Mybatis高级映射分步查询之引入延迟加载提高查询性能-----Mybatis框架

客官°小女子只卖身不卖艺 2024-03-03 08:36 83阅读 0赞

>     分步查询的优点,可以重复利用,可复用性能增强,每一步的复用性较强
>     通过分步查询可以实现延迟加载和懒加载特性机制
>     延迟加载的核心原理是,用的时候执行查询语句,不用的时候不查询
>     作用:提高性能
>     笛卡尔积:3*4=12表越多,查询效率越低
>     咱们开启延迟加载呢?
>     association标签中添加fetchType="lazy"
>     默认情况下是没有开启延迟加载的
>     实际开发的程序是把全局的延迟加载打开,如果某一步不需要延迟加载,我们就为它单独设置eager
> 
>     分步查询的优点,可以重复利用,可复用性能增强,每一步的复用性较强
>     通过分步查询可以实现延迟加载和懒加载特性机制
>     延迟加载的核心原理是,用的时候执行查询语句,不用的时候不查询
>     作用:提高性能
>     笛卡尔积:3*4=12表越多,查询效率越低
>     咱们开启延迟加载呢?
>     association标签中添加fetchType="lazy"
>     默认情况下是没有开启延迟加载的
>     实际开发的程序是把全局的延迟加载打开,如果某一步不需要延迟加载,我们就为它单独设置eager

>     <?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.powernode.mybatis.mappers.StudentMapper">
>         <resultMap id="studentResultMapAssociation" type="student">
>             <id property="sid" column="sid"></id>
>             <result property="sname" column="sname"></result>
>     
>     
>             <association property="clazz" javaType="clazz">
>                 <id column="cid" property="cid"></id>
>                 <result property="cname" column="cname"></result>
>             </association>
>         </resultMap>
>         <resultMap id="studentResultMap" type="student">
>             <id property="sid" column="sid"></id>
>             <result property="sname" column="sname"></result>
>             <result property="clazz.cid" column="cid"></result>
>             <result property="clazz.cname" column="cname"></result>
>         </resultMap>
>         <select id="selectById" resultMap="studentResultMap">
>             select
>                 s.sid,s.sname,c.cid,c.cname
>             from
>                 t_stu as s left join t_clazz as c on s.cid = c.cid
>             where
>                 s.sid = #{sid};
>         </select>
>         <select id="selectByAssociation" resultMap="studentResultMapAssociation">
>             select
>                 s.sid,s.sname,c.cid,c.cname
>             from
>                 t_stu as s left join t_clazz as c on s.cid = c.cid
>             where
>                 s.sid = #{sid};
>         </select>
>         <select id="selectByIDStepOne" resultMap="studentResultMapByStep">
>             select sid,sname,cid from t_stu where sid = #{sid}
>         </select>
>     
>     
>     
>         <resultMap id="studentResultMapByStep" type="student">
>             <id property="sid" column="sid"></id>
>             <result property="sname" column="sname"></result>
>     
>     
>             <association property="clazz"
>                          select="com.powernode.mybatis.mappers.ClazzMapper.selectByIdStepTwo"
>                          fetchType="eager"
>                          column="cid"></association>
>         </resultMap>
>     </mapper>
> 
>     <?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.powernode.mybatis.mappers.StudentMapper">
>         <resultMap id="studentResultMapAssociation" type="student">
>             <id property="sid" column="sid"></id>
>             <result property="sname" column="sname"></result>
>     
>     
>             <association property="clazz" javaType="clazz">
>                 <id column="cid" property="cid"></id>
>                 <result property="cname" column="cname"></result>
>             </association>
>         </resultMap>
>         <resultMap id="studentResultMap" type="student">
>             <id property="sid" column="sid"></id>
>             <result property="sname" column="sname"></result>
>             <result property="clazz.cid" column="cid"></result>
>             <result property="clazz.cname" column="cname"></result>
>         </resultMap>
>         <select id="selectById" resultMap="studentResultMap">
>             select
>                 s.sid,s.sname,c.cid,c.cname
>             from
>                 t_stu as s left join t_clazz as c on s.cid = c.cid
>             where
>                 s.sid = #{sid};
>         </select>
>         <select id="selectByAssociation" resultMap="studentResultMapAssociation">
>             select
>                 s.sid,s.sname,c.cid,c.cname
>             from
>                 t_stu as s left join t_clazz as c on s.cid = c.cid
>             where
>                 s.sid = #{sid};
>         </select>
>         <select id="selectByIDStepOne" resultMap="studentResultMapByStep">
>             select sid,sname,cid from t_stu where sid = #{sid}
>         </select>
>     
>     
>     
>         <resultMap id="studentResultMapByStep" type="student">
>             <id property="sid" column="sid"></id>
>             <result property="sname" column="sname"></result>
>     
>     
>             <association property="clazz"
>                          select="com.powernode.mybatis.mappers.ClazzMapper.selectByIdStepTwo"
>                          fetchType="eager"
>                          column="cid"></association>
>         </resultMap>
>     </mapper>

