MyBatis完成CRUD 详细细节内容剖析

package com.rainbowsea.mybatis.utils;
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;
public class SqlSessionUtil {
    // 工具类的构造方法一般都是私有话化的
    // 工具类中所有的方法都是静态的，直接类名即可调用，不需要 new 对象
    // 为了防止new对象，构造方法私有化。
    private SqlSessionUtil() {
    }
    private static SqlSessionFactory sessionFactory = null;
    // 静态代码块，类加载时执行
    // SqlSessionUtil 工具类在进行第一次加载的时候，解析mybatis-config.xml 文件，创建SqlSessionFactory对象。
    static {
        // 获取到  SqlSessionFactoryBuilder 对象
        SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();
        // 获取到SqlSessionFactory 对象
        // SQlsessionFactory对象，一个SqlSessionFactory对应一个 environment, 一个environment通常是一个数据库
        try {
            sessionFactory = sqlSessionFactoryBuilder.build(Resources.getResourceAsStream("mybatis-config.xml"));
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }
    /**
     * 获取会话对象
     * @return SqlSession
     */
    public static SqlSession openSession() {
        // 获取到 SqlSession 对象
        SqlSession sqlSession = sessionFactory.openSession();
        return sqlSession;
    }
}

<?xml version="1.0" encoding="UTF-8"?>
<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/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.rainbowsea</groupId>
    <artifactId>mybatis-002-crud</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>jar</packaging>
    <properties>
        <maven.compiler.source>17</maven.compiler.source>
        <maven.compiler.target>17</maven.compiler.target>
    </properties>
    <dependencies>
<!--              mybatis依赖 -->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.10</version>
        </dependency>
<!--    mysql驱动器-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.30</version>
        </dependency>
<!--        引入 junit4 依赖-->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.13.2</version>
            <scope>test</scope>
        </dependency>
        <!--        引入 logback的依赖，这个日志框架实现了slf4j 规范-->
        <dependency>
            <groupId>ch.qos.logback</groupId>
            <artifactId>logback-classic</artifactId>
            <version>1.2.11</version>
        </dependency>
    </dependencies>
</project>

<?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>
    <!--    开启mybatis 对标准日志的实现-->
    <!--    如果导入的第三方框架的日志，没有下面这个 settings 也是可以的-->
    <!--    <settings>-->
    <!--        <setting name="logImpl" value="STDOUT_LOGGING"/>-->
    <!--    </settings>-->
    <environments default="development">
        <environment id="development">
            <!--            MANAGED 没有用第三框架管理的话，都是会被提交的，没有事务上的管理了。-->
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/mybatis"/>
                <property name="username" value="root"/>
                <property name="password" value="MySQL123"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <!--sql映射文件创建好之后，需要将该文件路径配置到这里-->
        <!--        执行XxxMapper.xml 文件的路径-->
        <!--        resource 属性自动会从类的根路径下开始查找资源-->
        <!--        <mapper resource="CarMapper.xml"/>-->
        <!--        <mapper resource="com/CarMapper2.xml"/>-->
        <!--        url属性: 从绝对路径当中加载资源。-->
        <!--        语法格式：file:///绝对路径-->
        <!--        <mapper url="file:///e:/CarMapper.xml"></mapper>-->
        <mapper resource="CarMapper.xml"></mapper>
    </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先随意写一个-->
<mapper namespace="rainbowsea">
</mapper>

<?xml version="1.0" encoding="UTF-8"?>
<configuration debug="false">
    <!-- 控制台输出 -->
    <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
        <encoder class="ch.qos.logback.classic.encoder.PatternLayoutEncoder">
            <!--格式化输出：%d表示日期，%thread表示线程名，%-5level：级别从左显示5个字符宽度%msg：日志消息，%n是换行符-->
            <pattern>%d{yyyy-MM-dd HH:mm:ss.SSS} [%thread] %-5level %logger{50} - %msg%n</pattern>
        </encoder>
    </appender>
    <!--mybatis log configure-->
    <logger name="com.apache.ibatis" level="TRACE"/>
    <logger name="java.sql.Connection" level="DEBUG"/>
    <logger name="java.sql.Statement" level="DEBUG"/>
    <logger name="java.sql.PreparedStatement" level="DEBUG"/>
    <!-- 日志输出级别,logback日志级别包括五个：TRACE < DEBUG < INFO < WARN < ERROR -->
    <root level="DEBUG">
        <appender-ref ref="STDOUT"/>
        <appender-ref ref="FILE"/>
    </root>
</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先随便写-->
<mapper namespace="car">
    <insert id="insertCar">
        insert into t_car(car_num,brand,guide_price,produce_time,car_type) values('103', '奔驰E300L', 50.3, '2022-01-01', '燃油车')
    </insert>
</mapper>

