【Hibernate】之关于一对多，多对一双向关联映射
因为一对多。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
@Entity
@Table(name="t_group")
publicclass Group {
private Integer id;
private String name;
private Set<Person> persons=newHashSet<Person>();//set不同意反复，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
// 仅仅有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;
}
}
@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;
}
}
XML配置
<?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>
<?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>
由上大家都能够得出疑问？
为什么双向关联在Group中key须要指定column而在Person中也须要指定column呢？
假设当中一个不指定会有什么后果？
假设指定的column不一致又会有什么后果？
大家能够试一下！
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