<mapper namespace="com.kangxg.mapper.UserMapper">  <select id="findUserWithOrders" parameterType = "Integer" resultMap="UserWithOrdersResult"> select u.*,o.id as orders_id,o.number from tb_user u,tb_orders o where u.id = o.user_id and u.id = #{id} </select> <resultMap type="com.kangxg.po.User" id="UserWithOrdersResult"> <id property = "id" column = "id"/> <result property = "username" column = "username"/> <result property = "address" column = "address"/> <collection property = "com.kangxg.po.ordersList" ofType = "Orders"> <id property ="id" column ="orders_id"/> <result property ="number" column = "number"/> </collection> </resultMap> </mapper> 对以上代码进行优化改错

查看订单的代码

mybatis-3-config.dtd mybatis-3-mapper.dtd

每个<mapper>元素代表一个数据库表，其中的<select>, <insert>, <update>, <delete>元素分别对应SQL的查询、插入、更新和删除操作。<resultMap>元素用于定义结果集映射，而<parameterMap>元素则用于...

mybatis-3.5.4.pdf

根据提供的文档信息，我们可以深入探讨MyBatis 3.5.4版本的相关知识点，包括其简介、安装步骤、配置方式以及基本用法等。 ### MyBatis 3.5.4概览 #### 1.1 什么是MyBatis？ **MyBatis**是一款优秀的一流持久层...

<?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="org.mybatis.example.BlogMapper"> <select id="selectStudentById" resultType="Student"> select * from s_student where id = #{id} </select> <select id="selectStudentByCId" resultType="Student"> select * from s_student where cid = #{cid} </select> <insert id="insertStudent" parameterType="Student" > insert into s_student(name,age,cid) values(#{name},#{age},#{cid}) </insert>

<select id="selectStudentsByClassName" resultType="Student"> SELECT s.* FROM s_student s JOIN s_class c ON s.cid = c.id WHERE c.name = #{className} </select> 2. 修改学生信息 <update id=...

<mapper namespace="com.quinta.mapper.StudentMapper"> <sql id="columns"> (id,name,age) </sql> <sql id="insertcolumns"> (#{id},#{name},#{age}) </sql> <resultMap id="StudentMap" type="com.quinta.pojo.Student"> <id property="id" column="id"/> <result property="age" column="age"/> <result property="name" column="name"/> </resultMap> <select id="SelectById" resultType="com.quinta.pojo.Student"> select <include refid="columns"/> from student2 where id = #{id}; </select> <select id="SelectAll" resultMap="StudentMap"> select * from student2; </select> <insert id="addStudent"> insert into student2

<mapper namespace="com.example.UserMapper"> <select id="selectUserById" resultType="User"> SELECT * FROM user WHERE id = #{userId} </select> </mapper> - namespace 对应 Java 接口的全限定名 - ...

<mapper namespace="com.example.YourMapper"> <insert id="batchInsertOrUpdate" parameterType="java.util.List"> <foreach collection="list" item="item" separator=";"> <if test="item.id != null"> SELECT COUNT(*) FROM your_table WHERE id = #{item.id} </if> <choose> <when test="_parameter[0] > 0"> UPDATE your_table SET column1 = #{item.column1}, column2 = #{item.column2} WHERE id = #{item.id} </when> <otherwise> INSERT INTO your_table (id, column1, column2) VALUES (#{item.id}, #{item.column1}, #{item.column2}) </otherwise> </choose> </foreach> </insert> </mapper>和mybatis-plus的saveOrUpdateBatch性能比较及如何选用

- 性能比较：使用<insert>标签进行大批量数据操作时，会根据每个数据的ID是否存在执行对应的更新或插入操作。这种方式对于数据量较小的情况下性能较好，因为它会逐条执行SQL语句。但是对于大批量数据操作来说，...

