JavaWeb_(Mybatis框架)动态sql_七

 

 

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　　1、if标签 - 多条件查询，获取用户列表；　　
　　2、where标签 - 解决if标签拼接字符串AND符号问题；
　　3、trim标签 - 定制where标签的规则
　　4、set标签 - 解决更新数据表时字符串拼接逗号”,”问题；
　　5、foreach标签 – 如果需要使用IN查询多条相同数据，可以使用foreach遍历；
　　6、sql标签 – 可以提取重复sql语句片段；

 

1、if标签 - 多条件查询，获取用户列表

　　模糊查询用户名中带有"王"字的用户

　　UserMapper.java中编写通过用户模糊查询用户列表接口selectUserListByUser()

package com.Gary.mapper;

import java.util.List;

import com.Gary.bean.User;
import com.Gary.bean.UserVo;

public interface UserMapper {

    //通过id查询一个用户
    public User selectUserById(Integer id);
    
    //通过用户名模糊查询 获取用户列表
    public List<User> selectUserByName(String name);
    
    //通过UserVo id 查询一个用户
    public User selectUserByVoId(UserVo id);
    
    //查询用户总条数
    public Integer selectUserCount();
    
    //查询所有用户的包装类
    public List<UserVo> selectAllUserVo();
    
    //多条件查询  通过用户对象中的条件查询用户列表
    public List<User> selectUserListByUser(User u);
    
    
    
}

 

　　UserMapper.xml中实现这个模糊查询的方法

<select id="selectUserListByUser" parameterType="User" resultType="User">
         <!-- 查询用户性别 模糊用户名 查询用户cid 国际ID -->
         SELECT * FROM user WHERE u_sex = #{u_sex} 
                  AND u_username like "%"#{u_username}"%"
                  AND u_cid = #{u_cid}
     </select>

 

<?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.Gary.mapper.UserMapper">
 
     <select id="selectUserById" parameterType="Integer" resultType="user">
         select * from user where u_id = #{id}
     </select>
     
     <!-- #{}占位符 尽量使用#{}来解决问题 -->
     <!-- ${}字符串拼接   容易sql注入 (or 1 = 1) -->
     
     <!-- ${value}中间的字符串一定需要使用value -->
     <select id="selectUserByName" parameterType="String" resultType="com.Gary.bean.User">
         <!-- select * from user where u_username like '%${value}%' -->
              select * from user where u_username like "%"#{name}"%"
     </select>
     
     <!-- 添加用户 参数为全包名 -->
     <insert id="insertUser" parameterType="com.Gary.bean.User">
         insert into user values(null,#{u_username},#{u_password},#{u_sex},#{u_createTime},#{u_cid})
     </insert>
     
    <!-- 根据id修改username字段的语句 -->
     <update id="updateUser" parameterType="com.Gary.bean.User">
         update user set u_username = #{u_username} where u_id = #{u_id}
     </update>
     
     <!-- 根据id删除用户 -->
     <delete id="deleteUserById" parameterType="Integer">
         delete from user where u_id = #{id}
     </delete>
     
     <!-- 根据UserVo中的User对象的u_id去查询查询用户 -->
     <select id="selectUserByVoId" parameterType="UserVo" resultType="user">
         select * from user where u_id = #{user.u_id}
     </select>
     
     <!-- 查询用户的总条数 -->
     <select id="selectUserCount" resultType="Integer">
         select count(*) from user
     </select>
     
     <!-- 查询所有用户包装类 -->
     <resultMap type="UserVo" id="uservolist">
         <!-- 必须把想要查询数据库的语句都写上 -->
         <id property="u_id" column="u_id"/>
         <id property="u_username" column="u_username"/>
         <id property="u_sex" column="u_sex"/>
         <association property="country" javaType="Country">
             <!-- 必须把想要查询数据库的语句都写上 -->
             <result property="id" column="c_id"/>
             <result property="c_countryname" column="c_countryname"/>
         </association>
     </resultMap>
     
     <select id="selectAllUserVo" resultMap="uservolist">
         SELECT * FROM USER u LEFT JOIN country c ON u.u_cid = c.c_id
     </select>

         
     <select id="selectUserListByUser" parameterType="User" resultType="User">
         <!-- 查询用户性别 模糊用户名 查询用户cid 国际ID -->
         SELECT * FROM user WHERE u_sex = #{u_sex} 
                  AND u_username like "%"#{u_username}"%"
                  AND u_cid = #{u_cid}
     </select>
     
     
     
</mapper>


 
 

 

 

package com.Gary.test;

import java.io.IOException;
import java.io.InputStream;
import java.util.List;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Test;

import com.Gary.bean.Country;
import com.Gary.bean.CountryVo;
import com.Gary.bean.User;
import com.Gary.bean.UserVo;
import com.Gary.mapper.CountryMapper;
import com.Gary.mapper.UserMapper;

public class MapperTest8 {  

    @Test
    public void Test8() throws IOException {
        //读取配置文件
        String resource = "sqlMapConfig.xml";
                
