MyBatis从入门到“入土“

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一、Mybatis为何物？👌

二、快速入门🤣

1、新建项目😊

2、数据库建表😊

3、导入依赖的jar包😊

4、根据表建pojo类😊

5、编写mapper映射文件（编写sql）😊

6、编写全局配置文件(主要是配置数据源信息)😊

7、测试😊

三、快速入土😢

代理开发😂

1、定义与SQL映射文件同名的Mapper接口，并且将Mapper接口和SQL映射文件放置在同一目录下。

2、设置SQL映射文件的namespace属性为Mapper接口全限定名。

3、在Mapper接口中定义方法，方法名就是SQL映射文件中sql语句的id，并保持参数类型和返回值类型一致。

4、通过SqlSession的getMapper方法获取Mapper接口的代理对象，并调用对应方法。

Mybatis核心配置--mybatis-config.xml😂

1、可以连接多个数据库

2、配置标签

案例😂

1、建表

2、实体类

3、测试类

4、mybatisx插件

根据方法自动生成mapper映射文件

5、查询（查询所有）

6、查看详情（根据id查询一个）

7、条件查询

根据参数接收（无参/一个参数/两个参数/）

散装参数（模糊匹配）

对象参数

map参数

动态条件查询（用户输入条件时，是否所有条件都会填写。不是，哥们🤣👌）

使用if，choose，when设定条件

8、添加

主键返回

9、修改

修改全部字段

修改动态字段

10、删除

单个删除

批量删除

注解开发😍

一、Mybatis为何物？👌

🤦‍♂️恶臭的描述： MyBatis 是一个优秀的持久层框架，它对JDBC的操作数据库的过程进行封装，让开发者只需要关注 SQL 本身，而不需要花费精力去处理例如注册驱动、创建connection、创建statement、手动设置参数、结果集检索等JDBC繁琐的过程代码。

❤️舒服的描述：

不需要手动编写 JDBC 代码来执行 SQL 语句，也不需要处理数据库连接的创建和关闭。

所有的数据库操作都被抽象成了简单的 Mapper 方法调用。（伟大无需多言！）

Mybatis中文官网

二、快速入门🤣

前言：

完整结构图

只需要通过如下几个步骤，即可用mybatis快速进行持久层的开发

编写全局配置文件
编写mapper映射文件
加载全局配置文件，生成SqlSessionFactory
创建SqlSession，调用mapper映射文件中的SQL语句来执行CRUD操作

🤣话不多说，直接Mybatis启动！🤣

1、新建项目😊

java8

2、数据库建表😊

3、导入依赖的jar包😊

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd"><modelVersion>4.0.0</modelVersion><groupId>org.itqingshui</groupId><artifactId>mybatis-test1</artifactId><version>1.0-SNAPSHOT</version><name>Archetype - mybatis-test1</name><url>http://maven.apache.org</url><dependencies><dependency><groupId>org.mybatis</groupId><artifactId>mybatis</artifactId><version>3.5.6</version></dependency><dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId><version>8.0.21</version></dependency><dependency><groupId>org.projectlombok</groupId><artifactId>lombok</artifactId><version>1.18.30</version></dependency></dependencies><build><plugins><plugin><groupId>org.apache.maven.plugins</groupId><artifactId>maven-compiler-plugin</artifactId><version>3.8.1</version><configuration><source>1.8</source> <!-- 替换为你的JDK版本 --><target>1.8</target> <!-- 替换为你的JDK版本 --></configuration></plugin></plugins></build></project>

4、根据表建pojo类😊

package pojo;import lombok.*;@Getter
@Setter
@NoArgsConstructor
@AllArgsConstructor
@ToString
public class Student{private Integer id;private String name;private Integer score;private Integer age;private Integer gender;
}

@Getter
@Setter：省略set，get方法。

@NoArgsConstructor：建立一个无参构造器。

@AllArgsConstructor：建立一个全参构造器。

@ToString：建立一个tostring方法。

5、编写mapper映射文件（编写sql）😊

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapperPUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="pojo.StudentMapper"><select id="findAll" resultType="pojo.Student">select * from student</select><insert id="insert" parameterType="pojo.Student">insert into student(name,gender,age,score) values(#{name},#{gender},#{age},#{score})</insert><delete id="delete" parameterType="int">delete from student where id=#{id}</delete><update id="update" parameterType="pojo.Student">update student set name=#{name},gender=#{gender},age=#{age},score=#{score} where id=#{id}</update></mapper>

