Hibernate的单向关联和双向关联-优快云博客

本文链接：https://blog.youkuaiyun.com/magicboylinw/article/details/8512253

本文介绍了Hibernate中的单向关联和双向关联概念。在单向关联中，关联关系由父类维护，子类无法访问。而在双向关联中，通过inverse属性可以指定管理方，允许双方互相引用。配置上，单向关联使用<one-to-many>，双向关联则需要<many-to-one>配合使用。

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当使用单向关联时，由父类管理关联关系，子类无法管理；而这时，父亲知道自己的儿子，但是，儿子对象不知道父亲是谁。

单向关联时，只需指定<one-to-many> 。

当使用双向关联时，关联关系的管理可以通过inverse指定，这时，儿子能清楚的知道自己的父亲是谁。

双向关联时，还需要指定<many-to-one>。

例如：

public class DbView {
	@Expose
	private Long viewId;
	@Expose
	private String name;
	@Expose
	private Timestamp createTime;
	
	private Set wsIntefaces = new HashSet(0);      //反向关联，子类也知道父类是谁
	private Set dbViewColums = new HashSet(0);
}

public class DbViewColum {
	@Expose
	private Long id;
	@Expose
	private DbView dbView;     //正向关联，父类管理子类
	@Expose
	private String columnName;
	@Expose
	private char  columnType;
}

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- 
    Mapping file autogenerated by MyEclipse Persistence Tools
-->
<hibernate-mapping>
    <class name="com.gdsc.model.ws.DbView" table="db_view">
        <id name="viewId" type="java.lang.Long">
            <column name="view_id" />
            <generator class="native" />
        </id>
        <property name="name" type="java.lang.String">
            <column name="view_name" />
        </property>
        <property name="createTime" type="java.sql.Timestamp">
            <column name="createTime" length="23" />
        </property>
        <set name="wsIntefaces" inverse="true">
            <key>
                <column name="view_id" />
            </key>
            <one-to-many class="com.gdsc.model.ws.WsInteface" />
        </set>
        <set name="dbViewColums" inverse="true">
            <key>
                <column name="view_id" />
            </key>
            <one-to-many class="com.gdsc.model.ws.DbViewColum" />
        </set>
    </class>
</hibernate-mapping>

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- 
    Mapping file autogenerated by MyEclipse Persistence Tools
-->
<hibernate-mapping>
    <class name="com.gdsc.model.ws.DbViewColum" table="db_view_colum">
        <id name="id" type="java.lang.Long">
            <column name="id" />
            <generator class="native" />
        </id>
        <many-to-one name="dbView" class="com.gdsc.model.ws.DbView" fetch="select">
            <column name="view_id" />
        </many-to-one>
        <property name="columnName" type="java.lang.String">
            <column name="column_name" />
        </property>
        <property name="columnType" type="java.lang.Character">
            <column name="column_type" />
        </property>
    </class>
</hibernate-mapping>