        InputStream in = Resources.getResourceAsStream(resource);
                
        //创建sqlSessionFactory
        SqlSessionFactory ssf = new SqlSessionFactoryBuilder().build(in);
                
        //生产一个sqlSession
        SqlSession session = ssf.openSession();
                
        UserMapper mapper = session.getMapper(UserMapper.class);
        User u = new User();
        u.setU_sex("1");
        u.setU_username("王");
        u.setU_cid(1);
        
        List<User> list = mapper.selectUserListByUser(u);
        
        for(User user : list){
            System.out.println(user);
        }
        
    }
    
}

 

　　但此时，如果用户未输入三个参数，只输入了sex、username两个参数

    UserMapper mapper = session.getMapper(UserMapper.class);
    User u = new User();
    u.setU_sex("1");
    u.setU_username("王");
    //u.setU_cid(1);
        
    List<User> list = mapper.selectUserListByUser(u);
        
    for(User user : list){
        System.out.println(user);
    }    

 

　　此时会无法准确模糊查询到数据库中的值

 

package com.Gary.test;

import java.io.IOException;
import java.io.InputStream;
import java.util.List;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Test;

import com.Gary.bean.Country;
import com.Gary.bean.CountryVo;
import com.Gary.bean.User;
import com.Gary.bean.UserVo;
import com.Gary.mapper.CountryMapper;
import com.Gary.mapper.UserMapper;

public class MapperTest8 {  

    @Test
    public void Test8() throws IOException {
        //读取配置文件
        String resource = "sqlMapConfig.xml";
                
        InputStream in = Resources.getResourceAsStream(resource);
                
        //创建sqlSessionFactory
        SqlSessionFactory ssf = new SqlSessionFactoryBuilder().build(in);
                
        //生产一个sqlSession
        SqlSession session = ssf.openSession();
                
        UserMapper mapper = session.getMapper(UserMapper.class);
        User u = new User();
        u.setU_sex("1");
        u.setU_username("王");
        //u.setU_cid(1);
        
        List<User> list = mapper.selectUserListByUser(u);
        
        for(User user : list){
            System.out.println(user);
        }
        
    }
    
}

 

　　为防止照成这种情况，可以使用在查询时使用<if>标签【也可以防止用户添加空串】

<select id="selectUserListByUser" parameterType="User" resultType="User">
         <!-- 查询用户性别 模糊用户名 查询用户cid 国际ID -->
         SELECT * FROM user WHERE 
         
             <if test="u_sex != null">
                 u_sex = #{u_sex} 
             </if>
             
             <if test="u_username != null">
                 AND u_username like "%"#{u_username}"%"
             </if>
             
             <if test="u_cid != null">
                 AND u_cid = #{u_cid}
             </if>
     </select>

 

<?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.Gary.mapper.UserMapper">
 
     <select id="selectUserById" parameterType="Integer" resultType="user">
         select * from user where u_id = #{id}
     </select>
     
     <!-- #{}占位符 尽量使用#{}来解决问题 -->
     <!-- ${}字符串拼接   容易sql注入 (or 1 = 1) -->
     
     <!-- ${value}中间的字符串一定需要使用value -->
     <select id="selectUserByName" parameterType="String" resultType="com.Gary.bean.User">
         <!-- select * from user where u_username like '%${value}%' -->
              select * from user where u_username like "%"#{name}"%"
     </select>
     
     <!-- 添加用户 参数为全包名 -->
     <insert id="insertUser" parameterType="com.Gary.bean.User">
         insert into user values(null,#{u_username},#{u_password},#{u_sex},#{u_createTime},#{u_cid})
     </insert>
     
    <!-- 根据id修改username字段的语句 -->
     <update id="updateUser" parameterType="com.Gary.bean.User">
         update user set u_username = #{u_username} where u_id = #{u_id}
     </update>
     
     <!-- 根据id删除用户 -->
     <delete id="deleteUserById" parameterType="Integer">
         delete from user where u_id = #{id}
     </delete>
     
     <!-- 根据UserVo中的User对象的u_id去查询查询用户 -->
     <select id="selectUserByVoId" parameterType="UserVo" resultType="user">
         select * from user where u_id = #{user.u_id}
     </select>
     
     <!-- 查询用户的总条数 -->
     <select id="selectUserCount" resultType="Integer">
         select count(*) from user
     </select>
     
     <!-- 查询所有用户包装类 -->
     <resultMap type="UserVo" id="uservolist">
         <!-- 必须把想要查询数据库的语句都写上 -->
         <id property="u_id" column="u_id"/>
         <id property="u_username" column="u_username"/>
         <id property="u_sex" column="u_sex"/>
         <association property="country" javaType="Country">
             <!-- 必须把想要查询数据库的语句都写上 -->
             <result property="id" column="c_id"/>
             <result property="c_countryname" column="c_countryname"/>
         </association>
     </resultMap>
     
