mybatis中的mapper.xml如何使用foreach标签呢?

下文笔者讲述mybatis中如何在xml中配置foreach标签的方法及示例分享,如下所示

foreach简介

foreach标签用于处理 集合 数组 map的参数

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foreach中常见的属性:
    <foreach collection="list" index="index" item="user" open="(" close=")" separator=",">
       #{user}
    </foreach>

    item：  集合中元素迭代时的别名，该参数为必选，通过别名进行取值
    index：在list和数组中,index是元素的序号，在map中，index是元素的key，非必填
    open： foreach代码的开始符号，一般是(和close=")"合用。常用在in(),values()时
	   非必填
    separator：元素之间的分隔符，例如在in()的时候，separator=","
	   会自动在元素中间用“,“隔开 
	    避免手动输入逗号导致sql错误，如in(1,2,)这样。非必填
    close: foreach代码的关闭符号，一般是)和open="("合用。常用在in(),values()时。非必填
    collection: 要做foreach的对象，作为入参
        传入是集合，也就是接口里面用的  List<String> nameList    那么 使用 collection = “list”
        传入的是数组，接口里面 String[] namestrs ,那么 使用 collection = “array”
        如果传入的是一个实体bean，实体bean里面有一个属性为 list<String> ids 那么collection = “ids ”
		   当实体bean中对应ids是一个对象，ids 里面有一个属性为 List<Stirng> usernames
		    则collection = “ids.usernames”

foreach的使用示例

int queryUserCount(List<String> ids); mapper映射xml： <select id="queryDiscDerateCount" resultType="Integer"> select count(*) from t_mchnt_disc_config where mchnt_cd in <foreach collection="list" index="index" item="id" open="(" close=")" separator=","> #{id} </foreach> </select> 实体类 list<User> userlist,实体类中有 list 属性 实体类： @Data public class UserDto { private String userId = ""; } mapper接口 List<UserDto> getDiscDerateList(List<UserDto> discDto); mapper映射xml： <select id="getDiscDerateList" parameterType="UserDto" resultType="UserDto"> select * users where id in <foreach collection="list" index="index" item="user" open="(" close=")" separator=","> #{user.userId} </foreach> </select> 数组String[] params 用array mapper 接口 int queryUserCount(String[] ids); mapper映射xml： <select id="queryUserCount" resultType="Integer"> select count(*) from users where userId in <foreach collection="array" index="index" item="id" open="(" close=")" separator=","> #{id} </foreach> </select> 传入参数为实体类 且实体中包含数组和集合 实体类 @Data public class UserVo { private Long id; private Long supplierId; private Long[] ids; private List<Long> clientIdList; } mapper接口 List<UserVo> queryList(UserVo select); mapper映射文件xml <select id="queryList" resultType="UserVo" parameterType="UserVo"> select * from bz_info <where> and id in <foreach collection="ids" open="(" close=")" item="id" separator=","> #{id} </foreach> and client_id in <foreach collection="clientIdList" separator="," item="detail" open="(" close=")" > #{detail} </foreach> </where> </select> 传入多个list或者array 无需实体进行封装 使用注解@Params, collection使用到Param中定义的别名 mapper接口 List<UserVo> queryList(@Param("idArray") Long[] array, @Param("clientIdList") List<Long> list); mapper映射文件xml <select id="queryList" resultType="UserVo"> select * from t_user_info <where> and id in <foreach collection="idArray" open="(" close=")" item="id" separator=","> #{id} </foreach> and client_id in <foreach collection="clientIdList" separator="," item="detail" open="(" close=")" > #{detail} </foreach> </where> </select> map参数 当传入参数为 Map<String,Objject> 也可使用foreach List<SysUser> getUserByIds(Map<String,Object> map); // xml <select id="getUserByIds" resultMap="BaseResultMap"> select * from t_user_info where status = #{status} and id in <foreach collection="ids" item="id" open="(" close=")" separator=","> #{id} </foreach> </select> 代码测试 @Test public void testMapUsers() { Map<String,Object> params = new HashMap<>(); params.put("status", "1"); params.put("ids", Arrays.asList(1,2,3,4,5,6,7,8)); List<SysUser> all = sysUserDao.getUserByIds(params); try { System.out.println(new JsonMapper().writeValueAsString(all)); } catch (JsonProcessingException e) { e.printStackTrace(); } }