【转】mybatis中foreach使用方法

http://www.cnblogs.com/zzgno1/p/4184601.html

foreach一共有三种类型，分别为List,[](array),Map三种。

foreach属性

示例一：

<select id="countByUserList" resultType="_int" parameterType="list">
select count(*) from users
  <where>
    id in
    <foreach item="item" collection="list" separator="," open="(" close=")" index="">
      #{item.id, jdbcType=NUMERIC}
    </foreach>
  </where>
</select>

注：select count(*) from users WHERE id in ( ? , ? )

示例二：

    <select id="selectStorageProductInventroy" parameterType="java.util.Map" resultType="StorageProductInventroyModel">
        select op.inventroy_operation_id  ,
        op.inventroy_id  ,
        ty.name as operation_type,
        DATE_FORMAT(op.insert_time,‘%Y/%m/%d‘) as insert_time,
        em.name as employee,
        sm1.name as from_store,
        st1.name as to_store,
        sm.name as from_storage,
        st.name as to_storage,
        hi.number,
        pr.name as product_name,
        pr.category_id as categoryString,
        pr.product_code,
        hi.amount,
        hi.back_amount,
        hi.unit,
        re.description as operation_reason,
        hi.description

        from inventroy_history hi  left join inventroy_operation  op
        on hi.inventroy_operation_id = op.inventroy_operation_id

        left join product pr
        on hi.product_id =pr.product_id

        left join operation_type ty
        on op.operation_type_id = ty.operation_type_id

        left join employee em
        on op.employee_id = em.employee_id

        left join   (select  inventroy_operation.to_storage_id as to_storage_id,storage.name as name
        from  inventroy_operation , storage
        where inventroy_operation.to_storage_id = storage.storage_id) st
        on op.to_storage_id = st.to_storage_id

        left join   (select  inventroy_operation.from_storage_id as from_storage_id,storage.name as name
        from  inventroy_operation , storage
        where inventroy_operation.from_storage_id = storage.storage_id) sm
        on op.from_storage_id = sm.from_storage_id

        left join   (select  inventroy_operation.to_store_id as to_store_id,store.name as name
        from  inventroy_operation , store
        where inventroy_operation.to_store_id = store.store_id) st1
        on op.to_store_id = st1.to_store_id

        left join   (select  inventroy_operation.from_store_id as from_store_id,store.name as name
        from  inventroy_operation , store
        where inventroy_operation.from_store_id = store.store_id) sm1
        on op.from_store_id = sm1.from_store_id

        left join operation_reason re
        on hi.operation_reason_id = re.operation_reason_id
        WHERE 1=1
        <if test="operation_type_id != null and operation_type_id.length != 0">
            and
            <foreach collection="operation_type_id" item="operationTypeId" index="index"  open="(" separator="or" close=")">
                op.operation_type_id = #{operationTypeId}
            </foreach>
        </if>
        <if test="storage_id != 0 and storage_id != null">
            and (op.from_storage_id = #{storage_id} or op.to_storage_id = #{storage_id})
        </if>
        <if test="category_id != 0 and category_id != null">
            and pr.category_id like concat(‘%‘,‘(‘,#{category_id},‘)‘,‘%‘)
        </if>
        <if test="product_code != null">
            and pr.product_code like concat(‘%‘,#{product_code},‘%‘)
        </if>
        <if test="product_name != null">
            and pr.name  like concat(‘%‘,#{product_name},‘%‘)
        </if>
        and date(op.insert_time) between #{start_time} and #{end_time}
        group by hi.inventroy_history_id
    </select>

注：and （op.operation_type_id = ？ or op.operation_type_id = ？）

示例三：数组

 public void testQuery() {
        ColInfoDao dao=(ColInfoDao)ctx.getBean("colInfoDao");
        Map map = new HashMap();
        map.put("userId", "tom");
        map.put("password", "123");
        String[] a = { "20000001", "20000002" };
        map.put("classIds", Arrays.asList(a));
        Object password = dao.query(map);
        System.out.println("password:" + password);
        Assert.assertEquals("123", password);
    }

XML：（感觉不适合mybatis，可以使用在ibatis中，iBatis 2.x 和 MyBatis 3.0.x）

<select id="queryPasswordByUserId" parameterClass="java.util.Map"      resultClass="java.lang.String">
        <![CDATA[
        select PASSWORD as password from T_S_P_USER
        ]]>
        <dynamic prepend="where">
            <isNotEmpty prepend="AND" property="userId">
                USER_ID=#userId#
            </isNotEmpty>
            <isNotEmpty prepend="AND" property="password">
                PASSWORD=#password#
            </isNotEmpty>
            <isNotEmpty prepend="AND" property="classIds">
                <iterate property="classIds" open="(" conjunction="OR" close=")">
                    CLASS_ID = #classIds[]#
                </iterate>
            </isNotEmpty>
        </dynamic>
</select>

示例四：Map

map和List,array相比，map是用K,V存储的，在foreach中，使用map时，index属性值为map中的Key的值。

因为map中的Key不同于list,array中的索引，所以会有更丰富的用法。

<insert id="ins_string_string">
        insert into string_string (key, value) values
        <foreach item="item" index="key" collection="map"
            open="" separator="," close="">(#{key}, #{item})</foreach>
</insert>

可以看到这个例子相当简单，表中需要两个值，正好和K,V对应，因而map中的一个K,V就对应一条数据，如果map中有多个K,V，就会保存多个结果。

如果map中有两对K,V，那么执行SQL如下：

DEBUG [main] - ==>  Preparing: insert into string_string (key, value) values (?, ?) , (?, ?)
DEBUG [main] - ==> Parameters: key 1(String), value 1(String), key 2(String), value 2(String)
DEBUG [main] - <==    Updates: 2

下面再看一个select的例子：

<select id="sel_key_cols" resultType="int">
        select count(*) from key_cols where
        <foreach item="item" index="key" collection="map"
            open="" separator="AND" close="">${key} = #{item}</foreach>
</select>

可以看到这里用key=value来作为查询条件，对于动态的查询，这种处理方式可以借鉴。一定要注意到$和#的区别，$的参数直接输出，#的参数会被替换为?，然后传入参数值执行。

DEBUG [main] - ==>  Preparing: select count(*) from key_cols where col_a = ? AND col_b = ?
DEBUG [main] - ==> Parameters: 22(Integer), 222(Integer)
DEBUG [main] - <==      Total: 1

最后，如果不考虑元素的顺序和map中Key，map和list,array可以拥有一样的效果，都是存储了多个值，然后循环读取出来。