     <select id="selectAllUserVo" resultMap="uservolist">
         SELECT * FROM USER u LEFT JOIN country c ON u.u_cid = c.c_id
     </select>

         
     <select id="selectUserListByUser" parameterType="User" resultType="User">
         <!-- 查询用户性别 模糊用户名 查询用户cid 国际ID -->
         SELECT * FROM user WHERE 
         
             <if test="u_sex != null">
                 u_sex = #{u_sex} 
             </if>
             
             <if test="u_username != null">
                 AND u_username like "%"#{u_username}"%"
             </if>
             
             <if test="u_cid != null">
                 AND u_cid = #{u_cid}
             </if>
     </select>
     
     
     
</mapper>


 
 

 

 

package com.Gary.test;

import java.io.IOException;
import java.io.InputStream;
import java.util.List;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Test;

import com.Gary.bean.Country;
import com.Gary.bean.CountryVo;
import com.Gary.bean.User;
import com.Gary.bean.UserVo;
import com.Gary.mapper.CountryMapper;
import com.Gary.mapper.UserMapper;

public class MapperTest8 {  

    @Test
    public void Test8() throws IOException {
        //读取配置文件
        String resource = "sqlMapConfig.xml";
                
        InputStream in = Resources.getResourceAsStream(resource);
                
        //创建sqlSessionFactory
        SqlSessionFactory ssf = new SqlSessionFactoryBuilder().build(in);
                
        //生产一个sqlSession
        SqlSession session = ssf.openSession();
                
        UserMapper mapper = session.getMapper(UserMapper.class);
        User u = new User();
        u.setU_sex("1");
        u.setU_username("王");
        //u.setU_cid(1);
        
        List<User> list = mapper.selectUserListByUser(u);
        
        for(User user : list){
            System.out.println(user);
        }
        
    }
    
}

 

 　　此时如果是未输入第一个u_sex值，会产生bug，数据库执行语句就会变成 SELECT * FROM user WHERE  AND u_username like "%"#{u_username}"%"

 

<?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.Gary.mapper.UserMapper">
 
     <select id="selectUserById" parameterType="Integer" resultType="user">
         select * from user where u_id = #{id}
     </select>
     
     <!-- #{}占位符 尽量使用#{}来解决问题 -->
     <!-- ${}字符串拼接   容易sql注入 (or 1 = 1) -->
     
     <!-- ${value}中间的字符串一定需要使用value -->
     <select id="selectUserByName" parameterType="String" resultType="com.Gary.bean.User">
         <!-- select * from user where u_username like '%${value}%' -->
              select * from user where u_username like "%"#{name}"%"
     </select>
     
     <!-- 添加用户 参数为全包名 -->
     <insert id="insertUser" parameterType="com.Gary.bean.User">
         insert into user values(null,#{u_username},#{u_password},#{u_sex},#{u_createTime},#{u_cid})
     </insert>
     
    <!-- 根据id修改username字段的语句 -->
     <update id="updateUser" parameterType="com.Gary.bean.User">
         update user set u_username = #{u_username} where u_id = #{u_id}
     </update>
     
     <!-- 根据id删除用户 -->
     <delete id="deleteUserById" parameterType="Integer">
         delete from user where u_id = #{id}
     </delete>
     
     <!-- 根据UserVo中的User对象的u_id去查询查询用户 -->
     <select id="selectUserByVoId" parameterType="UserVo" resultType="user">
         select * from user where u_id = #{user.u_id}
     </select>
     
     <!-- 查询用户的总条数 -->
     <select id="selectUserCount" resultType="Integer">
         select count(*) from user
     </select>
     
     <!-- 查询所有用户包装类 -->
     <resultMap type="UserVo" id="uservolist">
         <!-- 必须把想要查询数据库的语句都写上 -->
         <id property="u_id" column="u_id"/>
         <id property="u_username" column="u_username"/>
         <id property="u_sex" column="u_sex"/>
         <association property="country" javaType="Country">
             <!-- 必须把想要查询数据库的语句都写上 -->
             <result property="id" column="c_id"/>
             <result property="c_countryname" column="c_countryname"/>
         </association>
     </resultMap>
     
     <select id="selectAllUserVo" resultMap="uservolist">
         SELECT * FROM USER u LEFT JOIN country c ON u.u_cid = c.c_id
     </select>

         
     <select id="selectUserListByUser" parameterType="User" resultType="User">
         <!-- 查询用户性别 模糊用户名 查询用户cid 国际ID -->
         SELECT * FROM user WHERE 
         
             <if test="u_sex != null">
                 u_sex = #{u_sex} 
             </if>
             
             <if test="u_username != null">
                 AND u_username like "%"#{u_username}"%"
             </if>
             
             <if test="u_cid != null">
                 AND u_cid = #{u_cid}
             </if>
     </select>
     
     
     
</mapper>


 
 

 

　　所以，为了解决上面这种情况，我们可以where标签

 

 

