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零基础学JavaWeb开发（十六）之 mybatis（1）

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导读：本篇文章讲解 零基础学JavaWeb开发（十六）之 mybatis（1），希望对大家有帮助，欢迎收藏，转发！站点地址：www.bmabk.com

二十二、mybatis

1、什么是mybatis

MyBatis中文网

mybatis是一个用Java编写的持久层框架，它使用ORM实现了结果集的封装。

ORM是Object Relational Mapping 对象关系映射。简单来说，就是把数据库表和实体类及实体类的属性对应起来，让开发者操作实体类就实现操作数据库表，它封装了jdbc操作的很多细节，使开发者只需要关注sql语句本身，而无需关注注册驱动，创建连接等复杂过程。

ORM:Object-Relation-Mapping，也就是对象关系映射，是一种程序设计思想，mybatis就是ORM的一种实现方式，简单来说就是将数据库中查询出的数据映射到对应的实体中。

数据库层框架

1.com.mayikt.servlet或者com.mayikt.controller——–控制层 springmvc

2.com.mayikt.service—业务逻辑层

3.com.mayikt.dao—-数据库访问层 hibernate或者mybatis、jpa

1.数据库连接相关配置

2.编写sql语句 jdbc 查询操作 单独取出每个值 在赋值给我们对象

mybatis、springmvc、springboot

使用mybatis orm java中 对象与数据库中表中 字段 对应

底层通过反射机制自动赋值

sql语句 自动形式得出对象

前提 orm

2、mybatis快速入门

2.1、数据库表结构

CREATE TABLE `mayikt_users` (
  `id` int NOT NULL AUTO_INCREMENT,
  `name` varchar(255) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=33 DEFAULT CHARSET=utf8mb3;

1.引入mybatis相关依赖 已经完成了

2.mybatis-config.xml（该配置文件名称是可以改） 存放就是我们数据库相关连接信息

3.定义mapper —-编写我们mybatis 相关 sql语句 每个表 对应一个mapper

4.定义java对象–需要注意下 类中的 成员属性与数据库表中字段 映射 默认 类中的 成员属性数据库表中字段名称对应的。

5.使用 mybatis api开始执行该 sql语句即可 得到结果

2.2、maven依赖

        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.4.5</version>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.18</version>
        </dependency>

2.3、定义xml配置文件

存放数据库连接信息mybatis-config.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://127.0.0.1:3306/mayikt?serverTimezone=GMT%2B8"/>
                <property name="username" value="root"/>
                <property name="password" value="root"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="mybatis/userMaaper.xml"/>
    </mappers>
</configuration>

2.4、Mapper文件

<?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="userMapper">
    <select id="getByUsers" resultType="com.mayikt.entity.UserEntity">
        select * from mayikt_users
  </select>
</mapper>

2.5、测试代码

package com.mayikt.test;

import com.mayikt.entity.UserEntity;
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 java.io.IOException;
import java.io.InputStream;
import java.util.List;


public class Test01 {
    public static void main(String[] args) throws IOException {
        // 1.读取加载mybatis-config.xml
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        // 2.获取到获取到
        SqlSession sqlSession = sqlSessionFactory.openSession();
        // 3.根据 mapper id=getByUsers 执行该s  ql 语句 通过  sql语句得到我们的对象 orm
        List<UserEntity> userEntitys = sqlSession.selectList("getByUsers", UserEntity.class);
        System.out.println(userEntitys);
        sqlSession.close();
    }
}

package com.mayikt.test;

import com.mayikt.entity.UserEntity;
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 java.io.IOException;
import java.io.InputStream;
import java.util.List;


public class Test01 {
    public static void main(String[] args) throws IOException {
        // 1.读取加载mybatis-config.xml
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        // 2.获取到获取到
        SqlSession sqlSession = sqlSessionFactory.openSession();
        // 3.根据 mapper id=getByUsers 执行该s  ql 语句 通过  sql语句得到我们的对象 orm
        List<UserEntity> userEntitys = sqlSession.selectList("getByUsers", UserEntity.class);
        System.out.println(userEntitys);
        sqlSession.close();
    }
}

