Hibernate中多对多关系映射、保存、查询

首先是一些基础模型类的建立：

 

import java.io.Serializable;

public abstract class BaseObject implements Serializable {

    /**  */
    private static final long serialVersionUID = -7443978018690354629L;

    @Override
    public abstract String toString();

    @Override
    public abstract boolean equals(Object o);

    @Override
    public abstract int hashCode();

}

 

public abstract class DefaultIdGeneral extends BaseObject {

    /**  */
    private static final long serialVersionUID = -7483768110342207606L;

    // ID
    protected Long id;

    // 版本号，用于Hibernate乐观锁
    protected Integer version;

    /**
     *
     * hibernate.id column="id" generator-class="native"
     *
     * @return Returns the id.
     */
    public abstract Long getId();

    /**
     * @param id
     *            The id to set.
     */
    public abstract void setId(Long id);

    /**
     *
     * @hibernate.version
     *
     * @return Returns the version.
     */
    public Integer getVersion() {
        return version;
    }

    /**
     * @param version
     *            The version to set.
     */
    public void setVersion(Integer version) {
        this.version = version;
    }
}

 

1、多对多关系映射（房间表与设备进行多对多关系映射），两者之间的关系映射时必需有一端的inverse=true，另一端为false，不能两端的inverse都为true。不然在保存或删除两者间的关系时不会对中间表进行操作。

    1）房间表

import java.util.Set;

import org.apache.commons.lang.builder.EqualsBuilder;
import org.apache.commons.lang.builder.HashCodeBuilder;
import org.apache.commons.lang.builder.ToStringBuilder;

/**
 * title: 建筑中的房间
 *
 * @author Administrator
 * @时间 2009-9-22:下午03:41:43
 * @hibernate.class table="fc_roombasic" dynamic-update="true"
 *                  dynamic-insert="true"
 */
public class MapRoom extends DefaultIdGeneral {

    /**  */
    private static final long serialVersionUID = -3216302518592517083L;

    /** 房间名称 room_name */
    private String name;

    /** 房间内设备 */
    private Set<Equipment> equipments;

    /**
     * @hibernate.id column="room_id" generator-class="native"
     *
     */
    @Override
    public Long getId() {
        return id;
    }

    @Override
    public void setId(Long id) {
        this.id = id;
    }

    /**
     * @hibernate.property column="room_name"
     *
     */
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    /**
     * @hibernate.set table="fc_room_equipment" lazy="true" cascade="all"
     *                inverse="true"
     * @hibernate.collection-many-to-many column="equipment_id"
     *                                    class="com.yinhoo.map.model.Equipment"
     * @hibernate.collection-key column="room_id"
     * @return
     */
    public Set<Equipment> getEquipments() {
        return equipments;
    }

    public void setEquipments(Set<Equipment> equipments) {
        this.equipments = equipments;
    }

    @Override
    public boolean equals(final Object other) {
          ...
    }

    @Override
    public int hashCode() {
          ....
    }

    @Override
    public String toString() {
          .........
    }

}

 2)设备

import java.util.Set;

/**
 * title: 设备信息
 *
 * @author Administrator
 * @时间 2009-9-22:下午09:49:32
 * @hibernate.class table="fc_equip" dynamic-update="true" dynamic-insert="true"
 */
public class Equipment extends DefaultIdGeneral {

    /** 设备名称 */
    private String name;

    /** 使用房间（对应roombasic表room_id） */
    private Set<MapRoom> rooms;

    /**
     * @hibernate.id column="equip_id" generator-class="native"
     *
     */
    @Override
    public Long getId() {
        return id;
    }

    @Override
    public void setId(Long id) {
        this.id = id;
    }

    /**
     * @hibernate.property column="equip_name"
     *
     */
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    /**
     * @hibernate.set table="fc_room_equipment" lazy="true" cascade="all"
     *                inverse="false"
     * @hibernate.collection-many-to-many column="room_id"
     *                                    class="com.yinhoo.map.model.MapRoom"
     * @hibernate.collection-key column="equipment_id"
     * @return
     */
    public Set<MapRoom> getRooms() {
        return rooms;
    }

    public void setRooms(Set<MapRoom> rooms) {
        this.rooms = rooms;
    }

}

2、多对多之间的查询。

public int getMapRoomTotalRecord(Equipment equipment) {
        String sql = "select count(room.id) from MapRoom as room where room.equipments.id="
                + equipment.getId() + " ";
        // System.out.println(sql);
        return ((Long) getSession().createQuery(sql).uniqueResult())
                .intValue();
    }

 

String sql = "select count(room.id) from MapRoom as room join room.equipments as equip where equip.id="
                + equipment.getId() + " ";

 

public int getMapRoomTotalRecord(Equipment equipment) {
        String sql = "select count(room.id) from MapRoom as room join room.equipments as equip where equip= :equipment";
        // System.out.println(sql);
        return ((Long) getSession().createQuery(sql).setParameter("equipment",
                equipment).uniqueResult()).intValue();
    }

 查询结果集：

public List<MapRoom> getMapRooms(Equipment equipment,
            int first, int max) {
        String sql = "select room from MapRoom as room join room.equipments as equip where equip= :equipment ";
        return getSession().createQuery(sql).setParameter("equipment",
                equipment).setFirstResult(first).setMaxResults(max).list();
    }

 

 

下面是参照http://www.blogjava.net/fuhoujun/archive/2009/01/06/232230.html。

一个老师教许多学生,一个学生被许多老师教,一个学生有好多书,同一种书被许多同学拥有.
要查询教拥有书"a"的学生的老师!

Hql语句：

SELECT t FROM Teacher t join t.students s join s.books b where b.name = 'a'

 

 

解释：t.students s中s并不是集合的意思,而是t的students对象的表别名,join t.students s这个hql,hibernate会翻译成两个表的内连接关系

错误写法：

SELECT t FROM teacher t where t.students.books.name = 'a'

 

 

其实道理是很显然的,t.students是一个Set,那么这个Set怎么可能有books这样的属性呢?同理books.name也不对,所以使用表间连接并给出别名t.students s,此时的对象s才有books属性,所以可以写s.booksb,最后使用b.name限制查询b.name = 'a'. 

另外一种写法：

SELECT t FROM Teacher t,Student s,Book b where s.id in elements(t.students) and b.id in elements(s.books)

 

这种方法没有出错!不过这种方式要用子查询!

原文地址：http://conkeyn.iteye.com/blog/487271