2、where标签 - 解决if标签拼接字符串AND符号问题；

　　在原有的selectUserListByUser查询用户性别 模糊用户名 查询用户cid 国际ID上添加<where>标签 <where>标签可以去掉前边的AND符号

     <select id="selectUserListByUser" parameterType="User" resultType="User">
         <!-- 查询用户性别 模糊用户名 查询用户cid 国际ID -->
         SELECT * FROM user 
             <where>
             <if test="u_sex != null">
                 u_sex = #{u_sex} 
             </if>
             
             <if test="u_username != null">
                 AND u_username like "%"#{u_username}"%"
             </if>
             
             <if test="u_cid != null">
                 AND u_cid = #{u_cid}
             </if>
             </where>
     </select>

 

<?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.Gary.mapper.UserMapper">
 
     <select id="selectUserById" parameterType="Integer" resultType="user">
         select * from user where u_id = #{id}
     </select>
     
     <!-- #{}占位符 尽量使用#{}来解决问题 -->
     <!-- ${}字符串拼接   容易sql注入 (or 1 = 1) -->
     
     <!-- ${value}中间的字符串一定需要使用value -->
     <select id="selectUserByName" parameterType="String" resultType="com.Gary.bean.User">
         <!-- select * from user where u_username like '%${value}%' -->
              select * from user where u_username like "%"#{name}"%"
     </select>
     
     <!-- 添加用户 参数为全包名 -->
     <insert id="insertUser" parameterType="com.Gary.bean.User">
         insert into user values(null,#{u_username},#{u_password},#{u_sex},#{u_createTime},#{u_cid})
     </insert>
     
    <!-- 根据id修改username字段的语句 -->
     <update id="updateUser" parameterType="com.Gary.bean.User">
         update user set u_username = #{u_username} where u_id = #{u_id}
     </update>
     
     <!-- 根据id删除用户 -->
     <delete id="deleteUserById" parameterType="Integer">
         delete from user where u_id = #{id}
     </delete>
     
     <!-- 根据UserVo中的User对象的u_id去查询查询用户 -->
     <select id="selectUserByVoId" parameterType="UserVo" resultType="user">
         select * from user where u_id = #{user.u_id}
     </select>
     
     <!-- 查询用户的总条数 -->
     <select id="selectUserCount" resultType="Integer">
         select count(*) from user
     </select>
     
     <!-- 查询所有用户包装类 -->
     <resultMap type="UserVo" id="uservolist">
         <!-- 必须把想要查询数据库的语句都写上 -->
         <id property="u_id" column="u_id"/>
         <id property="u_username" column="u_username"/>
         <id property="u_sex" column="u_sex"/>
         <association property="country" javaType="Country">
             <!-- 必须把想要查询数据库的语句都写上 -->
             <result property="id" column="c_id"/>
             <result property="c_countryname" column="c_countryname"/>
         </association>
     </resultMap>
     
     <select id="selectAllUserVo" resultMap="uservolist">
         SELECT * FROM USER u LEFT JOIN country c ON u.u_cid = c.c_id
     </select>

         
     <select id="selectUserListByUser" parameterType="User" resultType="User">
         <!-- 查询用户性别 模糊用户名 查询用户cid 国际ID -->
         SELECT * FROM user 
             <where>
             <if test="u_sex != null">
                 u_sex = #{u_sex} 
             </if>
             
             <if test="u_username != null">
                 AND u_username like "%"#{u_username}"%"
             </if>
             
             <if test="u_cid != null">
                 AND u_cid = #{u_cid}
             </if>
             </where>
     </select>
     
     
     
</mapper>


 
 

 

 

package com.Gary.test;

import java.io.IOException;
import java.io.InputStream;
import java.util.List;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Test;

import com.Gary.bean.Country;
import com.Gary.bean.CountryVo;
import com.Gary.bean.User;
import com.Gary.bean.UserVo;
import com.Gary.mapper.CountryMapper;
import com.Gary.mapper.UserMapper;

public class MapperTest8 {  

    @Test
    public void Test8() throws IOException {
        //读取配置文件
        String resource = "sqlMapConfig.xml";
                
        InputStream in = Resources.getResourceAsStream(resource);
                
        //创建sqlSessionFactory
        SqlSessionFactory ssf = new SqlSessionFactoryBuilder().build(in);
                
        //生产一个sqlSession
        SqlSession session = ssf.openSession();
                
        UserMapper mapper = session.getMapper(UserMapper.class);
        User u = new User();
        //u.setU_sex("1");
        u.setU_username("王");
        //u.setU_cid(1);
        
        List<User> list = mapper.selectUserListByUser(u);
        
        for(User user : list){
            System.out.println(user);
        }
        
    }
    
}

 

 

3、trim标签 - 定制where标签的规则

　　在<trim>标签中默认使用prefixOverrides去掉前AND，也可以使用suffixOverrides去掉后AND

<select id="selectUserListByUserTrim" parameterType="User" resultType="User">
         <!-- 查询用户性别 模糊用户名 查询用户cid 国际ID -->
         SELECT * FROM user 
             <!-- 默认使用prefixOverrides去掉前AND 也可以使用suffixOverrides去掉后AND -->
             <trim prefix="where" prefixOverrides="">
                 <if test="u_sex != null">
                     u_sex = #{u_sex} 
                 </if>
             