6、编写全局配置文件(主要是配置数据源信息)😊

resources包下

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configurationPUBLIC "-//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://localhost:3306/ssm?useSSL=false&amp;serverTimezone=UTC"/><property name="username" value="lovertx"/><property name="password" value="1234567"/></dataSource></environment></environments><mappers><!-- 加载编写的SQL语句 --><mapper resource="StudentMapper.xml"/></mappers>
</configuration>

7、测试😊

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 pojo.Student;import java.io.IOException;
import java.io.InputStream;
import java.util.List;public class MybatisDemo {public static void main(String[] args) throws IOException, ClassNotFoundException {String resource = "mybatis-config.xml";InputStream inputStream = Resources.getResourceAsStream(resource);SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);SqlSession sqlSession = sqlSessionFactory.openSession();List<Student> student = sqlSession.selectList("pojo.StudentMapper.findAll");for (Student s : student){System.out.println(s);}sqlSession.close();}
}

三、快速入土😢

代理开发😂

对于

  List<Student> student = sqlSession.selectList("pojo.StudentMapper.findAll");

目的：

解决原生方式中的硬编码。

简化后期执行SQL

1、定义与SQL映射文件同名的Mapper接口，并且将Mapper接口和SQL映射文件放置在同一目录下。

在resources包下创建mapper包并放入StudentMapper.xml

2、设置SQL映射文件的namespace属性为Mapper接口全限定名。

将

<mapper namespace="pojo.StudentMapper">

改为

<mapper namespace="mapper.StudentMapper">

3、在Mapper接口中定义方法，方法名就是SQL映射文件中sql语句的id，并保持参数类型和返回值类型一致。

StudentMapper中

package mapper;import pojo.Student;import java.util.List;public interface StudentMapper {List<Student>  findAll();
}

4、通过SqlSession的getMapper方法获取Mapper接口的代理对象，并调用对应方法。

StudentMapper userMapper = sqlSession.getMapper(StudentMapper.class);
userMapper.findAll().forEach(System.out::println);

Mybatis核心配置--mybatis-config.xml😂

1、可以连接多个数据库

可以配置多个environment，通过default属性切换不同的environment

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configurationPUBLIC "-//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://localhost:3306/ssm?useSSL=false&amp;serverTimezone=UTC"/><property name="username" value="lovertx"/><property name="password" value="1234567"/></dataSource></environment></environments><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://localhost:3306/ssm?useSSL=false&amp;serverTimezone=UTC"/><property name="username" value="lovertx"/><property name="password" value="1234567"/></dataSource></environment></environments><mappers><!-- 加载编写的SQL语句 --><mapper resource="mapper/StudentMapper.xml"/></mappers>
</configuration>

2、配置标签

案例😂

1、建表

id：主键

brand_name:品牌名称

company_name:企业名称

ordered:排序字段

description:描述信息

status:状态（0：禁用，1启用）

2、实体类

package pojo;import lombok.*;@Setter
@Getter
@NoArgsConstructor
@AllArgsConstructor
@ToString
public class Brand {private Integer id;private String brand_name;private String company_name;private Integer ordered;private String description;private Integer status;
}

3、测试类

4、mybatisx插件

通过点击左边的红色小鸟

可以找到蓝色小鸟

根据方法自动生成mapper映射文件

1、第一步：在StudentMapper中

package mapper;import pojo.Student;import java.util.List;public interface StudentMapper {List<Student>  findAll();Student findById(int id);
}

2、使用插件自动生成

<select id="findById" resultType="pojo.Student"></select>

3、补充实际操作

<select id="findById" resultType="pojo.Student">select * from student where id=#{id}</select>

5、查询（查询所有）

1、创建BrandMapper（先写方法，后自动写sql）

package mapper;import pojo.Brand;
import java.util.List;public interface BrandMapper {List<Brand> findAll();
}

2、创建BrandMapper.xml

package mapper;import pojo.Brand;
import java.util.List;public interface BrandMapper {List<Brand> findAll();
}

3、配置映射文件

在mybatis-config.xml添加 <mapper resource="mapper/BrandMapper.xml"/>

<mappers><!-- 加载编写的SQL语句 --><mapper resource="mapper/StudentMapper.xml"/><mapper resource="mapper/BrandMapper.xml"/></mappers>

