由于一对多，和多对一的双向关联映射基本上一样，所以这里就一起写下来！
Annotations配置
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@Entity
@Table
(name=
"t_group"
)
publicclass Group {
private
Integer id;
private
String name;
private
Set<Person> persons=newHashSet<Person>();
//set不允许重复，最适合数据库模型
@Id
@GeneratedValue
public
Integer getId() {
returnid;
}
publicvoid setId(Integerid) {
this
.id = id;
}
@Column
(name=
"t_name"
)
public
String getName() {
returnname;
}
publicvoid setName(Stringname) {
this
.name = name;
}
@OneToMany
(mappedBy=
"group"
)
//意识是告诉Hibernate的关联关系应该设在Person，多的一方
// 只有OneToOne,OneToMany,ManyToMany上才有mappedBy属性，ManyToOne不存在该属性；
public
Set<Person>getPersons() {
returnpersons;
}
publicvoidsetPersons(Set<Person> persons) {
this
.persons = persons;
}
}
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@Entity
@Table
(name=
"t_person"
)
publicclass Person {
private
Integer id;
private
String name;
private
Integer age;
private
Group group;
@ManyToOne
public
Group getGroup() {
returngroup;
}
publicvoid setGroup(Groupgroup) {
this
.group = group;
}
@Id
@GeneratedValue
public
Integer getId() {
returnid;
}
publicvoid setId(Integerid) {
this
.id = id;
}
@Column
(name=
"p_name"
)
public
String getName() {
returnname;
}
publicvoid setName(Stringname) {
this
.name = name;
}
@Column
(name=
"p_age"
)
public
Integer getAge() {
returnage;
}
publicvoid setAge(Integerage) {
this
.age = age;
}
}
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XML配置
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<?xml version=
"1.0"
?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"
>
<hibernate-mapping
package
=
"csg.hibernate.entity"
>
<
class
name=
"Group"
table=
"t_group"
>
<id name=
"id"
>
<column name=
"id"
/>
<generator
class
=
"native"
/>
</id>
<property name=
"name"
/>
<set name=
"persons"
>
<key column=
"groupId"
/>
<one-to-many
class
=
"csg.hibernate.entity.Person"
/>
</set>
</
class
>
</hibernate-mapping>
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<?
xml
version
=
"1.0"
?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<
hibernate-mapping
package
=
"csg.hibernate.entity"
>
<
class
name
=
"Person"
table
=
"t_person"
>
<
id
name
=
"id"
>
<
column
name
=
"id"
/>
<
generator
class
=
"native"
/>
</
id
>
<
property
name
=
"name"
/>
<
property
name
=
"age"
/>
<
many-to-one
name
=
"group"
column
=
"groupId"
/>
</
class
>
</
hibernate-mapping
>
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由上大家都可以得出疑问？
为什么双向关联在Group中key需要指定column而在Person中也需要指定column呢？
如果其中一个不指定会有什么后果？
如果指定的column不一致又会有什么后果？
大家可以试一下！
本文转自 小夜的传说 51CTO博客，原文链接：http://blog.51cto.com/1936625305/1568892，如需转载请自行联系原作者
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