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# MyBatis 数据库框架入门案例

# 创建数据库 mybatis 和表 users

create database mybatis;
use mybatis;
CREATE TABLE users(id INT PRIMARY KEY AUTO_INCREMENT, NAME VARCHAR(20), age INT);
INSERT INTO users(NAME, age) VALUES('孤傲苍狼', 19);
INSERT INTO users(NAME, age) VALUES('白虎神皇', 29);

# 添加 mybatis 框架 jar 包（核心包 + 驱动包 + 依赖包）

image-20210729144420878

# 创建数据库配置文件 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>
    <!--1. 配置环境 ，默认的环境 id 为 mysql-->
    <environments default="mysql">
            <!--1.2. 配置 id 为 mysql 的数据库环境 -->
             <environment id="mysql">
                <!-- 使用 JDBC 的事务管理 -->
                <transactionManager type="JDBC" />
                <!-- 数据库连接池 -->
                <dataSource type="POOLED">
			        <property name="driver"  value="com.mysql.jdbc.Driver" />
			        <property name="url"  value="jdbc:mysql://localhost:3306/mybatis" />
			        <property name="username" value="root" />
			        <property name="password" value="root" />
                </dataSource>
            </environment>
</environments>
   
</configuration>
# 定义数据库 user，对应的实体类 User
package me.gacl.domain;
  
  /**
   * @author gacl
   * users 表所对应的实体类
   */
  public class User {
  
      // 实体类的属性和表 User 的字段名称一一对应
     private int id;
     private String name;
     private int age;
 
     public int getId() {
         return id;
     }
 
     public void setId(int id) {
         this.id = id;
     }
 
     public String getName() {
         return name;
     }
 
     public void setName(String name) {
         this.name = name;
     }
 
     public int getAge() {
         return age;
     }
 
     public void setAge(int age) {
         this.age = age;
     }
 
     @Override
     public String toString() {
         return "User [id=" + id + ", name=" + name + ", age=" + age + "]";
     }
 }
# MyBatis 映射（新建一个包，专门用于存放 sql 映射文件）userMapper.xml
<?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="me.gacl.mapping.userMapper">
     <select id="getUser" parameterType="int"  resultType="me.gacl.domain.User">
             select * from users where id=#{id}
     </select>
</mapper>
# 在 mybatis-config.xml 文件中注册 userMapper.xml 文件
<!-- 注册 userMapper.xml 文件， userMapper.xml 位于 me.gacl.mapping 这个包下，所以 resource 写成 me/gacl/mapping/userMapper.xml -->
	<mappers>
		<mapper resource="me/gacl/mapping/userMapper.xml" />
	</mappers>
# 编写 Test1 测试类
package me.gacl.test;
import java.io.IOException;
import java.io.InputStream;
import java.io.Reader;
import me.gacl.domain.User;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
public class Test1 {
public static void main(String[] args) throws IOException {
        //mybatis 的配置文件
         String resource = "mybatis-config.xml";
        // 加载关联的映射文件
         InputStream is =Resources.getResourceAsStream(resource);
        // 构建 sqlSession 的工厂
         SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(is);
        // 创建能执行映射文件中 sql 的 sqlSession
        SqlSession session = sessionFactory.openSession();
        /**
         * 映射 sql 的标识字符串，
         * me.gacl.mapping.userMapper 是 userMapper.xml 文件中 mapper 标签的 namespace 属性的值，
         * getUser 是 select 标签的 id 属性值，通过 select 标签的 id 属性值就可以找到要执行的 SQL
         */
         String statement = "me.gacl.mapping.userMapper.getUser";// 映射 sql 的标识字符串
        // 执行查询返回一个唯一 user 对象的 sql
        User user = session.selectOne(statement, 1);
        System.out.println(user);
    }
}
# 运行结果（查询 id=1 的信息）
image-20210729145533605
# 创建数据表，并实现增删改查
# 数据库 mybatis student
create database mybatis character set utf8;
use mybatis;
CREATE TABLE student(
id INT PRIMARY KEY AUTO_INCREMENT, 
name VARCHAR(20), 
grade int,
department VARCHAR(20)
);
INSERT INTO student (name, grade,department) VALUES('孤傲苍狼', 2020, '抓鱼专业');
INSERT INTO student (name, grade,department) VALUES('王者', 2021, '游戏boss专业');
INSERT INTO student (name, grade,department) VALUES('孤傲苍狼2', 2022, '扫地专业');
INSERT INTO student (name, grade,department) VALUES('孤傲苍狼3', 2021, '航天狩猎专业');
INSERT INTO student (name, grade,department) VALUES('孤傲苍狼4', 2020, '抓鱼专业');