4、测试类

import mapper.BrandMapper;
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;public class MybatisDemo3 {public static void main(String[] args) throws IOException, ClassNotFoundException {String resource = "mybatis-config.xml";InputStream inputStream = Resources.getResourceAsStream(resource);SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);SqlSession sqlSession = sqlSessionFactory.openSession();BrandMapper userMapper = sqlSession.getMapper(BrandMapper.class);userMapper.findAll().forEach(System.out::println);sqlSession.close();}
}

6、查看详情（根据id查询一个）

BrandMapper中写：

Brand findById(int id);

public interface BrandMapper {List<Brand> findAll();Brand findById(int id);
}

BrandMapper.xml中写：

<select id="findById" resultType="pojo.Brand">select * from tb_brand where id = #{id}</select>

测试类中写：

public class MybatisDemo {public static void main(String[] args) throws IOException, ClassNotFoundException {String resource = "mybatis-config.xml";InputStream inputStream = Resources.getResourceAsStream(resource);SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);SqlSession sqlSession = sqlSessionFactory.openSession();BrandMapper brandMapper = sqlSession.getMapper(BrandMapper.class);Brand brand = brandMapper.findById(1);System.out.println(brand);sqlSession.close();}
}

7、条件查询

类似于实现这样的功能：

根据参数接收（无参/一个参数/两个参数/）

散装参数（模糊匹配）

因模糊匹配需要处理参数

接口方法

List<Brand> selectByCondition(@Param("status") int status, @Param("company_name") String company_name, @Param("brand_name") String brand_name);

sql语句

<select id="selectByCondition" resultType="pojo.Brand">select * from tb_brandwhere status = #{status}and brand_name like #{brand_name}and company_name like #{company_name}</select>

测试类

public class MybatisDemo {public static void main(String[] args) throws IOException {//接收参数int status = 1;String company_name = "华为";String brand_name = "华为";//因模糊匹配，所有处理参数company_name = "%" + company_name + "%";brand_name = "%" + brand_name + "%";String resource = "mybatis-config.xml";InputStream inputStream = Resources.getResourceAsStream(resource);SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);SqlSession sqlSession = sqlSessionFactory.openSession();BrandMapper brandMapper = sqlSession.getMapper(BrandMapper.class);List<Brand> brands = brandMapper.selectByCondition(status, company_name, brand_name);for (Brand brand : brands) {System.out.println(brand);}sqlSession.close();}
}

对象参数

对象的属性名称要和参数占位符名称一致

Mapper接口：

List<Brand> selectByCondition(Brand brand);

sql语句：

<select id="selectByCondition" resultType="pojo.Brand">select * from tb_brandwhere status = #{status}and brand_name like #{brand_name}and company_name like #{company_name}</select>

测试类：

多了个封装对象

public class MybatisDemo {public static void main(String[] args) throws IOException {//接收参数int status = 1;String company_name = "华为";String brand_name = "华为";//因模糊匹配，所有处理参数company_name = "%" + company_name + "%";brand_name = "%" + brand_name + "%";//封装对象Brand brand = new Brand();brand.setStatus(status);brand.setCompany_name(company_name);brand.setBrand_name(brand_name);String resource = "mybatis-config.xml";InputStream inputStream = Resources.getResourceAsStream(resource);SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);SqlSession sqlSession = sqlSessionFactory.openSession();BrandMapper brandMapper = sqlSession.getMapper(BrandMapper.class);//      List<Brand> brands = brandMapper.selectByCondition(status, company_name, brand_name);List<Brand> brands = brandMapper.selectByCondition(brand);for (Brand brand1 : brands) {System.out.println(brand1);}sqlSession.close();}
}

map参数

Mapper接口：

List<Brand> selectByCondition(Map map);

sql语句：

<select id="selectByCondition" resultType="pojo.Brand">select * from tb_brandwhere status = #{status}and brand_name like #{brand_name}and company_name like #{company_name}</select>

