MyBatis的CRUD

分手后的思念是犯贱 2022-02-24 06:44 367阅读 0赞

## MyBatis的认识 ##

1.MyBatis 是一个支持普通SQL查询，存储过程( Oracle最后一天)和高级映射的优秀持久层框架。  
2.MyBatis 消除了几乎所有的JDBC代码和手工设置参数以及结果集的检索。  
3.MyBatis 使用简单的 XML或注解用于配置和原始映射，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。  
4.MyBatis不能自动创建表，如果能够自动建表，必须自己先准备好建表的sql语句。

## MyBatis的简单查询 ##

1.先创建一个简单的java项目  
2.导包  
① 先创建一个文件夹lib存放jar包  
② 导入需要的jar包  
![在这里插入图片描述][2019040312242986.png]  
3.因为MyBatis不会自动建表，所以需要现在数据库中创建数据表(employee表为例)  
4.配置MyBatis的核心配置文件，文件名随意  
mybatis.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>
    	
        <properties resource="jdbc.properties"/>
        
        <environments default="development">
    	
            <environment id="development">
            
                <transactionManager type="JDBC"/>
                
                <dataSource type="POOLED">
                    <property name="driver" value="${jdbc.driver}"/>
                    <property name="url" value="${jdbc.url}"/>
                    <property name="username" value="${jdbc.username}"/>
                    <property name="password" value="${jdbc.password}"/>
                </dataSource>
            </environment>
        </environments>
        <mappers>
       	    
            <mapper resource="my/domain/EmployeeMapper.xml"/>
        </mappers>
    </configuration>

5.配置映射文件，命名格式：XxxxMapper.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="my.domain.EmployeeMapper">
        
        <!-- 
    		select : 这里面写查询语句
    		id:用来确定这条sql语句的唯一
    			   以后我们确定唯一,也就是找sql语句 : namespace +.+ id
    			 例: cn.itsource.mybatis.day1._1_hello.ProductMapper.get
    		parameterType : 传入的参数类型  long:大Long  _long:小long (具体的对应请参见文档)
    		resultType : 结果类型(第
            <select id="findOne" parameterType="long" resultType="my.domain.Employee">
        	
              select * from employee where id=#{id}
        
            </select>
        
            <select id="findAll" resultType="my.domain.Employee">
        
              select * from employee
        
            </select>

6.java代码

@Test
        public void testName() throws IOException {
        	//读取MyBatis核心配置文件
            Reader reader = Resources.getResourceAsReader("mybatis.xml");
            //创建SqlSessionFactory对象
            SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(reader);
            //创建SqlSession对象
            SqlSession session = factory.openSession();
            //查询单条数据
           /* Employee employee = session.selectOne("my.domain.EmployeeMapper.findOne",1l);
            System.out.println(employee);*/
    
    		//查询多条数据
            List<Employee> employees = session.selectList("my.domain.EmployeeMapper.findAll");
            for (Employee employee:employees){
                System.out.println(employee);
            }
            //关闭会话
            session.close();
        }

7.抽取工具类SessionUtils

public class SessionUtils {
        private static SqlSessionFactory factory;
        static{
            try{
                Reader reader = Resources.getResourceAsReader("mybatis.xml");
                factory = new SqlSessionFactoryBuilder().build(reader);
            }catch (Exception e){
                e.printStackTrace();
            }
        }
        public static SqlSession getSession(){
            return factory.openSession();
        }
    }

## MyBatis的CRUD ##

###### 注意：增删改需要提交事务 ######

1.添加数据  
①java代码

@Test
        public void save(Employee employee){
            SqlSession session=null;
            try {
                session = SessionUtils.getSession();
                session.insert("my.domain.EmployeeMapper.save", employee);
                Long id = employee.getId();//获取添加后对象在数据库的主键值
                session.commit();
            }catch (Exception e){
                e.printStackTrace();
            }finally {
                session.close();
            }
        }

② 配置映射文件

<insert id="save" parameterType="my.domain.Employee"
                useGeneratedKeys="true"   是否需要主键
                keyProperty="id">  对象中主键的属性
            insert into employee(username,password,email,headImage,age,
            department_id) values (#{username},#{password},#{email},#{headImage},#{age}
            ,#{department_id})
    </insert>

2.修改数据  
① java代码

@Test
        public void update(Employee employee){
            SqlSession session=null;
            try {
                session = SessionUtils.getSession();
                session.update("my.domain.EmployeeMapper.update",employee);
                session.commit();
            }catch (Exception e){
                e.printStackTrace();
            }finally {
                session.close();
            }
        }

② 配置映射文件

<update id="update" parameterType="my.domain.Employee">
          update employee set username=#{username},password=#{password},email=#{email},
          headImage=#{headImage},age=#{age},department_id=#{department_id} where id=#{id}
        </update>

3.删除数据  
① java代码

@Test
        public void delete(Long id){
            SqlSession session=null;
            try {
                session = SessionUtils.getSession();
                session.delete("my.domain.EmployeeMapper.delete",id);
                session.commit();
            }catch (Exception e){
                e.printStackTrace();
            }finally {
                session.close();
            }
        }

② 配置映射文件

<delete id="delete" parameterType="long" >
           delete from employee where id=#{id}
        </delete>

4.查询数据  
① java代码

@Test
        public void findAll() throws IOException {
            SqlSession session = SessionUtils.getSession();
            List<Employee> employees = session.selectList("my.domain.EmployeeMapper.findAll");
            for (Employee employee:employees){
                System.out.println(employee);
            }
            session.close();
        }
        @Test
        public void findOne() throws IOException {
            SqlSession session = SessionUtils.getSession();
            Employee employee = session.selectOne("my.domain.EmployeeMapper.findOne",1);
            System.out.println(employee);
            session.close();
        }

② 配置映射文件

<select id="findOne" parameterType="long" resultType="my.domain.Employee">
          select * from employee where id=#{id}
        </select>
    
        <select id="findAll" resultType="Employee" >
          select * from employee
        </select>

## MyBatis中为一个类取别名 ##

方式一：内置别名  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0p1bmVfRmx5aW5nRnJvc3Q_size_16_color_FFFFFF_t_70]  
方式二：自定义别名  
在MyBaeis的核心配置文件中配置一下代码，在映射文件中的parameterType ，resultType上可以直接写对象的类名

<typeAliases>
    		
    <typeAlias alias="employee" type="my.domain.Employee" />
    
    <package name="my.domain" />
    </typeAliases>

## 解决类名和属性名不对应问题 ##

1.在映射文件上配置

<resultMap type="cn.itsource.domain.Product" id="productMap">
    	
    	<id column="id" property="id"  />
    	<result column="productName" property="name" />
    </resultMap>
    
    <select id="queryOne" parameterType="long" resultMap="productMap">
    	select * from product where id = #{id}
    </select>

[2019040312242986.png]: /images/20220224/73e6acf5f73d4cf5b8314f1ebd739d2f.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0p1bmVfRmx5aW5nRnJvc3Q_size_16_color_FFFFFF_t_70]: /images/20220224/f4598f6edebb468bb3e67f0f333af33e.png