                 <if test="u_username != null">
                     AND u_username like "%"#{u_username}"%"
                 </if>
             
                 <if test="u_cid != null">
                     AND u_cid = #{u_cid}
                 </if>
             </trim>
     </select>

 

<?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.Gary.mapper.UserMapper">
 
     <select id="selectUserById" parameterType="Integer" resultType="user">
         select * from user where u_id = #{id}
     </select>
     
     <!-- #{}占位符 尽量使用#{}来解决问题 -->
     <!-- ${}字符串拼接   容易sql注入 (or 1 = 1) -->
     
     <!-- ${value}中间的字符串一定需要使用value -->
     <select id="selectUserByName" parameterType="String" resultType="com.Gary.bean.User">
         <!-- select * from user where u_username like '%${value}%' -->
              select * from user where u_username like "%"#{name}"%"
     </select>
     
     <!-- 添加用户 参数为全包名 -->
     <insert id="insertUser" parameterType="com.Gary.bean.User">
         insert into user values(null,#{u_username},#{u_password},#{u_sex},#{u_createTime},#{u_cid})
     </insert>
     
    <!-- 根据id修改username字段的语句 -->
     <update id="updateUser" parameterType="com.Gary.bean.User">
         update user set u_username = #{u_username} where u_id = #{u_id}
     </update>
     
     <!-- 根据id删除用户 -->
     <delete id="deleteUserById" parameterType="Integer">
         delete from user where u_id = #{id}
     </delete>
     
     <!-- 根据UserVo中的User对象的u_id去查询查询用户 -->
     <select id="selectUserByVoId" parameterType="UserVo" resultType="user">
         select * from user where u_id = #{user.u_id}
     </select>
     
     <!-- 查询用户的总条数 -->
     <select id="selectUserCount" resultType="Integer">
         select count(*) from user
     </select>
     
     <!-- 查询所有用户包装类 -->
     <resultMap type="UserVo" id="uservolist">
         <!-- 必须把想要查询数据库的语句都写上 -->
         <id property="u_id" column="u_id"/>
         <id property="u_username" column="u_username"/>
         <id property="u_sex" column="u_sex"/>
         <association property="country" javaType="Country">
             <!-- 必须把想要查询数据库的语句都写上 -->
             <result property="id" column="c_id"/>
             <result property="c_countryname" column="c_countryname"/>
         </association>
     </resultMap>
     
     <select id="selectAllUserVo" resultMap="uservolist">
         SELECT * FROM USER u LEFT JOIN country c ON u.u_cid = c.c_id
     </select>

         
     <select id="selectUserListByUser" parameterType="User" resultType="User">
         <!-- 查询用户性别 模糊用户名 查询用户cid 国际ID -->
         SELECT * FROM user 
             <where>
             <if test="u_sex != null">
                 u_sex = #{u_sex} 
             </if>
             
             <if test="u_username != null">
                 AND u_username like "%"#{u_username}"%"
             </if>
             
             <if test="u_cid != null">
                 AND u_cid = #{u_cid}
             </if>
             </where>
     </select>
     
     <select id="selectUserListByUserTrim" parameterType="User" resultType="User">
         <!-- 查询用户性别 模糊用户名 查询用户cid 国际ID -->
         SELECT * FROM user 
             <!-- 默认使用prefixOverrides去掉前AND 也可以使用suffixOverrides去掉后AND -->
             <trim prefix="where" suffixOverrides="AND|OR">
                 <if test="u_sex != null">
                     u_sex = #{u_sex} AND
                 </if>
             
                 <if test="u_username != null">
                     u_username like "%"#{u_username}"%" AND
                 </if>
             
                 <if test="u_cid != null">
                     u_cid = #{u_cid} AND
                 </if>
             </trim>
     </select>
     
</mapper>


 
 

 

 

package com.Gary.test;

import java.io.IOException;
import java.io.InputStream;
import java.util.List;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Test;

import com.Gary.bean.Country;
import com.Gary.bean.CountryVo;
import com.Gary.bean.User;
import com.Gary.bean.UserVo;
import com.Gary.mapper.CountryMapper;
import com.Gary.mapper.UserMapper;

public class MapperTest9 {  

    @Test
    public void Test8() throws IOException {
        //读取配置文件
        String resource = "sqlMapConfig.xml";
                
        InputStream in = Resources.getResourceAsStream(resource);
                
        //创建sqlSessionFactory
        SqlSessionFactory ssf = new SqlSessionFactoryBuilder().build(in);
                
        //生产一个sqlSession
        SqlSession session = ssf.openSession();
                
        UserMapper mapper = session.getMapper(UserMapper.class);
        User u = new User();
        //u.setU_sex("1");
        u.setU_username("王");
        //u.setU_cid(1);
        