测试类：

public class MybatisDemo {public static void main(String[] args) throws IOException {//接收参数int status = 1;String company_name = "华为";String brand_name = "华为";//因模糊匹配，所有处理参数company_name = "%" + company_name + "%";brand_name = "%" + brand_name + "%";//封装对象
//        Brand brand = new Brand();
//        brand.setStatus(status);
//        brand.setCompany_name(company_name);
//        brand.setBrand_name(brand_name);Map map = new HashMap();map.put("status",status);map.put("company_name",company_name);map.put("brand_name",brand_name);String resource = "mybatis-config.xml";InputStream inputStream = Resources.getResourceAsStream(resource);SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);SqlSession sqlSession = sqlSessionFactory.openSession();BrandMapper brandMapper = sqlSession.getMapper(BrandMapper.class);//      List<Brand> brands = brandMapper.selectByCondition(status, company_name, brand_name);
//      List<Brand> brands = brandMapper.selectByCondition(brand);List<Brand> brands = brandMapper.selectByCondition(map);for (Brand brand1 : brands) {System.out.println(brand1);}sqlSession.close();}
}

动态条件查询（用户输入条件时，是否所有条件都会填写。不是，哥们🤣👌）

只需要修改sql语句：

<select id="selectByCondition" resultType="pojo.Brand">select * from tb_brandwhere<if test="status != null">status = #{status}</if><if test="brand_name != null and brand_name != ''">and brand_name like #{brand_name}</if><if test="company_name != null and company_name != ''">and company_name like #{company_name}</if></select>

可是当特殊条件缺少时会出现错误：

 Map map = new HashMap();//map.put("status",status);map.put("company_name",company_name);//map.put("brand_name",brand_name);

解决：恒等式

将sql语句修改为：

<select id="selectByCondition" resultType="pojo.Brand">select * from tb_brand<where><if test="status != null">and status = #{status}</if><if test="brand_name != null and brand_name != ''">and brand_name like #{brand_name}</if><if test="company_name != null and company_name != ''">and company_name like #{company_name}</if></where></select>

使用if，choose，when设定条件

<select id="selectByConditionOne" resultType="pojo.Brand">select * from tb_brandwhere<choose><!--相当于switch--><when test="status != null"><!--相当于case-->status = #{status}</when><when test="brand_name != null and brand_name != ''">brand_name like #{brand_name}</when><when test="company_name != null and company_name != ''">company_name like #{company_name}</when><otherwise><!--当用户一个条件都不给-->1=1</otherwise></choose></select>

8、添加

接口方法

void add(Brand brand);

sql语句

<insert id="add">insert into tb_brand(brand_name,company_name,ordered,description,status)values(#{brand_name},#{company_name},#{ordered},#{description},#{status})</insert>

测试类

public class MybatisDemo3 {public static void main(String[] args) throws IOException, ClassNotFoundException {String resource = "mybatis-config.xml";InputStream inputStream = Resources.getResourceAsStream(resource);SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);SqlSession sqlSession = sqlSessionFactory.openSession();BrandMapper userMapper = sqlSession.getMapper(BrandMapper.class);int status = 1;String company_name = "菠萝手机";String brand_name = "菠萝";int ordered = 1;String description = "美国有苹果，中国有菠萝";Brand brand = new Brand();brand.setStatus(status);brand.setCompany_name(company_name);brand.setBrand_name(brand_name);brand.setOrdered(ordered);brand.setDescription(description);userMapper.add(brand);
//事务提交sqlSession.commit();sqlSession.close();}
}

主键返回

实现可查询主键id的值

因为事务回滚导致少了id=4

因此查询菠萝的id的值为5

将sql语句改为

<insert id="add" useGeneratedKeys="true" keyProperty="id">insert into tb_brand(brand_name,company_name,ordered,description,status)values(#{brand_name},#{company_name},#{ordered},#{description},#{status})</insert>

即添加

useGeneratedKeys="true" keyProperty="id"

9、修改

修改全部字段

实现

Mapper接口

void update(Brand brand);

SQL语句

<update id="update">update tb_brand<set><if test="brand_name != null and brand_name != ''">brand_name = #{brand_name},</if><if test="company_name != null and company_name != ''">company_name = #{company_name},</if><if test="ordered != null">ordered = #{ordered},</if><if test="description != null and description != ''">description =#{description},status = #{status}</if>where id = #{id}</set></update>

测试类

public class UpdateTest {public static void main(String[] args) throws IOException{String resource = "mybatis-config.xml";InputStream inputStream = Resources.getResourceAsStream(resource);SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);SqlSession sqlSession = sqlSessionFactory.openSession(true);BrandMapper brandMapper = sqlSession.getMapper(BrandMapper.class);Brand brand = new Brand();brand.setId(5);brand.setBrand_name("香飘飘");brand.setCompany_name("香飘飘");brand.setDescription("香飘飘");brand.setOrdered(100);brand.setStatus(1);brandMapper.update(brand);sqlSession.close();}
}