<mapper namespace="com.example.YourMapper"> <insert id="batchInsertOrUpdate" parameterType="java.util.List"> <foreach collection="list" item="item" separator=";"> <if test="item.id != null"> SELECT COUNT(*) FROM your_table WHERE id = #{item.id} </if> <choose> <when test="_parameter[0] > 0"> UPDATE your_table SET column1 = #{item.column1}, column2 = #{item.column2} WHERE id = #{item.id} </when> <otherwise> INSERT INTO your_table (id, column1, column2) VALUES (#{item.id}, #{item.column1}, #{item.column2}) </otherwise> </choose> </foreach> </insert> </mapper>和mybatis-plus的saveOrUpdateBatch性能比较及如何选用，注：实体对象ID属于type = IdType.INPUT非自增

- 性能比较：使用<insert>标签进行大批量数据操作时，会根据每个数据的ID是否存在执行对应的更新或插入操作。这种方式对于数据量较小的情况下性能较好，因为它会逐条执行SQL语句。但是对于大批量数据操作来说，...

这是我项目中的UserMapper.xml代码：<?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="org.huse.pojo.User"> <select id="findById" parameterType="int" resultType="org.huse.pojo.User"> select id, username, age from users where id = #{id} </select> </mapper>还应该加些什么

在UserMapper.xml中添加基础的增删改查语句，需定义<select>, <insert>, <update>, <delete>标签，并绑定到Mapper接口方法： xml  <select id="selectUserById" resultType=...

<select id="getMemberById" parameterType="int" resultType="com.itheima.entity.Member" useCache="false" flushCache="true"> SELECT * FROM ms_member WHERE member_id = #{id} </select>用这个方法如何修改？<?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> <settings> <setting name="logImpl" value="STDOUT_LOGGING"/> <setting name="mapUnderscoreToCamelCase" value="true"/> </settings> <environments default="development"> <environment id="development"> <transactionManager type="JDBC"/> <dataSource type="POOLED"> </dataSource> </environment> </environments> <mappers> <mapper resource="com/itheima/mapper/MemberDaoMapper.xml" /> <mapper resource="com/itheima/mapper/EmployeeMapper.xml" /> <mapper resource="com/itheima/mapper/IdCardMapper.xml" /> <mapper resource="com/itheima/mapper/DeptMapper.xml" /> </mappers> </configuration>给出完整的代码。

--指定mapper文件的位置--><mapperresource="mapper/MemberDao.xml"/></mappers></configuration>或者，如果使用包扫描的方式（要求Mapper.xml文件与接口在同一包下）：xml<mappers><packagename="cyt.mybatis...

根据下面的配置信息，写出Classes，Teacher和Student这三个POJO的全部代码。<mapper namespace="com.lcb.mapping.userMapper"> <l--association—对—关联查询--> <select id="getClass" parameterType="int" resultMap="ClassesResultMap">select * from class c,teacher t where c.teacher_id=t.t_id and c.c_id=#{id} <select> <resultMap type="com.lcb.user.Classes" id="ClassesResultMap"><l--实体类的字段名和数据表的字段名映射--> <id property="id" column="c_id"/> <result property="name" column="c_name"/><association property="teacher" javaType="com.Icb.user.Teacher"><id property="id" column="t_id" l> <result property="name" column="t_name"/></association> </resultMap> <l--collection—对多关联查询--> <select id="getClass2" parameterType="int"resultMap="ClassesResultMap2"> select * from class c,teacher t,student s where c.teacher_id=t.t_idand c.c_id=s.class_id and c.c_id=#{ id} <select> <resultMap type="com.lcb.user.Classes" id="ClassesResultMap2"><id property=""id" column="c_id"/> <result property="name" column="c_name"/><association property="teacher" javaType="com.Icb.user.Teacher"><id property="id" column="t_id"l> <result property="name" column="t_name"/></association> <collection property="student" ofType="com.Icb.user.Student"><id property="id" column="s_id"/> cresult property="name" column="s_name"/></collection> </resultMap></mapper>

private int id; private String name; private int teacherId; private Teacher teacher; // 省略getter和setter方法 } 2. Teacher POJO代码： public class Teacher { private int id; private String ...