>     <?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"/>
>         <settings>
>     
>             <setting name="lazyLoadingEnabled" value="true"/>
>             <setting name="mapUnderscoreToCamelCase" value="true"/>
>             <setting name="logImpl" value="SLF4J"/>
>         </settings>
>         <typeAliases>
>             <package name="com.powernode.mybatis.pojo"/>
>         </typeAliases>
>         <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>
>             <package name="com.powernode.mybatis.mappers"/>
>         </mappers>
>     </configuration>
> 
>     <?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"/>
>         <settings>
>     
>             <setting name="lazyLoadingEnabled" value="true"/>
>             <setting name="mapUnderscoreToCamelCase" value="true"/>
>             <setting name="logImpl" value="SLF4J"/>
>         </settings>
>         <typeAliases>
>             <package name="com.powernode.mybatis.pojo"/>
>         </typeAliases>
>         <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>
>             <package name="com.powernode.mybatis.mappers"/>
>         </mappers>
>     </configuration>

>     <?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.powernode.mybatis.mappers.ClazzMapper">
>         <select id="selectByIdStepTwo" resultType="clazz">
>             select cid,cname from t_clazz where cid = #{cid}
>         </select>
>     </mapper>
> 
>     <?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.powernode.mybatis.mappers.ClazzMapper">
>         <select id="selectByIdStepTwo" resultType="clazz">
>             select cid,cname from t_clazz where cid = #{cid}
>         </select>
>     </mapper>

>     package com.powernode.mybatis.mappers;
>     
>     import com.powernode.mybatis.pojo.Student;
>     
>     public interface StudentMapper
>     {
>         //分步查询第一步,根据SID查询学生信息
>         Student selectByIDStepOne(Integer id);
>         //使用Association的方式查询学生信息
>         Student selectByAssociation(Integer id);
>         //根据ID获取学生信息,获取学生关联的ID信息
>         Student selectById(Integer id);
>     }
> 
>     package com.powernode.mybatis.mappers;
>     
>     import com.powernode.mybatis.pojo.Student;
>     
>     public interface StudentMapper
>     {
>         //分步查询第一步,根据SID查询学生信息
>         Student selectByIDStepOne(Integer id);
>         //使用Association的方式查询学生信息
>         Student selectByAssociation(Integer id);
>         //根据ID获取学生信息,获取学生关联的ID信息
>         Student selectById(Integer id);
>     }

>     package com.powernode.mybatis.Test;
>     
>     import com.powernode.mybatis.mappers.StudentMapper;
>     import com.powernode.mybatis.pojo.Student;
>     import com.powernode.mybatis.utils.SqlSessionUtils;
>     import org.apache.ibatis.session.SqlSession;
>     import org.junit.Test;
>     import org.slf4j.Logger;
>     import org.slf4j.LoggerFactory;
>     
>     public class StudentMapperTest
>     {
>         private static final Logger logger = LoggerFactory.getLogger(StudentMapperTest.class);
>         @Test
>         public void selectById()
>         {
>             SqlSession sqlSession = SqlSessionUtils.openSession();
>             StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
>             Student student = mapper.selectById(1);
>             logger.info(student.toString());
>             SqlSessionUtils.close(sqlSession);
>         }
>         @Test
>         public void selectByAssociation()
>         {
>             SqlSession sqlSession = SqlSessionUtils.openSession();
>             StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
>             Student student = mapper.selectByAssociation(2);
>             logger.info(student.toString());
>             SqlSessionUtils.close(sqlSession);
>         }
>         @Test
>         public void selectByIdStepTwo()
>         {
>             SqlSession sqlSession = SqlSessionUtils.openSession();
>             StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
>             Student student = mapper.selectByIDStepOne(1);
>             logger.info(student.getSname().toString());
>             //程序执行到这里了,我想看看班级名字
>             logger.info(student.getClazz().getCname());
>             SqlSessionUtils.close(sqlSession);
>         }
>     }
> 
>     package com.powernode.mybatis.Test;
>     
>     import com.powernode.mybatis.mappers.StudentMapper;
>     import com.powernode.mybatis.pojo.Student;
>     import com.powernode.mybatis.utils.SqlSessionUtils;
>     import org.apache.ibatis.session.SqlSession;
>     import org.junit.Test;
>     import org.slf4j.Logger;
>     import org.slf4j.LoggerFactory;
>     
>     public class StudentMapperTest
>     {
>         private static final Logger logger = LoggerFactory.getLogger(StudentMapperTest.class);
>         @Test
>         public void selectById()
>         {
>             SqlSession sqlSession = SqlSessionUtils.openSession();
>             StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
>             Student student = mapper.selectById(1);
>             logger.info(student.toString());
>             SqlSessionUtils.close(sqlSession);
>         }
>         @Test
>         public void selectByAssociation()
>         {
>             SqlSession sqlSession = SqlSessionUtils.openSession();
>             StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
>             Student student = mapper.selectByAssociation(2);
>             logger.info(student.toString());
>             SqlSessionUtils.close(sqlSession);
>         }
>         @Test
>         public void selectByIdStepTwo()
>         {
>             SqlSession sqlSession = SqlSessionUtils.openSession();
>             StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
>             Student student = mapper.selectByIDStepOne(1);
>             logger.info(student.getSname().toString());
>             //程序执行到这里了,我想看看班级名字
>             logger.info(student.getClazz().getCname());
>             SqlSessionUtils.close(sqlSession);
>         }
>     }