Mybatis学习笔记14 - 动态sql之foreach标签

示例代码：

接口定义：
package com.mybatis.dao;

import com.mybatis.bean.Employee;
import org.apache.ibatis.annotations.Param;

import java.util.List;

public interface EmployeeMapper {
    //查询员工id在给定集合中的
    public List<Employee> getEmpsByConditionForeach(@Param("ids") List<Integer> ids);
}


mapper定义：
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.mybatis.dao.EmployeeMapper">
    <!--
        collection：指定要遍历的集合：
            list类型的参数会特殊处理封装在map中，map的key就叫list
        item：将当前遍历出的元素赋值给指定的变量
        separator:每个元素之间的分隔符
        open：遍历出所有结果拼接一个开始的字符
        close:遍历出所有结果拼接一个结束的字符
        index:索引。遍历list的时候index就是索引，item就是当前值
                      遍历map的时候index表示的就是map的key，item就是map的值
        #{变量名} 取出变量的值也就是当前遍历出的元素
      -->
    <select id="getEmpsByConditionForeach" resultType="com.mybatis.bean.Employee">
        select * from tbl_employee
        <foreach collection="ids" item="item_id" separator=","
                 open="where id in(" close=")">
            #{item_id}
        </foreach>
    </select>
</mapper>


测试代码：
package com.mybatis.demo;

import com.mybatis.bean.Employee;
import com.mybatis.dao.EmployeeMapper;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Test;

import java.io.IOException;
import java.io.InputStream;
import java.util.Arrays;
import java.util.List;

public class MyTest {
    public SqlSessionFactory getSqlSessionFactory() throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        return new SqlSessionFactoryBuilder().build(inputStream);
    }

    @Test
    public void test() throws IOException {
        SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
        SqlSession openSession = sqlSessionFactory.openSession(true);
        try {
            EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class);
            List<Employee> emps = mapper.getEmpsByConditionForeach(Arrays.asList(1, 6, 8));
            for (Employee emp : emps) {
                System.out.println(emp);
            }
        } finally {
            openSession.close();
        }
    }
}