# Student 实体类 (get and set + to string)
package me.gacl.domain;
public class Student {
	private Integer id;
	private String name;
	private Integer grade;
	private String department;
	public Integer getId() {
		return id;
	}
	public void setId(Integer id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public Integer getGrade() {
		return grade;
	}
	public void setGrade(Integer grade) {
		this.grade = grade;
	}
	public String getDepartment() {
		return department;
	}
	public void setDepartment(String department) {
		this.department = department;
	}
	@Override
	public String toString() {
		return "Student [id=" + id + ", name=" + name + ", grade=" + grade + ", department=" + department + "]";
	}
}
# studentMapper.xml 映射文件
<?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="me.gacl.mapping.studentMapper">
	<insert id="insertOneStudent"
		parameterType="me.gacl.domain.Student">
		insert into student
		(name,grade,department)values(#{name},#{grade},#{department} );
	</insert>
	<select id="getStudent" parameterType="int"
		resultType="me.gacl.domain.Student">
		select * from student where id=#{id}
	</select>
	<update id="updateStudent"
		parameterType="me.gacl.domain.Student">
		update student
		set department = "计算机" where name
		=#{name};
	</update>
	<delete id="deleteStudent" parameterType="String">
		delete from
		student
		where name=#{name};
	</delete>
</mapper>
# 在 mybatis-config.xml 中注册 studentMapper.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>
	<!--1.配置环境 ，默认的环境id为mysql -->
	<environments default="mysql">
		<!--1.2.配置id为mysql的数据库环境 -->
		<environment id="mysql">
			<!-- 使用JDBC的事务管理 -->
			<transactionManager type="JDBC" />
			<!--数据库连接池 -->
			<dataSource type="POOLED">
				<property name="driver" value="com.mysql.jdbc.Driver" />
				<property name="url"
					value="jdbc:mysql://localhost:3306/mybatis" />
				<property name="username" value="root" />
				<property name="password" value="root" />
			</dataSource>
		</environment>
	</environments>
	<!-- 注册userMapper.xml文件， userMapper.xml位于me.gacl.mapping这个包下，所以resource写成me/gacl/mapping/userMapper.xml -->
	<mappers>
		<mapper resource="me/gacl/mapping/userMapper.xml" />
		<mapper resource="me/gacl/mapping/studentMapper.xml" />
	</mappers>
</configuration>
# 创建 Test1 类，测试增删改查
package me.gacl.test;
import java.io.IOException;
import java.io.InputStream;
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 me.gacl.domain.Student;
public class Test1 {
	public static void main(String[] args) throws IOException {
		// Student s1 = new Student();
		//s1.setDepartment ("计算机应用技术");
		// s1.setGrade(2021);
		//s1.setName ("张三");
		//mybatis 的配置文件
		String resource = "mybatis-config.xml";
		// 加载关联的映射文件
		InputStream is = Resources.getResourceAsStream(resource);
		// 构建 sqlSession 的工厂
		SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(is);
		// 创建能执行映射文件中 sql 的 sqlSession
		SqlSession session = sessionFactory.openSession();
		String statement = "me.gacl.mapping.studentMapper.deleteStudent";
		// int rows = session.insert(statement, s1);
		int rows = session.delete(statement, "张三");
		System.out.println("成功删除了" + rows + "条");
		session.commit();
		session.close();
	}
}
配置 studentMapper.xml ，修改 statement ，调用方法
# 运行结果（updateStudent）
image-20210730134802540
image-20210730134847025
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