// JDBC中使用 ? 作为占位符。那么MyBatis中会使用什么作为占位符呢？
String sql = "insert into t_car(car_num,brand,guide_price,produce_time,car_type) values(?,?,?,?,?)";
// ......
// 给 ? 传值。那么MyBatis中应该怎么传值呢？
ps.setString(1,"103");
ps.setString(2,"奔驰E300L");
ps.setDouble(3,50.3);
ps.setString(4,"2022-01-01");
ps.setString(5,"燃油车");

<?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先随意写一个-->
<mapper namespace="rainbowsea">
<!--	insert语句，id是这个条SQL语句的唯一标识，这个id就代表了这条SQL语句 -->
	<insert id="insertCar">
		insert into t_car(id,car_num,brand,guide_price,produce_time,car_type)
		values (null,#{k1},#{k2},#{k3},#{k4},#{k5})
<!--  map.get("fdsd") 找，结果找不到 = null-->
	</insert>
</mapper>

map.put("k1","111");
map.put("k2","比亚迪汉");
map.put("k3",10.0);
map.put("k4","2020-11-11");
map.put("k5","电车");

// 执行sql语句
// insert方法的参数:
// 第一个参数:sqlId；从CarMapper.xml 文件中复制,的对于是insert SQL 语句的 id 信息
// 第二个参数: 封装数据的对象，这里为 Map 集合
int count = sqlSession.insert("insertCar", map);

insert into t_car(id,car_num,brand,guide_price,produce_time,car_type) values (null,#{fdsd},#{k2},#{k3},#{k4},#{k5})
注意：#{这里写什么？写map集合的key,如果key不存在，获取的是null}

package com.rainbowsea.mybatis.pojo;
public class Car {
    //数据表当中的字段应该和pojo类的属性一一对应
    // 建议使用包装类，这样可以防止 null 的问题：int = null; 不行，Int = null 可以
    private Long id;
    private String carNum;
    private String brand;
    private Double guiderPrice;
    private String produceTime;
    private String carType;
    public Car() {
    }
    public Car(Long id, String carNum, String brand, Double guiderPrice, String produceTime, String carType) {
        this.id = id;
        this.carNum = carNum;
        this.brand = brand;
        this.guiderPrice = guiderPrice;
        this.produceTime = produceTime;
        this.carType = carType;
    }
    @Override
    public String toString() {
        return "Car{" +
                "id=" + id +
                ", carNum='" + carNum + '\'' +
                ", brand='" + brand + '\'' +
                ", guiderPrice=" + guiderPrice +
                ", produceTime='" + produceTime + '\'' +
                ", carType='" + carType + '\'' +
                '}';
    }
    public Long getId() {
        return id;
    }
    public void setId(Long id) {
        this.id = id;
    }
    public String getCarNum() {
        return carNum;
    }
/*    public String getXyz() {
        return carNum;
    }*/
    public void setCarNum(String carNum) {
        this.carNum = carNum;
    }
    public String getBrand() {
        return brand;
    }
    public void setBrand(String brand) {
        this.brand = brand;
    }
    public Double getGuiderPrice() {
        return guiderPrice;
    }
    public void setGuiderPrice(Double guiderPrice) {
        this.guiderPrice = guiderPrice;
    }
    public String getProduceTime() {
        return produceTime;
    }
    public void setProduceTime(String produceTime) {
        this.produceTime = produceTime;
    }
    public String getCarType() {
        return carType;
    }
    public void setCarType(String carType) {
        this.carType = carType;
    }
}

 public void testInsertCarByPOJO() {
        SqlSession sqlSession = SqlSessionUtil.openSession();
        // 封装数据
        Car car = new Car(null, "333", "比亚迪泰", 30.0, "2020-11-11", "新能源");
        // 执行SQL
        int count = sqlSession.insert("insertCar", car); // ORM       // 对应XxxMapper.xml 上的id
        System.out.println(count);
        sqlSession.commit();
        sqlSession.close();
    }

@Test
    public void testDeleteById() {
        SqlSession sqlSession = SqlSessionUtil.openSession();
        // 执行SQL语句
        sqlSession.delete("deleteById",44); // 如果只要一个值的时候，就不需要对应上的的 Object 类型了
        sqlSession.commit(); // 提交
        sqlSession.close(); // 关闭
    }