<mapper namespace="com.example.ordermgmt.auth.mapper.UserMapper"> <resultMap id="UserResultMap" type="User"> <id property="userId" column="user_id"/> <result property="username" column="user_name"/> <result property="password" column="user_password"/> <result property="ip" column="user_ip"/> <result property="power" column="user_power" typeHandler="org.apache.ibatis.type.EnumOrdinalTypeHandler"/> </resultMap> <select id="selectByUsername" resultMap="UserResultMap"> SELECT * FROM user WHERE user_name = #{username} </select> </mapper>这一段语法对吗，是否应该大写

根据引用[1]，<select>标签中可以写SQL语句，包括模糊查询。比如检查id是否唯一，parameterType是否正确，resultType或resultMap是否配置。这里需要注意resultMap的引用是否正确，比如引用[3]中的例子，association...

下面代码中的user是什么？在IDEA环境下，如何创造这样一个“user”？代码：<?xml version="1.0" encoding="UTF-8" ?><!DOCTYPE mapperPUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""http://mybatis.org/dtd/mybatis-3-mapper.dtd"><mapper namespace="com.example.demo.mapper.UserMapper"> <resultMap id="userMap" type="com.example.demo.entity.User"> <id column="id" property="id"/> <result column="name" property="name"/> <result column="age" property="age"/> <result column="gender" property="gender"/> </resultMap> <select id="selectById" resultMap="userMap"> select * from user where id = #{id} </select> <select id="selectAll" resultMap="userMap"> select * from user </select> <insert id="insert" parameterType="com.example.demo.entity.User"> insert into user(name, age, gender) values(#{name}, #{age}, #{gender}) </insert> <update id="update" parameterType="com.example.demo.entity.User"> update user set name = #{name}, age = #{age}, gender = #{gender} where id = #{id} </update> <delete id="deleteById"> delete from user where id = #{id} </delete></mapper>

在这个XML文件中，"user"是一个数据库表的实体类，包含了id、name、age、gender等字段。这里的"user"并不是IDEA环境下创建的对象，而是代表了数据库表的实体类，需要在Java代码中创建对应的实体类。在IDEA环境下...

解释代码<?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.synu.sx.demo.mapper.StudentMapper"> <select id="list" parameterType="java.util.Map" resultType="com.synu.sx.demo.entity.Student"> select * from student <where> <if test="param.id != null and param.id != ''"> id = #{param.id} </if> </where> </select> <select id="listQuery" parameterType="java.util.Map" resultType="com.synu.sx.demo.entity.Student"> select * from student <where> <if test="param.name != null and param.name != ''"> and name like concat('%', #{param.name} ,'%') </if> <if test="param.id != null and param.id != ''"> and id like concat('%', #{param.id} ,'%') </if> </where> limit #{param.start}, #{param.limit} </select> <select id="listQueryCount" parameterType="java.util.Map" resultType="java.lang.Integer"> select count(*) from student <where> <if test="param.name != null and param.name != ''"> and name like concat('%', #{param.name} ,'%') </if> <if test="param.id != null and param.id != ''"> and id like concat('%', #{param.id} ,'%') </if> </where> </select> </mapper>

在<if>标签中，如果param的id属性不为空，则添加了一个id = #{param.id}的条件。第二个查询语句的id是"listQuery"，与第一个查询语句类似，不同之处在于它添加了更多的条件筛选和分页功能。除了id之外，它还检查了...

