mybatis复习-CFANZ编程社区

mybatis

使用mybatis
在项目中引入

<!-- https://mvnrepository.com/artifact/org.mybatis/mybatis -->
<dependency>
    <groupId>org.mybatis</groupId>
    <artifactId>mybatis</artifactId>
    <version>3.5.2</version>
</dependency>

持久层
Dao层、Service层、Controller层
完成持久化工作的代码块
层的界限十分明显

在项目中使用mybatis

创建数据库
在项目中引入依赖

<!-- 导入依赖 -->
<dependencies>
	<!-- mysql驱动 -->
	<dependency>
		<groupId>mysql</groupId>
		<artifactId>mysql-connector-java</artifactId>
		<version>5.1.47</version>
	</dependency>
	<!-- mybatis -->
	<!-- https://mvnrepository.com/artifact/org.mybatis/mybatis -->
	<dependency>
		<groupId>org.mybatis</groupId>
		<artifactId>mybatis</artifactId>
		<version>3.5.2</version>
	</dependency>
	<!-- junit -->
	<dependency>
		<groupId>junit</groupId>
		<artifactId>junit</artifactId>
		<version>4.12</version>
		<scope>test</scope>
	</dependency>
</dependencies>

在项目模块中创建mybatis-config核心配置文件

<?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核心配置文件 -->
<configuration>

    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/mybatis?useSSL=true&amp;useUnicode=true&amp;characterEncoding=UTF-8"/>
                <property name="username" value="root"/>
                <property name="password" value="root"/>
            </dataSource>
        </environment>
    </environments>

<!--    <mappers>-->
<!--        <mapper resource="org/mybatis/example/BlogMapper.xml"/>-->
<!--    </mappers>-->
</configuration>

编写mybatis工具类

//sqlSessionFactory --> sqlSession
public class MybatisUtils {

    //提升作用域
    private static SqlSessionFactory sqlSessionFactory;

    static {
        try {
            //使用Mybatis第一步：获取sqlSessionFactory对象
            String resource = "org/mybatis/example/mybatis-config.xml";
            InputStream inputStream = Resources.getResourceAsStream(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    //既然有了 SqlSessionFactory，顾名思义，我们可以从中获得 SqlSession 的实例。
    //sqlSession 完全包含了面向数据库执行SQL 命令所需的所有方法

    public static SqlSession getSqlSession(){
        return sqlSessionFactory.openSession();
    }

}

根据数据库字段创建pojo实体类
创建接口//Dao接口 public interface UserDao { List<User> getUserList(); }
创建接口实现类（用mapper代替接口Impl）

<?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=绑定一个对应的Dao/Mapper接口 -->
<mapper namespace="com.fj.dao.UserDao">
    <!-- select查询语句 -->
    <select id="getUserList" resultType="com.fj.pojo.User">
        select * from mybatis.user;
    </select>
</mapper>

CRUD

@Test
public void getUserByID(){
	SqlSession sqlSession = MybatisUtils.getSqlSession();

	UserMapper mapper = sqlSession.getMapper(UserMapper.class);
	User user = mapper.getUserByID(1);
	System.out.println(user);

	sqlSession.close();
}

//增删改需要提交事务
@Test
public void addUser(){
	SqlSession sqlSession = MybatisUtils.getSqlSession();

	UserMapper mapper = sqlSession.getMapper(UserMapper.class);
	User user = new User(4, "王五", "1324214");
	int result = mapper.addUser(user);
	if (result > 0){
		System.out.println("插入成功！");
	}

	//提交事务
	sqlSession.commit();

	sqlSession.close();
}

@Test
public void updateUser(){
	SqlSession sqlSession = MybatisUtils.getSqlSession();

	UserMapper mapper = sqlSession.getMapper(UserMapper.class);
	User user = new User(4, "旺财", "14432434");
	mapper.updateUser(user);

	sqlSession.commit();

	sqlSession.close();
}

@Test
public void deleteUser(){
	SqlSession sqlSession = MybatisUtils.getSqlSession();

	UserMapper mapper = sqlSession.getMapper(UserMapper.class);
	mapper.deleteUser(4);

	sqlSession.commit();

	sqlSession.close();
}

rud需要提交事务

使用注解开发

在接口中使用注解，然后在mapper中用mapper绑定接口，进行测试、
在这里插入图片描述
面试题：#{} ${}的区别

多对一处理

关联：多对一处理，association

按照查询嵌套处理
1、先查询多对象（学生类）的属性，复杂属性通过结果集映射查询

<!--
		javaType：把SQL语句查询出来的结果集，封装给某个类的对象（可省略）
		select：下一条要执行的SQL语句
		property：注入给实体类的某个属性
		上一次的查询结果集中，用哪些值作为条件去执行下一条SQL语句
	-->
	<association property="teacher" column="tid" 
	javaType="Teacher" select="getTeacher"/>

@Data
public class Student {
    private int id;
    private String name;

    //**学生需要关联一个老师**
    private Teacher teacher;
}

按照查询嵌套处理

<!-- 按照结果嵌套查询 -->
<select id="getStudent2" resultMap="StudentTeacher2">
	select s.id sid, s.name sname, t.name tname
	from student s, teacher t
	where s.tid = t.id
</select>
    
<resultMap id="StudentTeacher2" type="Student">
	<result property="id" column="sid"/>
	<result property="name" column="sname"/>
	<association property="teacher" javaType="Teacher">
		<result property="name" column="tname"/>
	</association>
</resultMap>

javaType直接用结果，然后再association里面添加result<result property="name" column="tname"/>

一对多

集合：老师的属性里面是学生

@Data
public class Teacher {
    private int id;
    private String name;

    //一个老师拥有多个学生
    private List<Student> students;

}

总结：javaType用来指定实体类中属性的类型
ofType用来指定映射到List或者集合中的pojo类型，泛型中的约束条件

后面缓存、动态sql