Mybatis笔记

小鱼儿 2022-04-10 04:09 163阅读 0赞

**JDBC不要用的地方?**

1.  处理结果集麻烦
2.  sql语句全部写在类里面,动态sql语句处理也麻烦
3.  连接池(数据源)放在tomcat里面
4.  不管怎么处理dao层里面总是存在大量的重复代码
5.  …

**mybatis开发步骤:**

1.  导包
2.  编写mybatis主配置文件(放在src目录下)
3.  编写单利的工具类用于获取数据库连接

public class MybatisUtil {
    	private static MybatisUtil mu=new MybatisUtil();
    	private SqlSessionFactory sf;
    	private MybatisUtil() {
    		InputStream is=MybatisUtil.class.getClassLoader().getResourceAsStream("mybatis.xml");
    		sf=new SqlSessionFactoryBuilder().build(is);
    	}
    	public static MybatisUtil init() {
    		return mu;
    	}
    	public SqlSession getSession() {
    		return sf.openSession();
    	}
    }

1.  编写mapper映射文件(放在和dao层接口一致的位置)
2.  在dao层中操作数据库  
    **具体调用在service的实现类中**

public class BookServiceImpl implements BookService {
    
    	@Override
    	public Book queryBookById(Integer id) {
    		SqlSession ss = MybatisUtil.init().getSession();
    		BookDao bd = ss.getMapper(BookDao.class);
    		Book book = bd.queryBookById(id);
    		ss.close();
    		return book;
    	}

**mybatis优化的部分:**

1.  设置允许mybatis插入null:  
    ![在这里插入图片描述][20181224191153713.png]
2.  提供动态sql语句
3.  提供log4j.properties配置文件(放在src下面)
4.  提供jdbc.propertis配置文件(放在src下面)
5.  给实体类全路径取别名

**一级二级缓存:redis**  
一级缓存:mybatis默认会给每个sqlsession默认提供一个一级缓存空间,当我们第一次使用该sqlsession执行查询的时候,mybatis会把查询结果放置在一级缓存中,第二次使用该sqlsession执行相同的sql语句的时候现从一级缓存中取,如果期间该sqlsession提交那么一级缓存中的数据清空  
二级缓存:mybatis会给每个命名空间提供二级缓存空间,多个sqlsession操作相同命名空间里面的相同sql语句二级缓存空间是共享的

**二级缓存步骤：**

1.  在主配置文件中允许二级缓存

1.  在需要二级缓存的命名空间中允许二级缓存

1.  第一个sqlsession执行完查询以后必须提交(只查询的话调用close方法也可以)才会把数据放到二级缓存中
2.  对实体类进行序列化

**mybatis.xml——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>
    	
    	<properties resource="jdbc.properties"></properties>
    	
    	<settings>
    		
    		<setting name="jdbcTypeForNull" value="NULL"/>
    	</settings>
    	
    	<typeAliases>
    		<typeAlias type="com.zl.pojo.FenYe" alias="fy"/>
    		<typeAlias type="com.zl.pojo.Car" alias="car"/>
    		<typeAlias type="com.zl.pojo.Query" alias="query"/>
    		<typeAlias type="com.zl.pojo.User" alias="user"/>
    		<typeAlias type="com.zl.pojo.Brand" alias="brand"/>
    		<typeAlias type="com.zl.pojo.Power" alias="power"/>
    		<typeAlias type="com.zl.pojo.Role" alias="role"/>
    	</typeAliases>
    	
    	<environments default="development">
    		<environment id="development">
    			
    			<transactionManager type="JDBC"></transactionManager>
    			
    			<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="com/zl/dao/carDaoMapper.xml"/>
    		<mapper resource="com/zl/dao/userDaoMapper.xml"/>
    		<mapper resource="com/zl/dao/brandDaoMapper.xml"/>
    		<mapper resource="com/zl/dao/powerDaoMapper.xml"/>
    		<mapper resource="com/zl/dao/roleDaoMapper.xml"/>
    	</mappers>	
    </configuration>

**userDaoMapper.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="com.zl.dao.CarDao">
    	
    	<resultMap type="car" id="carAndBrand">
    		
    		<id column="id" property="id"/>
    		
    		<result column="carId" property="carId"/>
    		<result column="color" property="color"/>
    		<result column="seat" property="seat"/>
    		<result column="youHao" property="youHao"/>
    		<result column="birDate" property="birDate"/>
    		<result column="riZhu" property="riZhu"/>
    		<result column="addDate" property="addDate"/>
    		<result column="img" property="img"/>
    		
    		<association property="brand" column="brandId" javaType="brand" select="com.zl.dao.BrandDao.queryBrandById"></association>
    		<association property="user" column="userId" javaType="user" select="com.zl.dao.UserDao.queryUserById"></association>
    	</resultMap>
    	 
    	
    	<select id="queryCarById" parameterType="int" resultType="car">
    		select * from car where id=#{id}
    	</select>
    	<delete id="deleteCar" parameterType="int">
    		delete from car where id=#{id}
    	</delete>
    	<insert id="addCar" parameterType="car">
    		insert into car (carId,brandId,color,seat,youHao,birDate,riZhu,addDate,userId,img) 
    			values(#{carId},#{brandId},#{color},#{seat},#{youHao},#{birDate},#{riZhu},#{addDate},#{userId},#{img})
    	</insert>
    	<update id="updateCar" parameterType="car">
    		update car set 
    			carId=#{carId},
    			brandId=#{brandId},
    			color=#{color},
    			seat=#{seat},
    			youHao=#{youHao},
    			birDate=#{birDate},
    			riZhu=#{riZhu},
    			addDate=#{addDate},
    			userId=#{userId},
    			img=#{img}
    		where id=#{id}
    	</update>
    	 <select id="queryCarByFy" parameterType="fy" resultMap="carAndBrand">
    	 	select * from (select c.*,rownum r from(select * from car 
    	 		
    	 		<where>
    	 			<if test="query!=null">
    	 				<if test="query.qColor!=null and query.qColor!=''">
    	 					and color like concat('%',concat(#{query.qColor},'%'))
    	 				</if>
    	 				<if test="query.brandId!=null and query.brandId!=0">
    	 					and brandid=#{query.brandId}
    	 				</if>
    	 				<if test="query.qStartBirDate!=null">
    	 					and birDate>#{query.qStartBirDate}
    	 				</if>
    	 				<if test="query.qEndBirDate!=null">
    	 					and birDate<![CDATA[<]]>#{query.qEndBirDate}
    	 				</if>
    	 			</if>
    	 		</where>
    	 	 ) c) where r>#{startRow} and r<![CDATA[<=]]>#{endRow}
    	 </select>
    	 <select id="queryRowCount" parameterType="query" resultType="int">
    	 	select count(*) from car 
    	 		<where>
     				<if test="qColor!=null and qColor!=''">
     					and color like concat('%',concat(#{qColor},'%'))
     				</if>
     				<if test="brandId!=null and brandId!=0">
     					and brandid=#{brandId}
     				</if>
     				<if test="qStartBirDate!=null">
     					and birDate>#{qStartBirDate}
     				</if>
     				<if test="qEndBirDate!=null">
     					and birDate<![CDATA[<]]>#{qEndBirDate}
     				</if>
    	 		</where>
    	 </select>
    </mapper>

**级联查询——集合属性**

[20181224191153713.png]: /images/20220403/820ab489ab5244d0ab4c611d27334281.png