3、mapper代理开发模式

1.mapper接口方式开发整合就必须是对应的mapper接口的全限定类名

2.接口中的方法与映射文件中的SQL语句的ID

3.需要在mybatis-config.xml 新增 加载该userMaaper

    <mappers>
        <mapper resource="mybatis/userMapper.xml"/>
    </mappers>
4.定义mapper 接口 需要考虑方法的名称与userMapper.xml的 sql id名称保持一致。
package com.mayikt.mapper;

import com.mayikt.entity.UserEntity;

import java.util.List;


public interface UserMapper {
    List<UserEntity> getByUsers();
}

<?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.mayikt.mapper.UserMapper">
    <select id="getByUsers" resultType="com.mayikt.entity.UserEntity">
        select * from mayikt_users
  </select>
</mapper>

5.相关代码

package com.mayikt.test;

import com.mayikt.entity.UserEntity;
import com.mayikt.mapper.UserMapper;
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 java.io.IOException;
import java.io.InputStream;
import java.util.List;

public class Test01 {
    public static void main(String[] args) throws IOException {
        // 1.读取加载mybatis-config.xml
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        // 2.获取到获取到
        SqlSession sqlSession = sqlSessionFactory.openSession();
        // 3.根据 mapper id=getByUsers 执行该s  ql 语句 通过  sql语句得到我们的对象 orm
//        List<UserEntity> userEntitys = sqlSession.selectList("getByUsers", UserEntity.class);
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        System.out.println(mapper.getByUsers());
//        System.out.println(userEntitys);
        sqlSession.close();
    }
}

4、mybatis增删改查

CREATE TABLE `mayikt_flight` (
  `id` int NOT NULL AUTO_INCREMENT COMMENT 'id列',
  `flight_id` varchar(20) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL COMMENT '航号',
  `company` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL COMMENT '航空公司',
  `departure_airport` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL COMMENT '出发机场',
  `arrive_airport` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL COMMENT '达到机场',
  `departure_time` datetime DEFAULT NULL COMMENT '出发时间',
  `arrive_time` datetime DEFAULT NULL COMMENT '到达时间',
  `model` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL COMMENT '机型',
  `is_delete` int DEFAULT NULL COMMENT '是否隐藏0显示 1隐藏',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=16 DEFAULT CHARSET=utf8mb3;

4.1、查询所有数据

package com.mayikt.entity;

import java.util.Date;

public class FlightEntity {
    private Integer id;
    private String flightId;
    private String company;
    private String departureAirport;
    private String arriveAirport;
    private Date departureTime;
    private Date arriveTime;
    private String model;
    private Integer isDelete;

    @Override
    public String toString() {
        return "FlightEntity{" +
                "id=" + id +
                ", flightId='" + flightId + '\'' +
                ", company='" + company + '\'' +
                ", departureAirport='" + departureAirport + '\'' +
                ", arriveAirport='" + arriveAirport + '\'' +
                ", departureTime=" + departureTime +
                ", arriveTime=" + arriveTime +
                ", model='" + model + '\'' +
                ", isDelete=" + isDelete +
                '}';
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getFlightId() {
        return flightId;
    }

    public void setFlightId(String flightId) {
        this.flightId = flightId;
    }

    public String getCompany() {
        return company;
    }

    public void setCompany(String company) {
        this.company = company;
    }

    public String getDepartureAirport() {
        return departureAirport;
    }

    public void setDepartureAirport(String departureAirport) {
        this.departureAirport = departureAirport;
    }

    public String getArriveAirport() {
        return arriveAirport;
    }

    public void setArriveAirport(String arriveAirport) {
        this.arriveAirport = arriveAirport;
    }

