.hbm.xml

<many-to-one name="student" class="com.test.domain.Student" fetch="select"> <column name="SID" precision="22" scale="0" /> </many-to-one>

3 一对多（Department-Employee）

**domain文件：**Student.java

public class Student implements java.io.Serializable { private BigDecimal sid; private String sname; private Set studcourses = new HashSet(0); }

**配置文件：**Student.hbm.xml

<set name="studcourses" inverse="true"> <key> <column name="SID" precision="22" scale="0" /> </key> <one-to-many class="com.test.domain.Studcourse" /> </set>

4 一对一（Person-IdCard）

有两种方式：基于主键的一对一；基于外键的一对一。

①基于主键的一对一

**domain文件：**Person.java和IdCard.java

class Person{ private Integer id; private String name; private IdCard idCard; } class IdCard { private Integer id; private Date validateDte; private Person person; }

配置文件： Person.hbm.xml

<one-to-one name="idCard" class="com.test.domain.IdCard"></one-to-one>

IdCard.hbm.xml

<id name="id" type="java.lang.Integer"> <generator class="foreign"> <param name="property">person</param> </generator> </id> <one-to-one name="person" class="com.test.domain.Person" constrained="true"></one-to-one>

②基于外键的一对一

**domain文件：**Person.java和IdCard.java

class Person{ private Integer id; private String name; private IdCard idCard; } class IdCard { private Integer id; private Date validateDte; private Person person; }

配置文件： Person.hbm.xml

<one-to-one name="idCard" class="com.test.domain.IdCard"></one-to-one>

IdCard.hbm.xml

<id name="id" type="java.lang.Integer"> <generator class="assigned" /> </id> // one-to-one实际上是many-to-one的一个特例 <many-to-one name="person" unique="true" />

5 多对多（teacher-student）

在操作和性能方面都不太理想，所以多对多的映射使用较少，实际使用中最好转换成一对多的对象模型；Hibernate会为我们创建中间关联表，转换成两个一对多。 domain文件：

public class Student implements java.io.Serializable { private BigDecimal sid; private String sname; private Set studcourses = new HashSet(0); } public class Course implements java.io.Serializable { private BigDecimal cid; private String cname; private Short ccredit; private Set studcourses = new HashSet(0); } public class Studcourse { private BigDecimal stucourseid; private Student student; private Course course; private BigDecimal grade; }

配置文件： Student.hbm.xml 和 Course.hbm.xml

<set name="studcourses" inverse="true"> <key> <column name="S_ID" precision="22" scale="0" /> </key> <one-to-many class="com.test.domain.Studcourse" /> </set>

Studcourse.hbm.xml

<many-to-one name="student" class="com.test.domain.Student" fetch="select"> <column name="S_ID" precision="22" scale="0" /> </many-to-one> <many-to-one name="course" class="com.test.domain.Course" fetch="select"> <column name="C_ID" precision="22" scale="0" /> </many-to-one>

6 cascade（Employee-Department）

Cascade用来说明当对主对象进行某种操作（添加、修改、删除……）时(比如删除一个部门时，删除该部门所有员工)，是否对其关联的从对象也作类似的操作。常用的cascade： none, all, save-update, delete, lock, refresh, evict, replicate, persist, merge, delete-orphan(one-to-many)一般在many-to-one，many-to-many中不设置级联，在one-to-one， one-to-many中设置级联。在集合属性和普通属性中都能使用cascade一般讲，cascade配置在one-to-one（主对象一方）， one-to-many（one的一方） <set name="studcourses" inverse="true" cascade="all"> <key> <column name="SID" precision="22" scale="0" /> </key> <one-to-many class="com.test.domain.Studcourse" /> </set>