Mybatis中的@Select、foreach用法

Mybatis @Select、foreach

foreach属性

Mapper层

List<UserRole> selectIdList(List<Long> userList);

XML语句

<select id="selectIdList" parameterType="java.util.List" resultType="com.yuantu.dev.sys.entity.UserRole">
        SELECT id,user_id,role_id FROM sys_user_role
        WHERE user_id IN
        <foreach collection="list" index="index" item="item" open="(" separator="," close=")">
            #{item}
        </foreach>
</select>

@Select注解

常用查询

@Select("select * from web_admins where id = #{id}")
Admin selectAdminById(@Param("id") Integer id);

在@Select中拼写动态SQL语句

对于条件较复杂的情况，不太建议这种方式，在字符串中难免会有很多错误，可读性很差。

@Select("<script>" +
        "SELECT * FROM users WHERE id in \n" +
        "<foreach collection='usedUserIdList' index='index' item='item' open='(' separator=',' close=')'>#{item}</foreach> \n" +
        "AND open_card_order_state = 1" +
        "</script>")
List<Users> selectUsers(@Param("usedUserIdList") List<Integer> usedUserIdList,Page<Users> page);

Mybatis foreach3种用法

用mybatis实现select 字段 from table where id in(1,2,3,4,5)的sql语句:

mybatis提供的foreach可以实现，foreach有3种传值方式：array，list,map.

其中Array的mapper写法

<select id="selectUserArr" resultMap="BaseResultMap">
    SELECT
    <include refid="Base_Column_List" />
    from user
    where id in
    <foreach collection="array" item="id" open="(" separator="," close=")">
        #{id}
    </foreach>
</select>

注：array的写法中collection中的值必须是array,不能写Array，会报错的。但传参的命名可以不是array

List<User>selectUserArr(int []arr);
List<User>userArray=userMapper.selectUserArr(arr);

list的写法

<select id="selectUserList" resultMap="BaseResultMap">
    SELECT
    <include refid="Base_Column_List" />
    from user
    where id in
    <foreach collection="list" item="id" open="(" separator="," close=")">
        #{id}
    </foreach>
</select>

注：list写法中collection中的值必须是list,也不能是List,但传来的参数命名可以不一定是list

List<User>selectUserList(List list1);
List<User>userList=userMapper.selectUserList(list1);

map的写法

<select id="selectUserMap" resultMap="BaseResultMap">
    SELECT
    <include refid="Base_Column_List" />
    from user
    where id in
    <foreach collection="map1" item="id" open="(" separator="," close=")">
        #{id}
    </foreach>
</select>

注：map写法中的collection中填的是map的key值，不对应就会报错

List<User>selectUserMap(Map map);
map.put("map1",map1);
List<User> userMap=userMapper.selectUserMap(map);

在springboot的启动类测试：

@SpringBootApplication
@MapperScan("springboot.mapper")
public class Application
{
    public static void main( String[] args )
    {
        ApplicationContext context  = SpringApplication.run(Application.class, args);
       
        UserMapper userMapper=context.getBean(UserMapper.class);

        int []arr=new int[5];
        List list1=new ArrayList();
        Map<String,Object> map=new HashMap<String, Object>(5);
        int i;
        for(i=1;i<5;i++){
            arr[i-1]=i;
            list1.add(i);

        }
        int []map1={1,2,3,4,5};
        map.put("map1",map1);
        List<User>userArray=userMapper.selectUserArr(arr);
        List<User>userList=userMapper.selectUserList(list1);
        List<User> userMap=userMapper.selectUserMap(map);

        System.out.println("Array=============");
        sys(userArray);
        System.out.println("list=============");
        sys(userList);
        System.out.println("map:================");
        sys(userMap);

    public static void sys(List<User> list){
        for (User user : list){
            System.out.println("user:"+user.toString());
        }
    }
}

效果如下：

    Array=============
        user:User{id=1, uname='小黑', upwd='123', unum='123', sex=0, age=18, addr='广东', tid=1}
        user:User{id=2, uname='小白', upwd='234', unum='234', sex=1, age=21, addr='广州', tid=1}
        user:User{id=3, uname='小红', upwd='345', unum='345', sex=0, age=15, addr='天河区', tid=2}
        user:User{id=4, uname='小小', upwd='123', unum='567', sex=1, age=21, addr='null', tid=3}
        list=============
        user:User{id=1, uname='小黑', upwd='123', unum='123', sex=0, age=18, addr='广东', tid=1}
        user:User{id=2, uname='小白', upwd='234', unum='234', sex=1, age=21, addr='广州', tid=1}
        user:User{id=3, uname='小红', upwd='345', unum='345', sex=0, age=15, addr='天河区', tid=2}
        user:User{id=4, uname='小小', upwd='123', unum='567', sex=1, age=21, addr='null', tid=3}
        map:================
        user:User{id=1, uname='小黑', upwd='123', unum='123', sex=0, age=18, addr='广东', tid=1}
        user:User{id=2, uname='小白', upwd='234', unum='234', sex=1, age=21, addr='广州', tid=1}
        user:User{id=3, uname='小红', upwd='345', unum='345', sex=0, age=15, addr='天河区', tid=2}
        user:User{id=4, uname='小小', upwd='123', unum='567', sex=1, age=21, addr='null', tid=3}
        user:User{id=5, uname='柘城', upwd='123', unum='423', sex=0, age=23, addr='null', tid=2}

来源：https://blog.csdn.net/weixin_42286635/article/details/103564226