Mybatis详解--实战上手看这篇就够了

比眉伴天荒 2022-12-26 13:29 230阅读 0赞

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<table> 
 <tbody> 
  <tr> 
   <td><font>Mybatis简介</font></td> 
  </tr> 
 </tbody> 
</table>

## 简介 ##

MyBatis 是支持定制化 SQL、存储过程以及高级映射的优秀的持久层框架。MyBatis 避免了几乎所有的 JDBC 代码和手动设置参数以及获取结果集。MyBatis 可以对配置和原生Map使用简单的 XML 或注解，将接口和 Java 的 POJOs(Plain Old Java Objects,普通的 Java对象)映射成数据库中的记录。  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JlaXhpc2h1bw_size_16_color_FFFFFF_t_70]

本文讲使用Idea集成开发环境利用Maven构建Mybatis项目，Idea可以下载Mybatis plugin，然后可更好的使用mybatis。

**Mybatis整体架构：**  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JlaXhpc2h1bw_size_16_color_FFFFFF_t_70 1]

<table> 
 <tbody> 
  <tr> 
   <td><font>Mybatis入门</font></td> 
  </tr> 
 </tbody> 
</table>

## Mybatis环境搭建及Demo ##

1.使用IDEA创建maven工程  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JlaXhpc2h1bw_size_16_color_FFFFFF_t_70 2]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JlaXhpc2h1bw_size_16_color_FFFFFF_t_70 3]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JlaXhpc2h1bw_size_16_color_FFFFFF_t_70 4]  
2.在pom.xml添加依赖  
  添加依赖包：mybatis包、数据库驱动包(我使用的是mysql)、日志包(我使用的是log4j)

<dependencies>
          
        <dependency>
          <groupId>junit</groupId>
          <artifactId>junit</artifactId>
          <version>4.11</version>
          <scope>test</scope>
        </dependency>
        
        
        <dependency>
            <groupId>log4j</groupId>
          <artifactId>log4j</artifactId>
            <version>1.2.16</version>
        </dependency>
        
        
        <dependency>
            <groupId>org.mybatis</groupId>
          <artifactId>mybatis</artifactId>
            <version>3.2.6</version>
        </dependency>
        
        
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.12</version>
        </dependency>
        
      </dependencies>

3.准备数据  
![在这里插入图片描述][20201205221000570.png]  
4.User实体类

public class User {
        
        int id;
        String name;
        String password;
        /*省略get/set*/
        }

5.与实体类相对应的实体类映射文件(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="MyMapper">
        
        <select id="selectUser" parameterType="int" resultType="com.beixi.entity.User">
          select * from user where id = #{
        id}
       </select>
    </mapper>

6.全局配置文件（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="test">
            
            <environment id="test">
                
                <transactionManager type="JDBC" />
                
                <dataSource type="POOLED">
                    <property name="driver" value="com.mysql.jdbc.Driver" />
                    <property name="url" value="jdbc:mysql://127.0.0.1:3306/test?characterEncoding=UTF-8" />
                    <property name="username" value="root" />
                    <property name="password" value="root" />
                </dataSource>
            </environment>
        </environments>
        <mappers>
            <mapper resource="mappers/UserMapper.xml" />
        </mappers>
    </configuration>

7.测试类

public class UserTest {
        
        public static void main(String[] args) throws Exception {
        
            // 指定全局配置文件
            String resource = "mybatis-config.xml";
            // 读取配置文件
            InputStream inputStream = Resources.getResourceAsStream(resource);
            // 构建sqlSessionFactory
            SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
            // 获取sqlSession
            SqlSession sqlSession = sqlSessionFactory.openSession();
            try {
        