    public Date getDepartureTime() {
        return departureTime;
    }

    public void setDepartureTime(Date departureTime) {
        this.departureTime = departureTime;
    }

    public Date getArriveTime() {
        return arriveTime;
    }

    public void setArriveTime(Date arriveTime) {
        this.arriveTime = arriveTime;
    }

    public String getModel() {
        return model;
    }

    public void setModel(String model) {
        this.model = model;
    }

    public Integer getIsDelete() {
        return isDelete;
    }

    public void setIsDelete(Integer isDelete) {
        this.isDelete = isDelete;
    }
}


package com.mayikt.mapper;

import com.mayikt.entity.FlightEntity;

import java.util.List;

public interface FlightMapper {
    /**
     * 查询
     * 1.查询所有
     * 2.根据条件查询
     * 3.动态查询方式
     */
    List<FlightEntity> getByFlightAll();

}
package com.mayikt.service;

import com.mayikt.entity.FlightEntity;
import com.mayikt.mapper.FlightMapper;
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 java.io.IOException;
import java.io.InputStream;
import java.util.List;

public class FlightService {
    private FlightMapper flightMapper;

    public FlightService() throws IOException {
        // 通过无参构造方法 初始化mybatis 得到flightMapper
        // mybatis-config.xml 目录位置
        String resource = "mybatis-config.xml";
        // 1.解析mybatis-config.xml 得到数据库相关的配置信息
        InputStream inputStream = Resources.getResourceAsStream(resource);
        //2.创建得到一个sqlSessionFactory
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        //3.获取到sqlSession
        SqlSession sqlSession = sqlSessionFactory.openSession();
        flightMapper = sqlSession.getMapper(FlightMapper.class);
//        sqlSession.close();
    }
}

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<!-- 数据库相关的配置-->
<configuration>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://127.0.0.1:3306/flight?serverTimezone=GMT%2B8"/>
                <property name="username" value="root"/>
                <property name="password" value="root"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="mybatis/flightMapper.xml"/>
    </mappers>
</configuration>



<?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">
<!-- namespace=-->
<mapper namespace="com.mayikt.mapper.FlightMapper">
    <select id="getByFlightAll" resultType="com.mayikt.entity.FlightEntity">
            select *
     from mayikt_flight;
  </select>


</mapper>

4.1.1、解决数据库与类中成员属性不一致性

方式1：

使用 sql语句 as的方法 代码会非常重复。

<?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">
<!-- namespace=-->
<mapper namespace="com.mayikt.mapper.FlightMapper">
    <select id="getByFlightAll" resultType="com.mayikt.entity.FlightEntity">
            select  id as id,flight_id as flightId,
     company as company, departure_airport as departureAirport
,arrive_airport as  arriveAirport, departure_time as departureTime
,arrive_time as  arriveTime,model as model,is_delete as
isDelete
     from mayikt_flight;

  </select>

</mapper>

方式2：

resultMap 定义数据库表中字段名称与类中成员属性名称 关联映射

数据库字段：flight_id—-类中成员名称 flightId

<?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">
<!-- namespace=-->
<mapper namespace="com.mayikt.mapper.FlightMapper">
    <resultMap id="flightEntityMap" type="com.mayikt.entity.FlightEntity">
        <!-- 数据库中字段名称 column="" property="id"  类中成员属性名称-->
        <id column="id" property="id"></id>
        <result column="flight_id" property="flightId"></result>
        <result column="departure_airport" property="departureAirport"></result>
        <result column="departure_time" property="departureTime"></result>
        <result column="arrive_time" property="arriveTime"></result>
        <result column="model" property="model"></result>
        <result column="is_delete" property="isDelete"></result>
    </resultMap>
    <select id="getByFlightAll" resultType="com.mayikt.entity.FlightEntity">
            select  id as id,flight_id as flightId,
     company as company, departure_airport as departureAirport
,arrive_airport as  arriveAirport, departure_time as departureTime
,arrive_time as  arriveTime,model as model,is_delete as
isDelete
     from mayikt_flight;
  </select>

