MyBatis

什么是MyBatis

MyBatis是一款优秀的持久层框架，用于简化JDBC开发
- 持久层

负责将数据到保存到数据库的那一层代码

JavaEE三层架构：表现层、业务层、持久层

MyBatis快速入门/Mapper代理开发

使用MyBatis查询表中的所有信息

（1）安装MyBatis

<dependency>
    <groupId>org.mybatis</groupId>
    <artifactId>mybatis</artifactId>
    <version>3.4.6</version>
</dependency>

（2）创建mybatis核心配置文件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">
                <!--数据连接信息-->
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql:///mybatis?useSSL=false"/>
                <property name="username" value="root"/>
                <property name="password" value="510609"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <!--加载SQL映射-->
        <mapper resource="com/UserMapper.xml"/>
    </mappers>
</configuration>

（3）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

UserMapper.java****：

package com.dome;
import pojo.User;

import java.util.List;

public interface UserMapper {
    List<User> selectAll();
}

resultType：可选pojo，预计返回值类型

id是接口中的方法名

设置SQL映射的namespace属性为Mapper接口全限定名

<?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：名称空间
-->
<mapper namespace="com.dome.UserMapper">
    <select id="selectAll" resultType="pojo.User">
        select * from tb_user;
    </select>
</mapper>

（4）在实体类中调用

public class MyBatisDemo {
  public static void main(String[] args) throws IOException {
        /*1.加载mybatis的核心配置文件，获取SqlSessionFactory*/
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);


        /*2.获取SqlSessionFactory对象，用它来执行sql*/
        SqlSession sqlSession=sqlSessionFactory.openSession();

        /*3.执行sql*/
        UserMapper userMapper=sqlSession.getMapper(UserMapper.class);
		List<User> users=userMapper.selectAll();

        System.out.println(users);

        /*4.释放资源*/
        sqlSession.close();
    }
}

MyBatis核心配置文件设置

：配置数据库连接环境信息，可以配置多个environment，通过default属性切换不同的environment

：指定一个包名，MyBatis 会在包名下面搜索需要的 Java Bean

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<typeAliases>
	<package name="com.demo.pojo"/>
</typeAliases>

MyBatis之查询

接口：

public interface BrandMapper {
    /*查询所有*/
    String selectById();
}

sql语句设置：

<mapper namespace="com.demo.mapper.BrandMapper">
    <select id="selectById" resultType="String">
       select brandName from tb_brand where id=#{id}
    </select>
</mapper>

获取返回值

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BrandMapper brandMapper=sqlSession.getMapper(BrandMapper.class);
 
String brand= brandMapper.selectById(id);

多条件查询

接口这样写：

1	List<Brand> selectByCondition(@Param("status") int status,@Param("companyName") String companyName,@Param("brandName") String brandName);

SQL语句设置：

<mapper namespace="com.demo.mapper.BrandMapper">   
<!--多条件/模糊查询-->
    <select id="selectByCondition" resultType="Brand">
        select * from tb_brand
        where status = #{status}
        and companyName like #{companyName}
        and brandName like #{brandName}
    </select>
</mapper>

获取查询到的数据：

int status=1;
String companyName="华为";
String brandName="华为";
/*处理参数*/
companyName="%"+companyName+"%";
brandName="%"+brandName+"%";
 
 
 
List<Brand> list=brandMapper.selectByCondition(status,companyName,brandName);
System.out.println(list);

选择性多条件查询

在日常使用中，有时候可能用户不会填写所有的条件，而是选填一部分对此可以：

sql语句：

if标签判断是否为空

where用来解决and造成的问题

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

单条件查询

在使用时经常使用下拉列表进行单项查询，所以使用类似于switch进行选择判断

<select id="selectByCondition" resultType="Brand">
select * from tb_brand
        <where>
    <choose>        /*类似于switch*/
        <when test="status!=null">    /*类似于case选项*/
            status = #{status}
        </when>
        <when test="companyName!=null and companyName!='' ">
            and companyName like #{companyName}
        </when>
        <when test="brandName!=null and brandName!='' ">
            and brandName like #{brandName}
        </when>
        <otherwise>    /*类似于default*/
            1=1
        </otherwise>
    </choose>
     </where>
</select>

添加元素

接口添加：

1	void add(Brand brand);

sql语句：

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

添加数据：

      int status=1;
      String companyName="Samsung";
      String brandName="三星";
      String description="手机中的战斗机";
      int ordered=100;

      /*封装对象*/
      Brand brand=new Brand();
      brand.setStatus(status);
      brand.setCompanyName(companyName);
      brand.setBrandName(brandName);
      brand.setDescription(description);
      brand.setOrdered(ordered);
 
String resource = "mybatis-config.xml";
      InputStream inputStream = Resources.getResourceAsStream(resource);
      SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);

      SqlSession sqlSession=sqlSessionFactory.openSession();

      /*获取UserMapper的接口的代理对象*/
      BrandMapper brandMapper=sqlSession.getMapper(BrandMapper.class);
      brandMapper.add(brand);
 
     /*提交事务*/
sqlSession.commit();

如果不想提交事务，可以在

SqlSession sqlSession=sqlSessionFactory.openSession();

openSession中填true即可自动添加

返回主键操作：

1	<insert id="add" useGeneratedKeys="true" keyProperty="id">

修改全部字段

接口修改：

1	int update(Brand brand);

sql语句：

<update id="update">
    update tb_brand
    set brandName=#{brandName},
        companyName=#{companyName},
        ordered=#{ordered},
        description=#{description},
        status=#{status}
    where id=#{id};
</update>

修改数据操作：

int status=1;
String companyName="博导";
String brandName="博导手机";
String description="手机中的战斗机";
int ordered=200;
int id =3;

/*封装对象*/
Brand brand=new Brand();
brand.setStatus(status);
brand.setCompanyName(companyName);
brand.setBrandName(brandName);
brand.setDescription(description);
brand.setOrdered(ordered);
brand.setId(id);

/*处理参数*/
companyName="%"+companyName+"%";
brandName="%"+brandName+"%";

String resource = "mybatis-config.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);

SqlSession sqlSession=sqlSessionFactory.openSession();

/*获取UserMapper的接口的代理对象*/
BrandMapper brandMapper=sqlSession.getMapper(BrandMapper.class);

int count=brandMapper.update(brand);
System.out.println(count);

sqlSession.commit();

/*4.释放资源*/
sqlSession.close();

删除

接口文件：

1	void deleteById(int id);

sql映射：

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

删除操作：

int id =3;
 
brandMapper.deleteById(id);

sqlSession.commit();

批量删除

接口文件

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

sql映射

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

批量删除操作

int[] ids={2,3,53};
String resource = "mybatis-config.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);

SqlSession sqlSession=sqlSessionFactory.openSession();

/*获取UserMapper的接口的代理对象*/
BrandMapper brandMapper=sqlSession.getMapper(BrandMapper.class);

brandMapper.deleteByIds(ids);

sqlSession.commit();
/*4.释放资源*/
sqlSession.close();

注解开发

使用注解开发会比配置文件开发更加方便

在接口中写：

1 2	@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

Mybatis持久层框架

长生风月

MyBatis

什么是MyBatis

MyBatis快速入门/Mapper代理开发

MyBatis核心配置文件设置

MyBatis之查询

多条件查询

选择性多条件查询

单条件查询

添加元素

修改全部字段

删除

批量删除

注解开发

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