Hibernate的对象关系映射（6）

2.4 集合映射

java的collection和数组都可以被映射，意义在于表示数据之间的关联，对于hibernate管理的数据而言，java的集合对象主要起到了接口的作用。

2.4.1 Map

(1) index和element

<?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="com.weportal.collection">
    <class name="Team">
        <id name="id">
            <generator class="hilo"/>
        </id>
        <property name="name" column="NAME" />
        <map name="members"  order-by="name,teamRole" >
            <key foreign-key="fk">
                <column name="teamNumber"/>
            </key>
            <index column="teamRole" type="string"/>
            <element column="name" type="string"/>
        </map>    
    </class>
</hibernate-mapping>

 (2) one-to-many

例如：如果将属性members（集合类型）映射到持久化类，需要使用one-to-many或者many-to-many。映射文件如下：

<?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="com.weportal.collection">
    <class name="Team">
        <id name="id">
            <generator class="hilo"/>
        </id>
        <property name="name" column="NAME" />
        <map name="members"  inverse="false" >
            <key column="team" foreign-key="fk">
            </key>
            <index column="teamRole" type="string"/>
            <one-to-many class="Member"/>
        </map>    
    </class>
    <class name="Member">
        <id name="id">
            <generator class="native"></generator>
        </id>
        <property name="name"></property>
        <property name="age"></property>
        <many-to-one name="team"></many-to-one>
    </class>
</hibernate-mapping>

(3) many-to-many

建立这种多对多的关系不是一个优秀的方案。

(4) composite-index

Map中的index元素可以被替换为存储组件对象的composite-index，利用composite-index可将组件用于index。

<?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="com.weportal.collection">
    <class name="Team">
        <id name="id">
            <generator class="native"/>
        </id>
        <property name="name" column="NAME" />
        <map name="members" inverse="false">
            <key column="team" foreign-key="fk"/>
            <composite-index class="Position">
                <key-property name="role"/>
                <key-property name="scene"/>
                <key-many-to-one name="bestChoice" class="Member"/>
            </composite-index>
            <one-to-many class="Member"/>
        </map>
    </class>
    <class name="Member">
        <id name="id">
            <generator class="native"/>
        </id>
        <property name="name"/>
        <property name="age"/>
        <many-to-one name="team"/>
    </class>
</hibernate-mapping>

(5) index-many-to-many

index不仅可以是组件，也可以是持久化类的实体。

<?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="com.weportal.collection">
    <class name="Team">
        <id name="id">
            <generator class="native"/>
        </id>
        <property name="name" column="NAME" />
        <map name="members" inverse="false">
            <key column="team" foreign-key="fk"/>
            <index-many-to-many class="Position" column="id"></index-many-to-many>
            <one-to-many class="Member"/>
        </map>
    </class>
    <class name="Member">
        <id name="id">
            <generator class="native"/>
        </id>
        <property name="name"/>
        <property name="age"/>
        <many-to-one name="team"/>
    </class>
    <class name="Position">
        <id name="id">
            <generator class="native"/>
        </id>
        <property name="role"/>
        <property name="scene"/>
        <many-to-one name="bestChoice"/>
    </class>    
</hibernate-mapping>

(6) index-many-to-any

index还可以插入any类型的数据，any在hibernate中代表不确定的类型。

<?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="com.weportal.collection">
    <class name="Team">
        <id name="id">
            <generator class="native"/>
        </id>
        <property name="name" column="NAME" />
        <map name="members" inverse="false">
            <key column="team" foreign-key="fk"/>
            <index-many-to-any id-type="long" meta-type="string">
             <column name="index_class"></column>
             <column name="index_id"></column>             
            </index-many-to-any>
            <one-to-many class="Position"/>
        </map>
    </class>
    <class name="Member">
        <id name="id">
            <generator class="native"/>
        </id>
        <property name="name"/>
        <property name="age"/>
        <many-to-one name="team"/>
    </class>    
    <class name="Position">
        <id name="id">
            <generator class="native"/>
        </id>
        <property name="role"/>
        <property name="scene"/>
        <many-to-one name="bestChoice"/>
    </class>        
</hibernate-mapping>

(7) many-to-any

value的值也可设为any类型。

<?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="com.weportal.collection">
    <class name="Team">
        <id name="id">
            <generator class="native"/>
        </id>
        <property name="name" column="NAME" />
        <map name="members" inverse="false">
            <key column="team" foreign-key="fk"/>
            <index-many-to-any id-type="long" meta-type="string">
             <column name="index_class"></column>
             <column name="index_id"></column>             
            </index-many-to-any>
            <many-to-any id-type="long" meta-type="string">
             <column name="value_class"></column>
             <column name="value_id"></column>
            </many-to-any>
        </map>
    </class>
    <class name="Member">
        <id name="id">
            <generator class="native"/>
        </id>
        <property name="name"/>
        <property name="age"/>
        <many-to-one name="team"/>
    </class>    
    <class name="Position">
        <id name="id">
            <generator class="native"/>
        </id>
        <property name="role"/>
        <property name="scene"/>
        <many-to-one name="bestChoice"/>
    </class>        
</hibernate-mapping>

(8) composite-element

可以用来声明更复杂的数据元素。

<?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="com.weportal.collection">
    <import class="Member"></import>
    <class name="Team">
        <id name="id">
            <generator class="native"/>
        </id>
        <property name="name" column="NAME" />
        <map name="members" table="teamMembers">
            <key column="teamId"/>
            <index column="teamRole" type="string"/>
            <composite-element class="Member">
                <parent name="team"/>
                <property name="name"/>
                <property name="age"/>                
            </composite-element>
        </map>
    </class>
</hibernate-mapping>

可以利用nested-composite-element在类中嵌套类。

<?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="com.weportal.collection">
    <import class="Member"></import>
    <class name="Team">
        <id name="id">
            <generator class="native"/>
        </id>
        <property name="name" column="NAME" />
        <map name="members" table="teamMembers">
            <key column="teamId"/>
            <index column="teamRole" type="string"/>
            <composite-element class="Member">
                <parent name="team"/>
                <property name="name"/>
                <property name="age"/>
                <nested-composite-element name="assistantMember" class="Member">
                    <property name="name" column="assistant"></property>
                </nested-composite-element>            
            </composite-element>
        </map>
    </class>
</hibernate-mapping>

(9) Map的排序

利用sort和order-by属性来声明。

(10) Map的子元素和属性

略