Mybatis的入门第一步

1.Mybatis的入门 1.添加依赖

            mysql
            mysql-connector-java
            8.0.18
        
        
            junit
            junit
            4.12
        
        
        
            org.mybatis
            mybatis
            3.4.6
        

    
        src/main/resources
       
                    ***.xml
                
        false
    
    
        src/main/java
        
            ***.xml
        
        false
    

2.在resouces文件下新建xml文件db.properties

写配置文件

driver=com.mysql.cj.jdbc.Driver
url=jdbc:mysql://localhost:3306/mybatis?serverTimezone=Asia/Shanghai&useSSL=true&useUnicode=true&characterEncoding=utf-8
username=root
password=DRsXT5ZJ6Oi55LPQ

3.在resouces文件下新建xml文件mybatis-config-xml

4.创建一个MybatisUtils工具类

public class MybatisUtils {
    private static SqlSessionFactory sqlSessionFactory;
    static {
        String resource = "org/mybatis/example/mybatis-config.xml";
        InputStream inputStream = null;
        try {
            inputStream = Resources.getResourceAsStream(resource);
        } catch (IOException e) {
            e.printStackTrace();
        }
        sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
    }
    public SqlSession getSqlSession() {
        return sqlSessionFactory.openSession();
    }
}

5.创建xml文件XxxMapper.xml映射dao层接口

    
        select * from user
    

6.添加日志

5.测试

@Test
    public void test() {
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserDao userDao = sqlSession.getMapper(UserDao.class);
        List userList = userDao.getUserList();
        for (User user : userList) {
            System.out.println(user);
        }
        sqlSession.close();
    }

2.增删改查 1.select

        select * from user where id = #{id}
    
 
2.delete 

        delete
        from USER
        where id = #{id};
    
 
3.update 

        update USER
        set name = #{name},pwd = #{pwd}
        where id = #{id};
    
 
4.insert 

        insert into USER (id,name ,pwd)
        values (#{id},#{name},#{pwd});
    
 
5.模糊查询 

        select * from user where name like concat('%',#{name},'%')
    
    

6.分页查询

    
        select * from user limit #{startIndex},#{pageSize}
    
 
3.起别名 
3.1具体的某个文件 

  
  
  
  
  
  

 
3.2给包名起别名 

  

 
注，用别名的时候直接用文件名，全小写
 
3.3用注解起别名 
@Alias("author")
 
注，直接在类上注解
 
4.解决实体属性名与数据库列名不一致问题 
1.建一个resultMap标签 

    //property实体类里的，column数据库里的
  
  
  

 
2.引用 
然后在引用它的语句中设置 resultMap 属性就行了（注意我们去掉了 resultType 属性）。比如:
 

  select user_id, user_name, hashed_password
  from some_table
  where id = #{id}

5.使用注解 5.1在接口上写注解

public interface UserMapper {

//    使用注解
    @Select("select * from user")
    List getUserListAnnotate();
}

5.2进行绑定

6.association和collection

association用于对象，关联

collection用于集合

6.1一对多

实体类

@Data
@AllArgsConstructor
@NoArgsConstructor
public class Student {
    private int id;
    private String name;
    private Teacher teacher;
}

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

第一种查询

    select * from student


    


    select * from teacher where id = #{tid}

  
第二种查询
 

    select s.id sid,s.name sname,t.id tid,t.name tname
    from student s,teacher t
    where s.tid = t.id


    
    
    
        
        
    

6.2多对一

实体类

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

@Data
@AllArgsConstructor
@NoArgsConstructor
public class Teacher {
    private int id;
    private String name;
    private List student;
}

第一种查询

    
        select t.id id,t.name tname,s.id sid,s.name sname,s.tid tid
        from teacher t,student s
        where t.id=s.tid
    
    
        
        
        
            
            
        
    
  
第二种查询
 

    
        select * from teacher where id = #{id}
    
    
        
    
    
        select * from student where tid = #{id}
    
  
7.动态查询 
7.1模糊查询if标签 
接口 
//查询
List getBlogIf(Map map);
 
if 

    select * from blog
    
        
            and title like concat('%',#{title},'%')
        
        
            and author like concat('%',#{author}.'%')
        
    

7.2更新数据set标签

接口

set标签

    update blog
    
        
            title = #{title},
        
        
            author = #{author},
        
        
            views = #{views},
        
    
    where id = #{id}

7.3Forech

forech

    select * from blog
    
        
            id = #{id}
        
    

测试

@Test
public void queryForech() {
    SqlSession sqlSession = MybatisUtils.getSqlSession();
    BlogMapper mapper = sqlSession.getMapper(BlogMapper.class);
    ArrayList arrayList = new ArrayList();
    arrayList.add(1);
    arrayList.add(2);
    HashMap hashMap = new HashMap();
    hashMap.put("ids",arrayList);
    mapper.queryForeach(hashMap);

    sqlSession.close();
}

8.二级缓存 8.1在mybatis-config.xml中开启全局缓存

8.1添加局部缓存，在xxMapper.xml中添加