Mybatis学习笔记14 - 动态sql之foreach标签

时间：2022-04-03 23:59:59

一、查询给定集合中员工id对应的所有员工信息

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在给定集合中的所有员工信息

    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();

        }

    }

}

二、批量保存

1、批量保存方式一示例代码

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 {

    public void addEmps(@Param("emps") List<Employee> emps);

}

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">

    <!--批量保存-->

    <!--MySQL下批量保存：可以foreach遍历   mysql支持values(),(),()语法-->

    <insert id="addEmps">

        insert into tbl_employee(last_name, email,gender, d_id)

        values

        <foreach collection="emps" item="emp" separator=",">

            (#{emp.lastName},#{emp.email},#{emp.gender},#{emp.dept.id})

        </foreach>

    </insert>

</mapper>

测试代码：

package com.mybatis.demo;

import com.mybatis.bean.Department;

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.ArrayList;

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 = new ArrayList<Employee>();

            emps.add(new Employee(null, "sujun", "sujun@qq.com", 1, new Department(1)));

            emps.add(new Employee(null, "minmin", "minmin@qq.com", 1, new Department(2)));

            mapper.addEmps(emps);

        } finally {

            openSession.close();

        }

    }

}

2、批量保存方式二示例代码

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 {

    public void addEmps(@Param("emps") List<Employee> emps);

}

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">

    <!--批量保存-->

    <!--

        这种方式需要数据库连接属性allowMultiQueries=true

	 	这种分号分隔多个sql可以用于其他的批量操作（删除，修改）

	-->

    <insert id="addEmps">

        <foreach collection="emps" item="emp" separator=";">

            insert into tbl_employee(last_name,email,gender,d_id)

            values(#{emp.lastName},#{emp.email},#{emp.gender},#{emp.dept.id})

        </foreach>

    </insert>

</mapper>

测试代码：

package com.mybatis.demo;

import com.mybatis.bean.Department;

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.ArrayList;

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 = new ArrayList<Employee>();

            emps.add(new Employee(null, "jun", "jun@qq.com", 1, new Department(1)));

            emps.add(new Employee(null, "min", "min@qq.com", 1, new Department(2)));

            mapper.addEmps(emps);

        } finally {

            openSession.close();

        }

    }

}

数据库连接配置：

jdbc.url=jdbc:mysql://localhost:3306/mybatis_demo?allowMultiQueries=true

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