Mybatis中的foreach的主要用在构建in条件中，它可以在SQL语句中进行迭代一个集合。
foreach元素的属性主要有 item，index，collection，open，separator，close：
item：表示集合中每一个元素进行迭代时的别；
index：指定一个名字，用于表示在迭代过程中，每次迭代到的位置；
open：表示该语句以什么开始；
separator：表示在每次进行迭代之间以什么符号作为分隔 符；
close：表示以什么结束；
collection：
在使用foreach的时候最关键的也是最容易出错的就是collection属性，该属性是必须指定的，但是在不同情况 下，该属性的值是不一样的，主要有一下3种情况：
1. 如果传入的是单参数且参数类型是一个List的时候，collection属性值为list
2. 如果传入的是单参数且参数类型是一个array数组的时候，collection的属性值为array
3. 如果传入的参数是多个的时候，我们就需要把它们封装成一个Map了，当然单参数也可以封装成map，实际上如果你在传入参数的时候，在breast里面也是会把它封装成一个Map的，map的key就是参数名，所以这个时候collection属性值就是传入的List或array对象在自己封装的map里面的key
下面分别来看看上述三种情况的示例代码：
<1>单参数List的类型：
<select id="dynamicForeachTest" resultType="Blog">
select * from t_blog where id in
<foreach collection="list" index="index" item="item" open="(" separator="," close=")">
#{item}
</foreach>
</select>
上述collection的值为list，对应的Mapper是这样的：
public List<Blog> dynamicForeachTest(List<Integer> ids);
测试代码：
@Test
public void dynamicForeachTest() {
SqlSession session = Util.getSqlSessionFactory().openSession();
BlogMapper blogMapper = session.getMapper(BlogMapper.class);
List<Integer> ids = new ArrayList<Integer>();
ids.add(1);
ids.add(3);
ids.add(6);
List<Blog> blogs = blogMapper.dynamicForeachTest(ids);
for (Blog blog : blogs){
System.out.println(blog);
}
session.close();
}
<2>单参数Array的类型：
<select id="dynamicForeach2Test" resultType="Blog">
select * from t_blog where id in
<foreach collection="array" index="index" item="item" open="(" separator="," close=")">
#{item}
</foreach>
</select>
上述collection为array，对应的Mapper代码：
public List<Blog> dynamicForeach2Test(int[] ids);
对应的测试代码：
@Test
public void dynamicForeach2Test() {
SqlSession session = Util.getSqlSessionFactory().openSession();
BlogMapper blogMapper = session.getMapper(BlogMapper.class);
int[] ids = new int[] {1,3,6,9};
List<Blog> blogs = blogMapper.dynamicForeach2Test(ids);
for (Blog blog : blogs){
System.out.println(blog);
}
session.close();
}
<3>多参数封装成Map的类型：
<select id="dynamicForeach3Test" resultType="Blog">
select * from t_blog where title like "%"#{title}"%" and id in
<foreach collection="ids" index="index" item="item" open="(" separator="," close=")">
#{item}
</foreach>
</select>
上述collection的值为ids，是传入的参数Map的key，对应的Mapper代码：
public List<Blog> dynamicForeach3Test(Map<String, Object> params);
对应测试代码：
@Test
public void dynamicForeach3Test() {
SqlSession session = Util.getSqlSessionFactory().openSession();
BlogMapper blogMapper = session.getMapper(BlogMapper.class);
final List<Integer> ids = new ArrayList<Integer>();
ids.add(1);
ids.add(2);
ids.add(3);
ids.add(6);
Map<String, Object> params = new HashMap<String, Object>();
params.put("ids", ids);
params.put("title", "中国");
List<Blog> blogs = blogMapper.dynamicForeach3Test(params);
for (Blog blog : blogs)
System.out.println(blog);
session.close();
}
<4>嵌套foreach的使用：
map 数据如下 Map<String,List<Long>>
测试代码如下：
public void getByMap(){
Map<String,List<Long>> params=new HashMap<String, List<Long>>();
List<Long> orgList=new ArrayList<Long>();
orgList.add(10000003840076L);
orgList.add(10000003840080L);
List<Long> roleList=new ArrayList<Long>();
roleList.add(10000000050086L);
roleList.add(10000012180016L);
params.put("org", orgList);
params.put("role", roleList);
List<BpmDefUser> list= bpmDefUserDao.getByMap(params);
System.out.println(list.size());
}
dao代码如下：
public List<BpmDefUser> getByMap(Map<String,List<Long>> map){
Map<String,Object> params=new HashMap<String, Object>();
params.put("relationMap", map);
return this.getBySqlKey("getByMap", params);
}
xml代码如下：
<select id="getByMap" resultMap="BpmDefUser">
<foreach collection="relationMap" index="key" item="ent" separator="union">
SELECT *
FROM BPM_DEF_USER
where RIGHT_TYPE=#{key}
and OWNER_ID in
<foreach collection="ent" item="id" separator="," open="(" close=")">
#{id}
</foreach>
