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【hibernate】之关于一对一单向，双向关联映射

时间：2014-11-26 02:13:28      阅读：379      评论：0      收藏：0      [点我收藏+]

首先我们来看，Hibernate官方对于一对一单向关联的解释:

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基于外键关联的单向一对一关联和单向多对一关联几乎是一样的。唯一的不同就是单向一对一关

联中的外键字段具有唯一性约束。

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ok,那我们也可以这样理解，一对一其实就是多对一关联的特殊形式，我们知道Hibernate的配置方式有两种，分别是Annotations，XML两种配置方式！

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Annotations的一对一单向关联映射

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人(User)和***号(Card)

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@Entity
@Table(name="t_user")
publicclass?User?{
????private?Integer?id;
????private?String?name;
????private?Card?card;
?????
????@OneToOne
????@JoinColumn(name="card_id",unique=true)//name是自定义关联外键的列名
????public?Card?getCard()?{
???????returncard;
????}
????publicvoid?setCard(Card?card)?{
???????this.card?=?card;
????}
????@Id
????@GeneratedValue
????public?Integer?getId()?{
???????returnid;
????}
????publicvoid?setId(Integerid)?{
???????this.id?=?id;
????}
?????
????@Column(name="name")
????public?String?getName()?{
???????returnname;
????}
????publicvoid?setName(Stringname)?{
???????this.name?=?name;
????}
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@Entity
@Table(name="t_card")
publicclass?Card?{
????private?Integer?id;
????private?String?num;
?????
????@Id
????@GeneratedValue
????public?Integer?getId()?{
???????returnid;
????}
????publicvoid?setId(Integerid)?{
???????this.id?=?id;
????}
????@Column(name="card_id")
????public?String?getNum()?{
???????returnnum;
????}
????publicvoid?setNum(Stringnum)?{
???????this.num?=?num;
????}
}


XML一对一单向关联

Person和Group，一个人只能在一个组

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publicclass?Group?{
????private?Integer?id;
????private?String?name;
????public?Integer?getId()?{
???????returnid;
????}
????publicvoid?setId(Integerid)?{
???????this.id?=?id;
????}
????public?String?getName()?{
???????returnname;
????}
????publicvoid?setName(Stringname)?{
???????this.name?=?name;
????}
}
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publicclass?Person?{
????private?Integer?id;
????private?String?name;
????private?Integer?age;
????private?Group?group;
????public?Group?getGroup()?{
???????returngroup;
????}
????publicvoid?setGroup(Groupgroup)?{
???????this.group?=?group;
????}
????public?Integer?getId()?{
???????returnid;
????}
????publicvoid?setId(Integerid)?{
???????this.id?=?id;
????}
????public?String?getName()?{
???????return?name;
????}
????public?void?setName(Stringname)?{
???????this.name?=?name;
????}
????public?Integer?getAge()?{
???????return?age;
????}
????publicvoid?setAge(Integer?age){
???????this.age?=?age;
????}
}
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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"?/>
????</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="group_id"?unique="true"?not-null="true"?/>
????</class>
</hibernate-mapping>

Ok,到这里，大家就有点疑惑，为什么我们的Annotaions配置采用的是one-to-one而我们的xml配置采用的是many-to-one呢？

当然XML配置是我参考Hibernate的文档而来，因为一对一本身就是多对一的特殊形式，

但是配置many-to-one又给我们一种暗示，多个***号对应一个人，所以Hibernate根据这种情况提供unique唯一性来确认!

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Annotations一对一双向关联映射

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User和Card

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@Entity
@Table(name="t_user")
publicclass?User?{
????private?Integer?id;
????private?String?name;
????private?Card?card;
????@OneToOne
????@JoinColumn(name="card_id",unique=true)//name主要是自定义关联外键的列名
????public?Card?getCard()?{
???????returncard;
????}
????publicvoid?setCard(Cardcard)?{
???????this.card?=?card;
????}
????@Id
????@GeneratedValue
????public?Integer?getId()?{
???????returnid;
????}
????publicvoid?setId(Integerid)?{
???????this.id?=?id;
????}
????@Column(name="name")
????public?String?getName()?{
???????returnname;
????}
????publicvoid?setName(Stringname)?{
???????this.name?=?name;
????}
}
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@Entity
@Table(name="t_card")
publicclass?Card?{
????private?Integer?id;
????private?String?num;
????private?User?user;
?????
????@OneToOne(mappedBy="card")//mappedBy的意思是指定User中的card作为关联外键，否则User和Card都会出现外键
????public?User?getUser()?{
???????returnuser;
????}
????publicvoid?setUser(Useruser)?{
???????this.user?=?user;
????}
????@Id
????@GeneratedValue
????public?Integer?getId()?{
???????returnid;
????}
????publicvoid?setId(Integerid)?{
???????this.id?=?id;
????}
????@Column(name="card_id")
????public?String?getNum()?{
???????returnnum;
????}
????publicvoid?setNum(Stringnum)?{
???????this.num?=?num;
????}
}

?

Ok？那么我们可以看到在Annotaions中的配置都是ont-to-one，那么我们在xml中的配置呢？

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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="group_id"?unique="true"?not-null="true"?/>
????</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="Group"?table="t_group">
???????<id?name="id">
???????????<column?name="id"/>
???????????<generator?class="native"?/>
???????</id>
???????<property?name="name"?/>
???????<!--?many-to-one这种配置会分别在两个表中都产生外键，造成数据的多余，通常我们采用one-to-one的形式在xml中配置?-->
???????<many-to-one?name="Person"?column="person_id"?unique="true"?/>
????<!--???<one-to-onename="person"property-ref="group"/>?-->
????</class>
</hibernate-mapping>

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ok，到这里一对一的单双向关联映射基本上就是这样，随笔之作，有问题，请留言！

【hibernate】之关于一对一单向，双向关联映射

原文：http://jlins.iteye.com/blog/2160463
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