mapper映射文件中用到的标签

mapper映射文件中标签的使用基本都出现在mapper映射文件中和测试使用的时候，这里先给大家展示标签的总结，接着是两个文件的代码

几个标签的总结：
                          if: <if test="条件">符合条件会做的事</if>
                          where: <where><if test="条件">符合条件会做的事</if></where>
                                                  where标签会自动补充where并且自动去掉第一个and
                          trim:               <trim prefix="要改为的前缀" prefixOverrides="要被改的前缀"
                                                  suffix="要改为的后缀" suffixOverrides="要被改的后缀"></trim>
                          set:                   <set><if test="条件">符合条件会做的事</if></set>
                                                  set标签会自动添加set并且自动去掉最后一个逗号
                          choose:                       类似于if(){}if(){}else，else{}
                                                               <choose>
                                                                   <when test="条件">
                                                                       符合条件就会执行，然后就不会执行后面的了
                                                                   </when>
                                                                   <when test="">
                                                                   </when>
                                                                   <otherwise>
                                                                   </otherwise>
                                                               </choose>
                          foreach: <foreach collection="" item="" open="" separator=""></foreach>
                                                   collection中的内容根据参数不同来写，数组用array，集合用list，别名的话就用别名；item是临时的对象变量

TeacherMapper.xml:

---------------------------------------代码开始---------------------------------------

<?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.dao.TeacherDAO">

       <select id="getTeaArray" resultType="teacher">
           select * from teacher
           
           <foreach collection="array" item="elm" open="where" separator="or">
                   teaName=#{elm.teaName}
           </foreach>
       </select>

       <select id="getTeaById" resultType="teacher">
           select * from teacher
           
           <choose>
               <when test="teaId!=0">
                   where teaId=#{teaId}
               </when>
               <when test="teaName!=null">
                   where teaName=#{teaName}
               </when>
               <otherwise>
               </otherwise>
           </choose>
       </select>
       <update id="update">
       
               update teacher
               
               <set>
                   <if test="teaName!=null">
                           teaName=#{teaName},
                       </if>
                       <if test="teaAge!=0">
                           teaAge=#{teaAge},
                       </if>
               </set>
               where teaId=#{teaId}
               
               
               <choose>
                   <when test="">

                   </when>
               </choose>
       </update>

       <select id="getTeaByMore" resultType="teacher">
               
               
               select * from teacher
               
               <trim prefix="where" prefixOverrides="and">
                       <if test="teaId!=0">
                           and teaId=#{teaId}
                       </if>
                       <if test="teaName!=null">
                           and teaName=#{teaName}
                       </if>
                       <if test="teaAge!=0">
                           and teaAge=#{teaAge}
                       </if>
               </trim>
               
               
               
               
</select>
</mapper>

---------------------------------------代码结束---------------------------------------

test.java

---------------------------------------代码开始---------------------------------------

package com.test;

import java.util.List;

import org.junit.Test;

import com.dao.TeacherDAO;
import com.dao.impl.TeacherDAOImpl;
import com.entity.Teacher;

public class TeacherDAOTest {

           @Test
           public void getTeaByMoreTest(){
               TeacherDAO dao=new TeacherDAOImpl();
               //对象tea一定要实现，否则不能使用
               Teacher tea=new Teacher();
               //字符串就是字符串，不能写成单引号字符
               tea.setTeaName("张四");
               List<Teacher> teaList=dao.getTeaByMore(tea);
               for(Teacher t:teaList){
                   System.out.println(t);
               }
           }
           //测试方法不要有返回值，否则报错，而又没有错误信息
           @Test
           public void updateTest(){
               TeacherDAO dao=new TeacherDAOImpl();
               Teacher tea=new Teacher();
               //别忘了选择学号
               tea.setTeaId(1);
               tea.setTeaAge(100);
               int count=dao.update(tea);
               System.out.println(count);
           }
           @Test
           public void getTeaByIdTest(){
               TeacherDAO dao=new TeacherDAOImpl();
               Teacher tea=new Teacher();
               tea.setTeaName("李四");
               //别忘了选择学号
               List<Teacher> teaList=dao.getTeaById(tea);
               for(Teacher t:teaList){
                   System.out.println(t);
               }
           }
           @Test
           public void getTeaArrayTest(){
               TeacherDAO dao=new TeacherDAOImpl();
               Teacher[] tea=new Teacher[2];
               //对象数组要对每一个数组元素进行再次初始化，否则会空指针错误
               tea[0]=new Teacher();
               tea[1]=new Teacher();
               tea[0].setTeaName("张四");
               tea[1].setTeaName("李四");
               List<Teacher> teaList=dao.getTeaArray(tea);
               for(Teacher t:teaList){
                   System.out.println(t);
               }
           }
}

---------------------------------------代码结束---------------------------------------

mapper映射文件中用到的标签

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