                // 操作CRUD，第一个参数：指定statement，规则：命名空间+“.”+statementId
                // 第二个参数：指定传入sql的参数：这里是用户id
                User user = sqlSession.selectOne("MyMapper.selectUser", 1);
                System.out.println(user);
            } finally {
        
                sqlSession.close();
            }
        }
    }

8.目录结构  
![在这里插入图片描述][20201205223045582.png]  
9.添加日志分析log4j.properties

log4j.rootLogger=DEBUG,A1
    log4j.logger.org.apache=DEBUG
    log4j.appender.A1=org.apache.log4j.ConsoleAppender
    log4j.appender.A1.layout=org.apache.log4j.PatternLayout
    log4j.appender.A1.layout.ConversionPattern=%-d{
        yyyy-MM-dd HH:mm:ss,SSS} [%t] [%c]-[%p] %m%n

再次运行程序会打印日志：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JlaXhpc2h1bw_size_16_color_FFFFFF_t_70 5]

<table> 
 <tbody> 
  <tr> 
   <td><font>完整的CRUD操作</font></td> 
  </tr> 
 </tbody> 
</table>

## 完整的CRUD操作 ##

1.创建UserDao持久层

public class UserDao {
        
        /*持久化对象*/
        public SqlSession sqlSession;
    
        public UserDao(SqlSession sqlSession) {
        
            this.sqlSession = sqlSession;
        }
        /*根据id查询用户信息*/
        public User queryUserById(String id) {
        
            return this.sqlSession.selectOne("UserDao.queryUserById", id);
        }
        /*查询所有用户信息*/
        public List<User> queryUserAll() {
        
            return this.sqlSession.selectList("UserDao.queryUserAll");
        }
        /*新增*/
        public void insertUser(User user) {
        
            this.sqlSession.insert("UserDao.insertUser", user);
        }
        /*更新*/
        public void updateUser(User user) {
        
            this.sqlSession.update("UserDao.updateUser", user);
        }
        /*删除*/
        public void deleteUser(int id) {
        
            this.sqlSession.delete("UserDao.deleteUser", id);
        }
    }

2.修改UserMapper.xml

<mapper namespace="UserDao">
        
        
        
        
    
        
        <select id="queryUserById" parameterType="int" resultType="com.beixi.entity.User">
          select * from user  where id = #{
        id};
       </select>
    
        <select id="queryUserAll" resultType="com.beixi.entity.User">
            select * from user;
        </select>
    
        
        <insert id="insertUser" parameterType="com.beixi.entity.User">
            INSERT INTO user (
            name,
            password
            )
            VALUES
            (
            #{
        name},
            #{
        password}
            );
        </insert>
    
        <update id="updateUser" parameterType="com.beixi.entity.User">
            UPDATE user
            <trim prefix="set" suffixOverrides=",">
                <if test="name!=null">name = #{
        name},</if>
                <if test="password!=null">password = #{
        password},</if>
            </trim>
            WHERE
            (id = #{
        id});
        </update>
    
        <delete id="deleteUser">
            delete from user where id=#{
        id}
        </delete>
    </mapper>

3.编写UserDao的测试用例

public class UserDaoTest {
        
        public UserDao userDao;
        public SqlSession sqlSession;
    
        @Before
        public void setUp() throws Exception {
        
            // mybatis-config.xml
            String resource = "mybatis-config.xml";
            // 读取配置文件
            InputStream is = Resources.getResourceAsStream(resource);
            // 构建SqlSessionFactory
            SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);
            // 获取sqlSession
            sqlSession = sqlSessionFactory.openSession();
            this.userDao = new UserDao(sqlSession);
        }
    
        @Test
        public void queryUserById() throws Exception {
        
            System.out.println(this.userDao.queryUserById(1));
        }
    
        @Test
        public void queryUserAll() throws Exception {
        
            List<User> userList = this.userDao.queryUserAll();
            for (User user : userList) {
        
                System.out.println(user);
            }
        }
    
        @Test
        public void insertUser() throws Exception {
        
            User user = new User();
            user.setName("贝西奇谈");
            user.setPassword("123456");
            this.userDao.insertUser(user);
            this.sqlSession.commit();//提交事务
        }
    
        @Test
        public void updateUser() throws Exception {
        
            User user = new User();
            user.setName("杰哥");
            user.setPassword("654321");
            user.setId(89);
            this.userDao.updateUser(user);
            this.sqlSession.commit();
        }
    