        List<User> list = mapper.selectUserListByUserTrim(u);
        
        for(User user : list){
            System.out.println(user);
        }
        
    }
    
}

 

 

4、set标签 - 解决更新数据表时字符串拼接逗号”,”问题；

　　编写一个更新用户updateSetUser的SQL语句

　　<update id="updateSetUser" parameterType="User">
         <!-- 用户名  用户密码 性别 用id来限制 -->
         update user 
         Set
         <if test="u_username != null and u_username != '' ">
             u_username = #{u_username},
         </if>
          <if test="u_password != null and u_password != '' ">
             u_password = #{u_password},
         </if>
          <if test="u_sex != null and u_sex != '' ">
             u_sex = #{u_sex},
         </if>
         
         Where u_id= #{u_id}
         
     </update>

 

 　　发现如果最后一个u_sex条件不成立的时候，会把#{u_password}后边的逗号，遗留下

　　

 

package com.Gary.test;

import java.io.IOException;
import java.io.InputStream;
import java.util.List;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Test;

import com.Gary.bean.Country;
import com.Gary.bean.CountryVo;
import com.Gary.bean.User;
import com.Gary.bean.UserVo;
import com.Gary.mapper.CountryMapper;
import com.Gary.mapper.UserMapper;

public class MapperTest10 {  

    @Test
    public void Test10() throws IOException {
        //读取配置文件
        String resource = "sqlMapConfig.xml";
                
        InputStream in = Resources.getResourceAsStream(resource);
                
        //创建sqlSessionFactory
        SqlSessionFactory ssf = new SqlSessionFactoryBuilder().build(in);
                
        //生产一个sqlSession
        SqlSession session = ssf.openSession();
                
        UserMapper mapper = session.getMapper(UserMapper.class);
        User u = new User();
    
        u.setU_id(1);
        u.setU_username("Gary王");
        u.setU_password("aaa");
        //u.setU_sex("1");    主拼其那两个，会录下一个逗号
        //未提交事务 不会改变数据库
        mapper.updateSetUser(u);
        
        
        
    }
    
}

 

 

5、foreach标签 – 如果需要使用IN查询多条相同数据，可以使用foreach遍历；

　　数据库中使用in标签查询u_id为1，3，5的数据

　　

 

select * from user where u_id in (1,3,5)

 

　　 编写一个使用id更新用户列表selectUserListByIds的SQL语句

<!-- 使用多个id获得用户列表 (1,3,5) -->
     <select id="selectUserListByIds" resultType="User">
         select * 
         from user 
         where u_id 
         in
         <!-- (1，3，5) separator可以组拼逗号 -->
         <foreach collection="array" item="id" open="(" close=")" separator=",">
             #{id}
         </foreach>
     </select>

 

<?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.Gary.mapper.UserMapper">
 
     <select id="selectUserById" parameterType="Integer" resultType="user">
         select * from user where u_id = #{id}
     </select>
     
     <!-- #{}占位符 尽量使用#{}来解决问题 -->
     <!-- ${}字符串拼接   容易sql注入 (or 1 = 1) -->
     
     <!-- ${value}中间的字符串一定需要使用value -->
     <select id="selectUserByName" parameterType="String" resultType="com.Gary.bean.User">
         <!-- select * from user where u_username like '%${value}%' -->
              select * from user where u_username like "%"#{name}"%"
     </select>
     
     <!-- 添加用户 参数为全包名 -->
     <insert id="insertUser" parameterType="com.Gary.bean.User">
         insert into user values(null,#{u_username},#{u_password},#{u_sex},#{u_createTime},#{u_cid})
     </insert>
     
    <!-- 根据id修改username字段的语句 -->
     <update id="updateUser" parameterType="com.Gary.bean.User">
         update user set u_username = #{u_username} where u_id = #{u_id}
     </update>
     
     <!-- 根据id删除用户 -->
     <delete id="deleteUserById" parameterType="Integer">
         delete from user where u_id = #{id}
     </delete>
     
     <!-- 根据UserVo中的User对象的u_id去查询查询用户 -->
     <select id="selectUserByVoId" parameterType="UserVo" resultType="user">
         select * from user where u_id = #{user.u_id}
     </select>
     
     <!-- 查询用户的总条数 -->
     <select id="selectUserCount" resultType="Integer">
         select count(*) from user
     </select>
     
     <!-- 查询所有用户包装类 -->
     <resultMap type="UserVo" id="uservolist">
         <!-- 必须把想要查询数据库的语句都写上 -->
         <id property="u_id" column="u_id"/>
         <id property="u_username" column="u_username"/>
         <id property="u_sex" column="u_sex"/>
         <association property="country" javaType="Country">
             <!-- 必须把想要查询数据库的语句都写上 -->
             <result property="id" column="c_id"/>
             <result property="c_countryname" column="c_countryname"/>
         </association>
     </resultMap>
     
