Hibernate的双向关系映射

一、双向1-N的关系映射
对于1-N的关联，Hibernate推荐使用双向关联，但不用1的一端来控制关联关系，而使用N
的一端来控制关联关系。N的一端直接访问关联类属性；1的一端增加集合属性的访问。
看下面2个POJO
public class Person implements Serializable
...{
    private int personid;
    priavte String name;
    private int age;
    private Set addresses = new HashSet();
    ……
}
public class Address implements Serializable
...{
    private int addressid;
    private String addressdetail;
    private Person person;
    public Address() ...{}
    public Address(Sring addressdetail) ...{
        this.addressdetail = addressdetail;
    }
}

1.无连接表的双向1-N关联
两个持久化类的配置文件都需要指定外键列的列名
xml version="1.0"?>
DOCTYPE hibernate-mapping
    PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "">
<hibernate-mapping package="prolove">
    <class name="Address">
        <id name="addressid">
            <generator class="identity"/>
        id>
        <property name="addressdetail"/>
        
        <many-to-one name="person" column="personid"/>
    class>
    <class name="Person">
        <id name="personid">
            <generator class="identity"/>
        id>
        <property name="name"/>
        <property name="age"/>

        <set name="addresss">
            <key column="personid"/>
            <one-to-many class="Address"/>
        set>
    class>
hibernate-mapping>

2.有连接表的双向1-N关联
两边确定连接表的table属性值应该相同，且不能省略。
xml version="1.0"?>
DOCTYPE hibernate-mapping
    PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "">
<hibernate-mapping package="prolove">
    <class name="Address">
        <id name="addressid">
            <generator class="identity"/>
        id>
        <property name="addressdetail"/>
        
        <join table="PersonAddress" inverse="true" optional="true">
            <key column="addressid"/>
            <many-to-one name="person" column="personid" not-null="true"/>
        join>
    class>
    <class name="Person">
        <id name="personid">
            <generator class="identity"/>
        id>
        <property name="name"/>
        <property name="age"/>
        
        <set name="addresses" table="PersonAddress">
            <key column="personid"/>
            
            <one-to-many column="addressid" unique="true" class="Address"/>
        set>
    class>
hibernate-mapping>

二、双向N-N关联
public class Person
...{
    private int personid;
    private String name;
    private int age;
    private Set addresses = new HashSet();
    ……
}
public class Address
...{
    private int addressid;
    private String addressdetail;
    private Set persons = new HashSet();
    public Address() ...{}
    public Address(String addressdetail) ...{
        this.addressdetail = addressdetail;
    }
}

xml version="1.0"?>
DOCTYPE hibernate-mapping
    PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "">
<hibernate-mapping package="prolove">
    <class name="Address">
        <id name="addressid">
            <generator class="identity"/>
        id>
        <property name="addressdetail"/>
        
        <set name="persons" inverse="true" table="jointable">
            
            <key column="addressid"/>
            
            <many-to-many column="personid" class="Person"/>
        set>
    class>
    <class name="Person">
        <id name="personid">
            <generator class="identity"/>
        id>
        <property name="name"/>
        <property name="age"/>
        
        <set name="addresses" table="jointable">
            <key column="personid"/>
            <many-to-many column="addressid" class="Address"/>
        set>
    class>
hibernate-mapping>

三、双向1-1关联
public class Person
...{
    //基本属性
    private int personid;
    private String name;
    private int age;
    //关联属性
    private Address address;
    ……
}
public class Address implements Serializable
...{
    private int addressid;
    private String addressdetail;
    private Person person;
    public Address() ...{}
    public Address(String addressdetail) ...{
        this.addressdetail = addressdetail;
    }
    ……
}

1.基于外键的双向1-1关联
xml version="1.0"?>
DOCTYPE hibernate-mapping
    PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "">
<hibernate-mapping package="prolove">
    <class name="Person">
        <id name="personid">
            <generator class="identity"/>
        id>
        <property name="name"/>
        <property name="age"/>
        
        <one-to-one name="address" property-ref="person"/>
    class>
    <class name="Address">
        <id name="addressid">
            <generator class="identity"/>
        id>
        <property name="addressdetail"/>
        
        <many-to-one name="person" unique="true"/>
    class>
hibernate-mapping>

2.基于主键的双向1-1关联
xml version="1.0"?>
DOCTYPE hibernate-mapping
    PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "">
<hibernate-mapping package="prolove">
    <class name="Person">
        <id name="personid">
            <generator class="identity"/>
        id>
        <property name="name"/>
        <property name="age"/>
        
        <one-to-one name="address"/>
    class>
    <class name="Address">
        <id name="addressid">
            <generator class="foreign">
                
                <param name="property">personparam>
            generator>
        id>
        <property name="addressdetail"/>
        
        <one-to-one name="person" constrained="true"/>
    class>
hibernate-mapping>

3.有连接表的双向1-1关联
本情形相当罕见，通常不推荐使用这种策略。
xml version="1.0"?>
DOCTYPE hibernate-mapping
    PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "">
<hibernate-mapping package="prolove">
    <class name="Person">
        <id name="personid">
            <generator class="identity"/>
        id>
        <property name="name"/>
        <property name="age"/>
        
        <join table="PersonAddress" optional="true">
            
            <key column="personid" unique="true"/>
            
            <many-to-one name="address" column="addressid"
                not-null="true" unique="true"/>
        join>
    class>
    
    <class name="Address">
        
        <id name="addressid">
            
            <generator class="identity"/>
        id>
        <property name="addressdetail"/>
        
        <join table="PersonAddress" inverse="true" optional="true">
            <key column="addressid" unique="true"/>
            <many-ton-one name="person" column="personid"
                not-null="true" unique="true"/>
        join>
    class>
hibernate-mapping>