SpringBoot+MyBatis进行XML中循环处理List参数的终极指南

SELECT * FROM users WHERE id IN (1, 2, 3, 4)

// ！！！必须导入MyBatis的@Param包！！！
import org.apache.ibatis.annotations.Param;

public interface UserMapper {
    // 使用@Param注解指定参数名
    List<User> selectByIds(@Param("idList") List<Long> idList);
}

<select id="selectByIds" resultType="User">
    SELECT * FROM users
    WHERE id IN
    <foreach collection="idList" item="id" 
             open="(" separator="," close=")">
        #{id}
    </foreach>
</select>

SELECT * FROM users WHERE id IN (1, 2, 3)

// ❌ 错误：导入了Spring的Param包
import org.springframework.data.repository.query.Param;

// ✅ 正确：必须使用MyBatis的Param包
import org.apache.ibatis.annotations.Param;

// ❌ 错误：缺少@Param注解会导致XML中无法识别参数
List<User> selectByIds(List<Long> idList);

// ✅ 正确：必须添加@Param注解
List<User> selectByIds(@Param("idList") List<Long> idList);

public List<User> getUsersByIds(List<Long> ids) {
    return userMapper.selectList(
        new QueryWrapper<User>().in("id", ids)
    );
}

public List<User> getUsersByIds(List<Long> ids) {
    return userMapper.selectList(
        Wrappers.<User>lambdaQuery()
            .in(User::getId, ids)
    );
}

// Mapper
List<User> selectByNames(@Param("nameList") List<String> nameList);

// XML
<foreach collection="nameList" item="name" open="(" separator="," close=")">
    #{name}
</foreach>

// Mapper
List<User> selectByConditions(@Param("userList") List<User> userList);

// XML
<foreach collection="userList" item="user" separator=" OR ">
    (name = #{user.name} AND age > #{user.age})
</foreach>

// Mapper
List<User> searchUsers(@Param("ids") List<Long> ids, 
                      @Param("names") List<String> names);

// XML
<where>
    <if test="ids != null and !ids.isEmpty()">
        id IN
        <foreach collection="ids" item="id" open="(" separator="," close=")">
            #{id}
        </foreach>
    </if>
    <if test="names != null and !names.isEmpty()">
        AND name IN
        <foreach collection="names" item="name" open="(" separator="," close=")">
            #{name}
        </foreach>
    </if>
</where>

// Mapper
List<User> selectByStatus(@Param("statusList") List<UserStatus> statusList);

// XML
<foreach collection="statusList" item="status" open="(" separator="," close=")">
    #{status, typeHandler=org.apache.ibatis.type.EnumTypeHandler}
</foreach>

// Mapper
List<User> selectByDates(@Param("dateList") List<Date> dates);

// XML
<foreach collection="dateList" item="date" separator=" OR ">
    create_time BETWEEN #{date} AND DATE_ADD(#{date}, INTERVAL 1 DAY)
</foreach>

<select id="safeSelect">
    SELECT * FROM users
    <where>
        <if test="idList != null and !idList.isEmpty()">
            id IN
            <foreach collection="idList" ... />
        </if>
    </where>
</select>

// 每500条执行一次查询
public List<User> batchSelect(List<Long> allIds) {
    List<User> result = new ArrayList<>();
    int batchSize = 500;
    
    for (int i = 0; i < allIds.size(); i += batchSize) {
        List<Long> batchIds = allIds.subList(i, Math.min(i + batchSize, allIds.size()));
        result.addAll(userMapper.selectByIds(batchIds));
    }
    return result;
}

<!-- 安全写法：使用#{}预编译 -->
<foreach collection="names" item="name">
    #{name}  <!-- 安全 -->
</foreach>

<!-- 危险写法：${}直接拼接 -->
<foreach collection="names" item="name">
    '${name}' <!-- 存在SQL注入风险！ -->
</foreach>

@RestController
@RequestMapping("/users")
public class UserController {
    
    @PostMapping("/by-ids")
    public List<User> getUsersByIds(@RequestBody List<Long> ids) {
        return userService.getUsersByIds(ids);
    }
}

@Service
@RequiredArgsConstructor
public class UserService {
    private final UserMapper userMapper;

    public List<User> getUsersByIds(List<Long> ids) {
        if (ids == null || ids.isEmpty()) {
            return Collections.emptyList();
        }
        // 超过1000条自动分批
        return ids.size() > 1000 ? batchSelect(ids) : userMapper.selectByIds(ids);
    }
}

<mapper namespace="com.example.mapper.UserMapper">
    
    <select id="selectByIds" resultType="User">
        SELECT id, name, email 
        FROM users
        <where>
            <if test="idList != null and !idList.isEmpty()">
                id IN
                <foreach collection="idList" item="id" 
                         open="(" separator="," close=")">
                    #{id}
                </foreach>
            </if>
        </where>
    </select>
</mapper>

<foreach collection="参数名" item="元素名" 
         open="开始符" separator="分隔符" close="结束符">
     #{元素名}
</foreach>