<?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.example.mapper.StudentMapper"> <select id="queryStudentByConditions" parameterType="map" resultType="student"> select * from student <where> <if test="name != null and name != ''"> name = #{name} </if> <if test="name == null or name == '' and major != null and major != ''"> major = #{major} </if> <if test="name == null or name == '' and major == null or major == ''"> student_number is not null </if> </where> </select> <select id="queryStudentByIdLessThanFive" resultType="student"> select * from student where id < 5 </select> <select id="queryStudentsByCourses" resultType="student"> select s.* from student s join student_course sc on s.id = sc.student_id where sc.course_name in ('数学', '化学', '物理') group by s.id having count(distinct sc.course_name) = 3 </select> <update id="updateMajorForZhangFei"> update student <set> major = '计算机' </set> where name = '张飞' </update> </mapper> import org.apache.ibatis.session.SqlSession; import org.junit.Test; import java.util.HashMap; import java.util.List; import java.util.Map; public class StudentTest { @Test public void queryStudentByConditionsTest() { SqlSession sqlSession = MyBatisUtil.getSqlSession(); try { // 模拟不同的查询条件 Map<String, Object> params = new HashMap<>(); // 条件1：只输入姓名 params.put("name", "张三"); List<Student> students1 = sqlSession.getMapper(StudentMapper.class).queryStudentByConditions(params); // 条件2：只输入专业 params.clear(); params.put("major", "计算机科学"); List<Student> students2 = sqlSession.getMapper(StudentMapper.class).queryStudentByConditions(params); // 条件3：姓名和专业都为空 params.clear(); List<Student> students3 = sqlSession.getMapper(StudentMapper.class).queryStudentByConditions(params); // 输出结果 System.out.println("条件1查询结果：" + students1); System.out.println("条件2查询结果：" + students2); System.out.println("条件3查询结果：" + students3); } finally { sqlSession.close(); } } @Test public void queryStudentByIdLessThanFiveTest() { SqlSession sqlSession = MyBatisUtil.getSqlSession(); try { List<Student> students = sqlSession.getMapper(StudentMapper.class).queryStudentByIdLessThanFive(); System.out.println("id小于5的学生信息：" + students); } finally { sqlSession.close(); } } @Test public void queryStudentsByCoursesTest() { SqlSession sqlSession = MyBatisUtil.getSqlSession(); try { List<Student> students = sqlSession.getMapper(StudentMapper.class).queryStudentsByCourses(); System.out.println("选修了数学、化学、物理的学生：" + students); } finally { sqlSession.close(); } } @Test public void updateMajorForZhangFeiTest() { SqlSession sqlSession = MyBatisUtil.getSqlSession(); try { int count = sqlSession.getMapper(StudentMapper.class).updateMajorForZhangFei(); System.out.println("受影响的行数：" + count); sqlSession.commit(); } finally { sqlSession.close(); } } } 在上述代码运行成功后生成在idea里边运行代码成功的截图

<select id="queryStudentByConditions" ... > select * from student <where> ... </where> - 根据传入的 name 和 major 参数动态拼接SQL。 - 使用 <if> 判断是否添加相应条件。 2. **单条件...

解释一下这段代码：<?xml version = "1.0" encoding = "UTF-8"?> <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD com.example.Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd"> <mapper namespace="com.example.demo.mapper.UserMapper"> <resultMap id="result" type="com.example.demo.entity.User"> <result property="userId" column="userId" /> <result property="userDate" column="userDate" /> <result property="userName" column="userName" /> <result property="userAddress" column="userAddress"/> </resultMap> <select id="ListUser" resultMap="result"> SELECT * FROM user </select> <select id="findUserByName" resultMap="result" parameterType="String"> SELECT * FROM user where userName like concat(concat('%',#{userName}),'%') order by userId desc </select> <select id="queryPage" resultMap="result" parameterType="Integer"> select * from user order by userId desc limit #{startRows},5 </select> <select id="getRowCount" resultType="Integer"> select count(*) from user </select> <insert id="insertUser" parameterType="com.example.demo.entity.User"> INSERT INTO user ( userId,userDate,userName,userAddress ) VALUES ( #{userId}, #{userDate, jdbcType=VARCHAR}, #{userName, jdbcType=VARCHAR}, #{userAddress, jdbcType=VARCHAR} ) </insert> <delete id="delete" parameterType="int"> delete from user where userId=#{userId} </delete> <update id="Update" parameterType="com.example.demo.entity.User"> update user set user.userDate=#{userDate},user.userName=#{userName},user.userAddress=# {userAddress} where user.userId=#{userId} </update> </mapper>

- <mapper namespace="com.example.demo.mapper.UserMapper">：指定了映射文件的命名空间，即该文件中定义的SQL语句与Java方法的映射关系将归属于com.example.demo.mapper.UserMapper这个命名空间。 - <resultMap>：...