     <select id="selectAllUserVo" resultMap="uservolist">
         SELECT * FROM USER u LEFT JOIN country c ON u.u_cid = c.c_id
     </select>

         
     <select id="selectUserListByUser" parameterType="User" resultType="User">
         <!-- 查询用户性别 模糊用户名 查询用户cid 国际ID -->
         SELECT * FROM user 
             <where>
             <if test="u_sex != null">
                 u_sex = #{u_sex} 
             </if>
             
             <if test="u_username != null">
                 AND u_username like "%"#{u_username}"%"
             </if>
             
             <if test="u_cid != null">
                 AND u_cid = #{u_cid}
             </if>
             </where>
     </select>
     
     <select id="selectUserListByUserTrim" parameterType="User" resultType="User">
         <!-- 查询用户性别 模糊用户名 查询用户cid 国际ID -->
         SELECT * FROM user 
             <!-- 默认使用prefixOverrides去掉前AND 也可以使用suffixOverrides去掉后AND -->
             <trim prefix="where" suffixOverrides="AND|OR">
                 <if test="u_sex != null">
                     u_sex = #{u_sex} AND
                 </if>
             
                 <if test="u_username != null">
                     u_username like "%"#{u_username}"%" AND
                 </if>
             
                 <if test="u_cid != null">
                     u_cid = #{u_cid} AND
                 </if>
             </trim>
     </select>
     
     <update id="updateSetUser" parameterType="User">
         <!-- 用户名  用户密码 性别 用id来限制 -->
         update user 
         <set>
             <if test="u_username != null and u_username != '' ">
                 u_username = #{u_username},
             </if>
              <if test="u_password != null and u_password != '' ">
                 u_password = #{u_password},
             </if>
              <if test="u_sex != null and u_sex != '' ">
                 u_sex = #{u_sex},
             </if>
         </set>
         Where u_id= #{u_id}
         
     </update>
     
     <!-- 使用多个id获得用户列表 (1,3,5) -->
     <select id="selectUserListByIds" resultType="User">
         select * 
         from user 
         where u_id 
         in
         <!-- (1，3，5) separator可以组拼逗号 -->
         <foreach collection="array" item="id" open="(" close=")" separator=",">
             #{id}
         </foreach>
     </select>
     
</mapper>


 
 

 

 

package com.Gary.test;

import java.io.IOException;
import java.io.InputStream;
import java.util.List;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Test;

import com.Gary.bean.Country;
import com.Gary.bean.CountryVo;
import com.Gary.bean.User;
import com.Gary.bean.UserVo;
import com.Gary.mapper.CountryMapper;
import com.Gary.mapper.UserMapper;

public class MapperTest11 {  

    @Test
    public void Test11() throws IOException {
        //读取配置文件
        String resource = "sqlMapConfig.xml";
                
        InputStream in = Resources.getResourceAsStream(resource);
                
        //创建sqlSessionFactory
        SqlSessionFactory ssf = new SqlSessionFactoryBuilder().build(in);
                
        //生产一个sqlSession
        SqlSession session = ssf.openSession();
                
        UserMapper mapper = session.getMapper(UserMapper.class);
        
        Integer[] ids = {1,3,5,7};
        List<User> list = mapper.selectUserListByIds(ids);
        
        for(User user:list) {
            System.out.println(user);
        }
        
        
        
    }
    
}

 

 

6、sql标签 – 可以提取重复sql语句片段；

 　　在Userapper.xml中实现<sql>标签

     <sql id="myselect">
         select * from user
     </sql>

 

 　　之后在UserMapper.xml中可以用<include>把重复引用的sql语句片段加入进去

     <!-- 使用多个id获取用户列表 by userVO -->
     <select id="selectUserListByUserVo" parameterType="UserVo" resultType="User">
         <include refid="myselect"/>
         where u_id 
         in
         <!-- (1，3，5) separator可以组拼逗号 -->
         <foreach collection="idList" item="id" open="(" close=")" separator=",">
             #{id}
         </foreach>
     </select>

 

<?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.Gary.mapper.UserMapper">
 
     <sql id="myselect">
         select * from user
     </sql>
 
     <select id="selectUserById" parameterType="Integer" resultType="user">
         select * from user where u_id = #{id}
     </select>
     
     <!-- #{}占位符 尽量使用#{}来解决问题 -->
     <!-- ${}字符串拼接   容易sql注入 (or 1 = 1) -->
     
     <!-- ${value}中间的字符串一定需要使用value -->
     <select id="selectUserByName" parameterType="String" resultType="com.Gary.bean.User">
         <!-- select * from user where u_username like '%${value}%' -->
              select * from user where u_username like "%"#{name}"%"
     </select>
     
     <!-- 添加用户 参数为全包名 -->
     <insert id="insertUser" parameterType="com.Gary.bean.User">
         insert into user values(null,#{u_username},#{u_password},#{u_sex},#{u_createTime},#{u_cid})
     </insert>
     
