Mybatis第三天

 1.动态sql语句

1. if

   <if test="条件">
   				
   </if>

   

    

2. where:在sql语句的开头加上where，并去除头部的and或or

   <where>
       <if test = “ ”>
       </if>
       <if test = “ ”>
       </if>
   </where>

   

    

3. set:在sql语句前添加set，并把sql语句中最后的”,”去除

   <set>
       <if test = “ ”>
       </if>
       <if test = “ ”>
       </if>
   </set>

   

    

4. trim:可以完成set或者是where标记的功能

   <trim prefix="前缀" prefixOverrides="去除的前缀" suffix="后缀" suffixOverrides="去除的后缀">		
   	<if test="">
   				
   	</if>
   	<if test="">
   				
   	</if>		
   </trim>

   

    

5. choose+when+otherwise

   <select>
       <where>
   	<choose>
   	    <when test="">
                   sql语句
   	    </when>
   	    <when test="">
                   sql语句
   	    </when>
   	    <otherwise>
                   sql语句
   	    </otherwise>
   	</choose>		
       </where>		
   </select>

   

    

6. SQL 片段

   <sql id="sql名">公共语句或字段</sql> //公共代码
   
   <include refid="sql名"/> //引用

   

    

7. foreach

   <select id="" resultType="">
       select <include refid="users"/>from users		
       <where>
           <!-- 防止集合为空 -->
   	<if test="ids.size()!=0">
   	    <!--
   	                collection:指定输入对象中的集合属性
   	                item:每次遍历生成的对象
   	                open:开始遍历时的拼接字符串
   	                close:结束时拼接的字符串
   	                separator:遍历对象之间需要拼接的字符串
   	                select * from user where id in (1,2,3)
              -->
   	   <foreach collection="ids" item="id" open="id in(" close=")" separator=",">
   		#{id}
   	   </foreach>
           </if>
       </where>	
   </select>

   

    

2.逆向工程(generator)

1. 下载jar包?

2. 配置逆向工程文件

   1. 在工程根目录下新建xml文件?
   2. 配置文件

      <?xml version="1.0" encoding="UTF-8"?>
      <!DOCTYPE generatorConfiguration
        PUBLIC "-//mybatis.org//DTD MyBatis Generator Configuration 1.0//EN"
        "http://mybatis.org/dtd/mybatis-generator-config_1_0.dtd">
      
      <generatorConfiguration>
        <!-- 路径是jar包的路径，最好路径不含中文 -->
        <classPathEntry location="E:\\java\\mybatis-generator-core-1.3.5.jar" />
      
        <context id="DB2Tables" targetRuntime="MyBatis3">
        
        	<!-- 是否去除逆向生成中的注释 true:是；false:否-->
          <commentGenerator>
              <property name="suppressAllComments" value="true" />
          </commentGenerator>
          
          <!-- 配置数据库连接信息 -->
          <jdbcConnection driverClass="com.mysql.jdbc.Driver"
              connectionURL="jdbc:mysql://localhost:3306/mybatis"
              userId="root"
              password="root">
          </jdbcConnection>
      
          <javaTypeResolver >
            <property name="forceBigDecimals" value="false" />
          </javaTypeResolver>
      
      	<!-- 实体类bean所在的位置 -->
          <javaModelGenerator targetPackage="com.zhiyou100.zfx.bean" targetProject="./src">
            <property name="enableSubPackages" value="true" />
            <property name="trimStrings" value="true" />
          </javaModelGenerator>
      
      	<!-- 映射文件mapper的位置 -->
          <sqlMapGenerator targetPackage="com.zhiyou100.zfx.mapper"  targetProject="./resources">
            <property name="enableSubPackages" value="true" />
          </sqlMapGenerator>
      
      	<!-- dao类所在位置 -->
          <javaClientGenerator type="XMLMAPPER" targetPackage="com.zhiyou100.zfx.dao"  targetProject="./src">
            <property name="enableSubPackages" value="true" />
          </javaClientGenerator>
      
      	<!-- 表与实体类 -->
          <table schema="mybatis" tableName="users" domainObjectName="Users"
          enableCountByExample="false" enableDeleteByExample="false" enableSelectByExample="false" enableUpdateByExample="false">
          <!-- Example结尾的最好用false,有些方法还是自己写为好 -->
            <property name="useActualColumnNames" value="true"/>
            <generatedKey column="ID" sqlStatement="DB2" identity="true" />
            <columnOverride column="DATE_FIELD" property="startDate" />
            <ignoreColumn column="FRED" />
            <columnOverride column="LONG_VARCHAR_FIELD" jdbcType="VARCHAR" />
          </table>
      
        </context>
        
      </generatorConfiguration>

      

       

   3. 编写java启动类，执行逆向工程的配置文件，生成数据库中指定表的bean和dao层

package com.zhiyou100.zfx.test;

import java.io.File;
import java.util.ArrayList;
import java.util.List;

import org.mybatis.generator.api.MyBatisGenerator;
import org.mybatis.generator.config.Configuration;
import org.mybatis.generator.config.xml.ConfigurationParser;
import org.mybatis.generator.internal.DefaultShellCallback;

public class test {

    public static void main(String[] args) throws Exception{
	List<String> warnings = new ArrayList<String>();
	boolean overwrite = true;
	File configFile = new File("generator.xml");
	ConfigurationParser cp = new ConfigurationParser(warnings);
	Configuration config = cp.parseConfiguration(configFile);
	DefaultShellCallback callback = new DefaultShellCallback(overwrite);
	MyBatisGenerator myBatisGenerator = new MyBatisGenerator(config, callback, warnings);
	myBatisGenerator.generate(null);
    }

}

3.分页助手(pageHelper)

1. 引入jar包?

2. 在配置文件conf.xml中添加?

3. dao类和相应的映射文件中要有查询方法

4. 编写测试类

   @Test
   void selectByPage() {
       //1.使用PageHelper类设置起始页和每页显示的页数
       int pageNum = 1;
       int pageSize = 3;		
       PageHelper.startPage(pageNum, pageSize);
   		
       //2.调用查询所有的方法
       List<Users> list = usersMapper.selectAll();
   		
       //3.把查询的结果封装到Pageinfo中
       PageInfo<Users> pageinfo = new PageInfo<>(list);
   		
       System.out.println(pageinfo);
   				
   }

   

    

Mybatis第三天

原文：https://www.cnblogs.com/zfx666/p/11438240.html