<?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.atguigu.springcloud.dao.PaymentDao"> <insert id="create" parameterType="payment" useGeneratedKeys="true" keyProperty="id"> insert into payment(serial) values(#{serial}) </insert> <resultMap id="BaseResultMap" type="com.atguigu.springcloud.entities.Payment"> <id column="id" property="id" jdbcType="BIGINT"/> <id column="serial" property="serial" jdbcType="VARCHAR"/> </resultMap> <select id="getPaymentById" parameterType="Long" resultMap="BaseResultMap"> select * from payment where id=#{id} </select> </mapper>

这是一个使用MyBatis框架编写...查询语句从payment表中根据id进行查询。 BaseResultMap定义了结果映射的规则，将查询结果的id和serial分别映射到对应的属性上，其中id的JDBC类型是BIGINT，serial的JDBC类型是VARCHAR。

<?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="org.pojo.UesrinfoMapper"> <select id="froUser" parameterType="Integer" resultType="org.pojo.Uesrinfo"> select * from uesrinfo </select> <insert id="intoUser" parameterType="org.pojo.Uesrinfo"> insert into uesrinfo(username,password,boo) values (#{username},#{password},#{boo}) </insert> <update id="updtUser" parameterType="org.pojo.Uesrinfo"> update uesrinfo set username=#{username},password=#{password},boo=#{boo} where id=#{id} </update> <delete id="deltUser" parameterType="Integer"> delete from uesrinfo where order=#{id} </delete> </mapper>

<select id="froUser" parameterType="Integer" resultType="org.pojo.Uesrinfo"> select * from userinfo </select> <insert id="intoUser" parameterType="org.pojo.Uesrinfo"> insert into userinfo...

<?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.itheima.mapper.StudentMapper"> <resultMap type="com.itheima.pojo.Student" id="studentMap"> <id property="id" column="sid"/> <result property="name" column="sname"/> <result property="age" column="sage"/> </resultMap> <select id="findAllStudent" resultMap="studentMap"> select * from t_student </select> </mapper>我的studenmapper代码是这个请直接给我修改之后的代码

-- 根据学号查询学生信息 --> <select id="findStudentByStuno" parameterType="Integer" resultType="cn.edu.example.mybatis.po.Student"> SELECT * FROM t_student WHERE stuno = #{stuno} </select> <!-- ...

<mapper namespace="com. dao.BaoxiuxinxiDao"> <！一-可根据自己的需求，是否要使用--> <resultMap type="com. entity.BaoxiuxinxiEntity" id-"baoxiuxinxiMap"> <result property="weixiudanhao" column="weixiudanhao"/> <result property="loudonghao" column="loudonghao"/> <result property="menpaihao" column="menpaihao"/> <result property="baoxiumingcheng" column="baoxiumingcheng"/> <result property-"tupian" column="tupian"/> <result property="wentimiaoshu" column="wentimiaoshu"/> <result property="baoxiuriqi" column="baoxiuriqi"/> <result property="yezhuhao" column="yezhuhao"/> <result property="yezhuxingming" column="yezhuxingming"/> <result property="lianxidianhua" column="lianxidianhua"/> <result property="zhuangtai" column="zhuangtai"/> </resultMap> ▼<select id="selectListVo" resultType="com. entity.vo. Baoxiuxinxivo"> SELECT * FROM baoxiuxinxi baoxiuxinxi <where> 1=1 ${ew.sqlSegment}</where> </select> <select id="selectvo" resultType="com. entity.vo.Baoxiuxinxivo"> SELECT baoxiuxinxi.* FROM baoxiuxinxi baoxiu

<think>好的，用户想分析MyBatis的Mapper配置文件，特别是resultMap、select语句和SQL结构。首先，我需要回顾之前给他的回答，确保这次的信息是连贯的。之前我提到了namespace的配置、ResultMap的要点、SQL语句结构...

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