</foreach>
</select>
index 作为map 的key。item为map的值，这里使用了嵌套循环，嵌套循环使用ent。
《项目实践》
@Override
public Container<Map<String,Object>> findAuditListInPage(
Map<String, Object> params) {
//1、参数组装
PageModel pageMode = new PageModel();
try {
if(params.get("page")!=null){
pageMode.setPage(Integer.parseInt(params.get("page").toString()));
}
if(params.get("rows")!=null){
pageMode.setRows(Integer.parseInt(params.get("rows").toString()));
}
} catch (Exception e) {
Assert.customException(RestApiError.COMMON_ARGUMENT_NOTVALID);
}
//分页条件组装
pageMode.putParam(params);
if(params.get("startCreateTime") !=null){
Date parse = DateUtil.parse(params.get("startCreateTime").toString(), DateUtil.yyyyMMddHHmmss);
params.put("startCreateTime",parse);
}
if(params.get("endCreateTime") !=null){
Date parse = DateUtil.parse(params.get("endCreateTime").toString(), DateUtil.yyyyMMddHHmmss);
params.put("endCreateTime",parse);
}
if(params.get("type") !=null){ //type可以多选
String typeString = params.get("type").toString();
String typeArray [] = typeString.split(",");
params.put("type", typeArray);
}
if(params.get("state") !=null){ //state可以多选
String stateString = params.get("state").toString();
if(stateString.equals(DictConstants.APPLICATION_STATE.AUDITING)
||stateString.equals(DictConstants.APPLICATION_STATE.WAITING_AUDIT)){
stateString = "waitingAudit,auditing";
}
String stateArray [] = stateString.split(",");
params.put("state", stateArray);
}
//分页数据组装
Container<Map<String,Object>> container = new Container<Map<String,Object>>();
List<Map<String,Object>> auditModelList = cmApplicationRepo.findAuditList(params);
for(Map<String,Object> audit:auditModelList){
//设置是否关注过
Long auditId = Long.parseLong(audit.get("auditId").toString());
Long auditPersonId = Long.parseLong(params.get("auditPersonId").toString());
Map<String, Object> followMap = new HashMap<String,Object>();
followMap.put("sourceType", DictConstants.FOLLOW_SOURCE_TYPE.FOLLOW_APPLICATION);
followMap.put("sourceId", auditId);
followMap.put("userId", auditPersonId);
List<BizFollowModel> followList = bizFollowService.find(followMap);
if(followList!= null && followList.size()>0){
audit.put("isFollow", "true");
}else{
audit.put("isFollow", "false");
}
}
container.setList(auditModelList);
container.setTotalNum(cmApplicationRepo.countAuditListNumber(params));
return container;
}
DAO
@Override
public List<Map<String,Object>> findAuditList(Map<String, Object> map) {
return findList("getAuditList", map);
}
xml
<!-- 查询申请列表-->
<select id="getApplicationList" resultType="java.util.Map" parameterType="map">
select
a.ID AS id,
a.STATE AS stateCode, b.DICT_VALUE AS stateValue,
a.ITEM AS itemCode, c.DICT_VALUE AS itemValue,
a.TYPE AS typeCode, d.DICT_VALUE AS typeValue,
a.APP_PERSON_ID AS appPersonId,
a.CREATE_TIME AS createTime
from cm_application a
LEFT JOIN cm_dict_type b on a.STATE = b.DICT_CODE AND b.TYPE = 'Application_State'
LEFT JOIN cm_dict_type c on a.ITEM = c.DICT_CODE
LEFT JOIN cm_dict_type d on a.TYPE = d.DICT_CODE
where 1=1
<if test="item != null" >
and a.ITEM = #{item,jdbcType=VARCHAR}
</if>
<if test="type != null" >
and a.TYPE IN
<foreach item="typeArray" index="index" collection="type" open="(" separator="," close=")">
#{typeArray}
</foreach>
</if>
<if test="appPersonId != null" >
and a.APP_PERSON_ID = #{appPersonId,jdbcType=BIGINT}
</if>
<if test="state != null" >
and a.STATE IN
<foreach item="stateArray" index="index" collection="state" open="(" separator="," close=")">
#{stateArray}
</foreach>
</if>
<!-- 分页查询时，要选择createTime在starCreateTime和endCreatetTime之间的记录 -->
<if test="startCreateTime != null" >
and a.CREATE_TIME >= #{startCreateTime,jdbcType=TIMESTAMP}
</if>
<if test="endCreateTime != null" >
and a.CREATE_TIME <= #{endCreateTime,jdbcType=TIMESTAMP}
</if>
order by a.ID
<include refid="Paging" />
</select>