<update id="updateById">
		update t_car set car_num = #{carNum}, brand=#{brand}, guide_price=#{guiderPrice},produce_time=#{produceTime},
		                 car_type=#{carType} where id =#{id}
	</update>

   public void testUpdateById() {
        SqlSession sqlSession = SqlSessionUtil.openSession();
        Car car = new Car(46L, "999", "凯美瑞", 30.3, "1999-11-10", "燃油车");
        // 执行SQL语句
        int count = sqlSession.update("updateById", car);
        System.out.println(count);
        sqlSession.commit();
        sqlSession.close();
    }

<select id="selectById" resultType="com.rainbowsea.mybatis.pojo.Car">
		select id,car_num as carNum, brand, guide_price as guiderPrice,
		produce_time as produceTime,
		car_type as carType
		from t_car
		where id= #{id}
	</select>

<select id="selectById" resultType="com.rainbowsea.mybatis.pojo.Car">
		select id,car_num as carNum, brand, guide_price as guiderPrice,
		produce_time as produceTime,
		car_type as carType
		from t_car
		where id= #{id}
	</select>

<select id="selectAll" resultType="com.rainbowsea.mybatis.pojo.Car">
		select
		       id,car_num as carNum, brand, guide_price as guiderPrice,
			   produce_time as produceTime,
			   car_type as carType
		from
		       t_car
	</select>

   <select id="selectAll" resultType="com.rainbowsea.mybatis.pojo.Car">
      select
             id,car_num as carNum, brand, guide_price as guiderPrice,
            produce_time as produceTime,
            car_type as carType
      from
             t_car
   </select>
  List<Car> cars = sqlSession.selectList("selectAll");
注意: resultType 还是指定封装的结果集的类型，不是指定List类型，是指定List集合中元素的类型
selectList 方法，mybatis通过这个方法就可以得知你需要一个List集合，它会自动给你返回一个List集合

<?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先随意写一个-->
<mapper namespace="rainbowsea">
	<select id="selectAll" resultType="com.rainbowsea.mybatis.pojo.Car">
		select
			id,car_num as carNum, brand, guide_price as guiderPrice,
			produce_time as produceTime,
			car_type as carType
		from
			t_car
	</select>
</mapper>

<?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>
    <!--    开启mybatis 对标准日志的实现-->
    <!--    如果导入的第三方框架的日志，没有下面这个 settings 也是可以的-->
    <!--    <settings>-->
    <!--        <setting name="logImpl" value="STDOUT_LOGGING"/>-->
    <!--    </settings>-->
    <environments default="development">
        <environment id="development">
            <!--            MANAGED 没有用第三框架管理的话，都是会被提交的，没有事务上的管理了。-->
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/mybatis"/>
                <property name="username" value="root"/>
                <property name="password" value="MySQL123"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <!--sql映射文件创建好之后，需要将该文件路径配置到这里-->
        <!--        执行XxxMapper.xml 文件的路径-->
        <!--        resource 属性自动会从类的根路径下开始查找资源-->
        <!--        <mapper resource="CarMapper.xml"/>-->
        <!--        <mapper resource="com/CarMapper2.xml"/>-->
        <!--        url属性: 从绝对路径当中加载资源。-->
        <!--        语法格式：file:///绝对路径-->
        <!--        <mapper url="file:///e:/CarMapper.xml"></mapper>-->
        <mapper resource="CarMapper.xml"></mapper>
        <mapper resource="UserMapper.xml"></mapper>
    </mappers>
</configuration>

 public void testNamespace() {
        SqlSession sqlSession = SqlSessionUtil.openSession();
        // 执行SQL语句
        // 正确的完整写法:namespace.id
        List<Car> cars = sqlSession.selectList("selectAll");
        // 遍历
        cars.forEach(car -> {
            System.out.println(car);
        });
        //sqlSession.commit();  查询不用提交,没有事务问题
        sqlSession.close();
    }

@Test
    public void testNamespace() {
        SqlSession sqlSession = SqlSessionUtil.openSession();
        // 执行SQL语句
        // 正确的完整写法:namespace.id
        List<Car> cars = sqlSession.selectList("rainbowsea2.selectAll");
        // 遍历
        cars.forEach(car -> {
            System.out.println(car);
        });
        //sqlSession.commit();  查询不用提交,没有事务问题
        sqlSession.close();
    }