        @Test
        public void deleteUser() throws Exception {
        
            this.userDao.deleteUser(89);
            this.sqlSession.commit();
        }
    
    }

**模糊查询**

<select id="selectLike"  parameterType="string"  resultType="User">
    		select * from user where name like concat("%",#{
        name},"%")
    	</select>

/*模糊查询*/
    	@Test
    	public void selectLike(){
        
    		List<User> list = sqlSession.selectList("selectLike","zhang");
    		for (int i = 0; i < list.size(); i++) {
        
    			User user = list.get(i);
    			System.out.println(user);
    		}
    	}

<table> 
 <tbody> 
  <tr> 
   <td><font>解决数据库字段名和实体类属性名不一致的问题</font></td> 
  </tr> 
 </tbody> 
</table>

## 解决数据库字段名和实体类属性名不一致的问题 ##

原因：数据库的字段名是name，POJO中的属性名字是userName  
两端不一致，造成mybatis无法填充对应的字段信息。修改方法：resultMap。  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JlaXhpc2h1bw_size_16_color_FFFFFF_t_70 6]

<table> 
 <tbody> 
  <tr> 
   <td><font>typeAliases</font></td> 
  </tr> 
 </tbody> 
</table>

## typeAliases ##

类型别名是为 Java 类型命名的一个短的名字。它只和 XML 配置有关，存在的意义仅在于用来减少类完全限定名的冗余。

缺点：每个pojo类都要去配置。  
解决方案：使用扫描包，扫描指定包下的所有类，扫描之后的别名就是类名（不区分大小写），建议使用的时候和类名一致。

Mybatis已经为普通的 Java 类型内建了许多相应的类型别名。它们都是大小写不敏感的.  
![在这里插入图片描述][20201205231336992.png]

## 多对一的关联映射 ##

（1）数据  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JlaXhpc2h1bw_size_16_color_FFFFFF_t_70 7]  
（2）映射文件  
多方出发：

<resultMap type="Emp" id="empMap">
    	 <id  column="id" property="id"  />
    	 <result  column="ename"  property="name"/>
    	 <result  column="eage"  property="age"/>
    	 <result  column="esex"  property="sex"/>
    	 
    	 <association property="dept" column="deptno" javaType="Dept" >
    	  <id column="dno"  property="dno"/>
    	  <result  column="dname"  property="name"/>
    	 </association>
    	</resultMap>
    	<select id="selectEmpOne" parameterType="int" resultMap="empMap">
    		select * from emp e,dept d where e.deptno=d.dno and  e.id = #{
        id}
    	</select>
    	
    测试：
    /*查询单条*/
    	@Test
    	public void selectEmpOne(){
        
    		//第一个参数是调用的sql  第二个是传入的参数
    		Emp emp =(Emp) sqlSession.selectOne("selectEmpOne", 7);
    		System.out.println(emp);
    	}

一的一方出发：

<resultMap type="Dept" id="deptMap">
    		 <id column="dno"  property="dno"/>
    	  <result  column="dname"  property="name"/>
    	  
    	  <collection property="emps" column="deptno"  javaType="Emp">
    	   <id  column="id" property="id"  />
    		 <result  column="ename"  property="name"/>
    		 <result  column="eage"  property="age"/>
    		 <result  column="esex"  property="sex"/>
    	  </collection>
    	</resultMap>
    	
    <select id="selectEmpByDeptOne" parameterType="int" resultMap="deptMap">
    		select * from emp e,dept d where e.deptno=d.dno and  d.dno = #{
        dno}
    	</select>
    
    
    	@Test
    	public void selectEmpByDeptOne(){
        
    		//第一个参数是调用的sql  第二个是传入的参数
    		Dept dept =(Dept) sqlSession.selectOne("selectEmpByDeptOne", 10);
    		System.out.println(dept);
    		Set<Emp> emps = dept.getEmps();
    		for(Emp emp:emps){
        
    			System.out.println(emp);
    		}
    	}

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