    <!--  定义数据库中字段名称与我们 类中成员属性值 关联映射-->
    <select id="getByFlightAll2" resultMap="flightEntityMap">
            select * from mayikt_flight where  id=10;
  </select>
</mapper>

4.2、id查询数据

    /**
     * 就是根据主键id查询数据
     */
    FlightEntity getByIdFlight(Integer id);
 
    public FlightEntity getByIdFlight(Integer id) {
        return flightMapper.getByIdFlight(id);
    }
    <!--
    parameterType int string Double 自定义对象类型 有处理防止sql语句攻击功能
    -->
    <select id="getByIdFlight" parameterType="int" resultMap="flightEntityMap">
            select * from mayikt_flight where  id=#{id};
  </select>

4.3、插入数据

    /**
     * 插入数据的结果 如果影响行数 大于0 成功的  否则 就是失败的
     *
     * @param FlightEntity FlightEntity
     * @return
     */
    int insertFlight(FlightEntity flightEntity);

    private FlightMapper flightMapper;
    private SqlSession sqlSession;

    public FlightService() throws IOException {
        // 通过无参构造方法 初始化mybatis 得到flightMapper
        // mybatis-config.xml 目录位置
        String resource = "mybatis-config.xml";
        // 1.解析mybatis-config.xml 得到数据库相关的配置信息
        InputStream inputStream = Resources.getResourceAsStream(resource);
        //2.创建得到一个sqlSessionFactory
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        //3.获取到sqlSession
        sqlSession = sqlSessionFactory.openSession();
        flightMapper = sqlSession.getMapper(FlightMapper.class);
//        sqlSession.close();
    }

    public List<FlightEntity> getByFlightAll() {
        return flightMapper.getByFlightAll();
    }


    public FlightEntity getByIdFlight(Integer id) {
        return flightMapper.getByIdFlight(id);
    }

    public int insertFlight(FlightEntity flightEntity) {
        int result = flightMapper.insertFlight(flightEntity);
        // 需要提交事务事务的
        sqlSession.commit();// 提交事务
        return result;
    }
    <!--
    select标签查询数据
    insert标签 插入数据
    -->
    <insert id="insertFlight" parameterType="com.mayikt.entity.FlightEntity">
        INSERT INTO `flight`.`mayikt_flight` (`id`, `flight_id`, `company`, `departure_airport`, `arrive_airport`, `departure_time`, `arrive_time`, `model`, `is_delete`)
        VALUES (null,  #{flightId}, #{company}, #{departureAirport},#{arriveAirport}, #{departureTime},#{arriveTime},#{model}, #{isDelete});
    </insert>

4.4、修改数据

    int updateFlight(FlightEntity flightEntity);
    public int updateFlight(FlightEntity flightEntity) {
        int result = flightMapper.updateFlight(flightEntity);
        // 需要提交事务事务的  数据增加 update  删除
        sqlSession.commit();// 提交事务
        return result;
    }

    <update id="updateFlight" parameterType="com.mayikt.entity.FlightEntity">
        UPDATE `flight`.`mayikt_flight` SET `id`=#{id}, `flight_id`=#{flightId}, `company`=#{company},
         `departure_airport`=#{departureAirport},
         `arrive_airport`=#{arriveAirport}, `departure_time`=#{departureTime},
         `arrive_time`=#{arriveTime}, `model`=#{model}, `is_delete`=#{isDelete} WHERE (`id`=#{id});
    </update>

4.5、删除数据


    int deleteByIdFlight(Integer id);
    public int deleteByIdFlight(Integer id) {
        int result = flightMapper.deleteByIdFlight(id);
        // 需要提交事务事务的  数据增加 update  删除
        sqlSession.commit();// 提交事务
        return result;
    }

    <delete id="deleteByIdFlight" parameterType="int">
       delete from mayikt_flight where id=#{id};
    </delete>

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