9 - 动态SQL--foreach

foreach
需要注意一点的是:
collection为set list array时，index为集合的下标, item为元素值
collection为map时，index为key,item为value
dao

List<Student> listStudents(List<Integer> list);

mapper

<select id="listStudents" resultMap="studentMapper">
        select * from `student`
        where `id` in
        <foreach collection="list" item="value" index="indexOrKey" 
                 open="(" separator="," close=")">
            #{value}
        </foreach>
    </select>

test

    @Test
    public void test() {
        SqlSession session = factory.openSession();
        try {
            StudentMapper studentMapper = session.getMapper(StudentMapper.class);
            List<Integer> listIds = new ArrayList<>();
            listIds.add(1000);
            listIds.add(10001);
            List<Student> students = studentMapper.listStudents(listIds);
            if(!students.isEmpty()){
                for (Student student:
                        students) {
                    System.out.println(student);
                }
            }else{
                System.out.println("没有查到结果!");
            }
        } finally {
            session.commit();
            session.close();
        }
    }