修改动态字段

实现修改密码功能（想单独改哪个值就改哪个值）

如果调用接口却不给参数，则数据库会出现null值🤦‍♂️

实现

只需要在SQL语句中添加条件，添加<set>标签

<update id="update">update tb_brand<set><if test="brand_name != null and brand_name != ''">brand_name = #{brand_name},</if><if test="company_name != null and company_name != ''">company_name = #{company_name},</if><if test="ordered != null">ordered = #{ordered},</if><if test="description != null and description != ''">description =#{description},status = #{status}</if>where id = #{id}</set></update>

10、删除

单个删除

Mapper接口

void delete(int id);

SQL语句

<delete id="delete">delete from tb_brand where id = #{id}</delete>

测试类

public class DeleteTest {public static void main(String[] args) throws IOException, IOException {String resource = "mybatis-config.xml";InputStream inputStream = Resources.getResourceAsStream(resource);SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);SqlSession sqlSession = sqlSessionFactory.openSession(true);BrandMapper brandMapper = sqlSession.getMapper(BrandMapper.class);brandMapper.delete(2);sqlSession.close();}
}

批量删除

实现

传id数组，sql遍历数组，一个一个删掉

Mapper接口

void deleteByIds(@Param("ids") int[] ids);

SQL语句

<delete id="deleteByIds">delete from tb_brand where id in<foreach collection="ids" item="id" open="(" separator="," close=")">#{id}</foreach></delete>

测试类

public class DeleteTest2 {public static void main(String[] args) throws IOException, IOException {String resource = "mybatis-config.xml";InputStream inputStream = Resources.getResourceAsStream(resource);SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);SqlSession sqlSession = sqlSessionFactory.openSession(true);BrandMapper brandMapper = sqlSession.getMapper(BrandMapper.class);int []ids = {5,6};brandMapper.deleteByIds(ids);sqlSession.close();}
}

注解开发😍

优点：对于简单的SQL语句使用注解开发会非常便捷。

@Select("select * from tb_user where id = #{id}")
public User selectById(int id);

查询：@Select

添加：@Insert

修改: @Update

删除：@Delete

缺点：对于复杂的SQL语句应使用xml映射文件编写。

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapperPUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="mapper.BrandMapper"><insert id="add" useGeneratedKeys="true" keyProperty="id">insert into tb_brand(brand_name,company_name,ordered,description,status)values(#{brand_name},#{company_name},#{ordered},#{description},#{status})</insert><update id="update">update tb_brand<set><if test="brand_name != null and brand_name != ''">brand_name = #{brand_name},</if><if test="company_name != null and company_name != ''">company_name = #{company_name},</if><if test="ordered != null">ordered = #{ordered},</if><if test="description != null and description != ''">description =#{description},status = #{status}</if>where id = #{id}</set></update><delete id="delete">delete from tb_brand where id = #{id}</delete><delete id="deleteByIds">delete from tb_brand where id in<foreach collection="ids" item="id" open="(" separator="," close=")">#{id}</foreach></delete><select id="findAll" resultType="pojo.Brand">select * from tb_brand</select><select id="findById" resultType="pojo.Brand">select * from tb_brand where id = #{id}</select><!--    <select id="selectByCondition" resultType="pojo.Brand">-->
<!--        select * from tb_brand-->
<!--        where status = #{status}-->
<!--            and brand_name like #{brand_name}-->
<!--            and company_name like #{company_name}-->
<!--    </select>--><select id="selectByCondition" resultType="pojo.Brand">select * from tb_brand<where><if test="status != null">and status = #{status}</if><if test="brand_name != null and brand_name != ''">and brand_name like #{brand_name}</if><if test="company_name != null and company_name != ''">and company_name like #{company_name}</if></where></select><select id="selectByConditionOne" resultType="pojo.Brand">select * from tb_brandwhere<choose><!--相当于switch--><when test="status != null"><!--相当于case-->status = #{status}</when><when test="brand_name != null and brand_name != ''">brand_name like #{brand_name}</when><when test="company_name != null and company_name != ''">company_name like #{company_name}</when><otherwise><!--当用户一个条件都不给-->1=1</otherwise></choose></select>
</mapper>