    <!-- 根据id修改username字段的语句 -->
     <update id="updateUser" parameterType="com.Gary.bean.User">
         update user set u_username = #{u_username} where u_id = #{u_id}
     </update>
     
     <!-- 根据id删除用户 -->
     <delete id="deleteUserById" parameterType="Integer">
         delete from user where u_id = #{id}
     </delete>
     
     <!-- 根据UserVo中的User对象的u_id去查询查询用户 -->
     <select id="selectUserByVoId" parameterType="UserVo" resultType="user">
         select * from user where u_id = #{user.u_id}
     </select>
     
     <!-- 查询用户的总条数 -->
     <select id="selectUserCount" resultType="Integer">
         select count(*) from user
     </select>
     
     <!-- 查询所有用户包装类 -->
     <resultMap type="UserVo" id="uservolist">
         <!-- 必须把想要查询数据库的语句都写上 -->
         <id property="u_id" column="u_id"/>
         <id property="u_username" column="u_username"/>
         <id property="u_sex" column="u_sex"/>
         <association property="country" javaType="Country">
             <!-- 必须把想要查询数据库的语句都写上 -->
             <result property="id" column="c_id"/>
             <result property="c_countryname" column="c_countryname"/>
         </association>
     </resultMap>
     
     <select id="selectAllUserVo" resultMap="uservolist">
         SELECT * FROM USER u LEFT JOIN country c ON u.u_cid = c.c_id
     </select>

         
     <select id="selectUserListByUser" parameterType="User" resultType="User">
         <!-- 查询用户性别 模糊用户名 查询用户cid 国际ID -->
         SELECT * FROM user 
             <where>
             <if test="u_sex != null">
                 u_sex = #{u_sex} 
             </if>
             
             <if test="u_username != null">
                 AND u_username like "%"#{u_username}"%"
             </if>
             
             <if test="u_cid != null">
                 AND u_cid = #{u_cid}
             </if>
             </where>
     </select>
     
     <select id="selectUserListByUserTrim" parameterType="User" resultType="User">
         <!-- 查询用户性别 模糊用户名 查询用户cid 国际ID -->
         SELECT * FROM user 
             <!-- 默认使用prefixOverrides去掉前AND 也可以使用suffixOverrides去掉后AND -->
             <trim prefix="where" suffixOverrides="AND|OR">
                 <if test="u_sex != null">
                     u_sex = #{u_sex} AND
                 </if>
             
                 <if test="u_username != null">
                     u_username like "%"#{u_username}"%" AND
                 </if>
             
                 <if test="u_cid != null">
                     u_cid = #{u_cid} AND
                 </if>
             </trim>
     </select>
     
     <update id="updateSetUser" parameterType="User">
         <!-- 用户名  用户密码 性别 用id来限制 -->
         update user 
         <set>
             <if test="u_username != null and u_username != '' ">
                 u_username = #{u_username},
             </if>
              <if test="u_password != null and u_password != '' ">
                 u_password = #{u_password},
             </if>
              <if test="u_sex != null and u_sex != '' ">
                 u_sex = #{u_sex},
             </if>
         </set>
         Where u_id= #{u_id}
         
     </update>
     
     <!-- 使用多个id获得用户列表 (1,3,5) -->
     <select id="selectUserListByIds" resultType="User">
         select * 
         from user 
         where u_id 
         in
         <!-- (1，3，5) separator可以组拼逗号 -->
         <foreach collection="array" item="id" open="(" close=")" separator=",">
             #{id}
         </foreach>
     </select>
     
     <!-- 使用多个id获取用户列表 by userVO -->
     <select id="selectUserListByUserVo" parameterType="UserVo" resultType="User">
         <include refid="myselect"/>
         where u_id 
         in
         <!-- (1，3，5) separator可以组拼逗号 -->
         <foreach collection="idList" item="id" open="(" close=")" separator=",">
             #{id}
         </foreach>
     </select>
     
</mapper>


 
 

 

 

package com.Gary.test;

import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.Collection;
import java.util.List;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Test;

import com.Gary.bean.Country;
import com.Gary.bean.CountryVo;
import com.Gary.bean.User;
import com.Gary.bean.UserVo;
import com.Gary.mapper.CountryMapper;
import com.Gary.mapper.UserMapper;

public class MapperTest12 {  

    @Test
    public void Test12() throws IOException {
        //读取配置文件
        String resource = "sqlMapConfig.xml";
                
        InputStream in = Resources.getResourceAsStream(resource);
                
        //创建sqlSessionFactory
        SqlSessionFactory ssf = new SqlSessionFactoryBuilder().build(in);
                
        //生产一个sqlSession
        SqlSession session = ssf.openSession();
        UserMapper mapper = session.getMapper(UserMapper.class);
        
        List<Integer> idList = new ArrayList<Integer>();
        idList.add(1);
        idList.add(4);
        idList.add(8);
        
        UserVo vo = new UserVo();
        vo.setIdList(idList);
        
        List<User> list =mapper.selectUserListByUserVo(vo);
        
        
        
        for(User user:list) {
            System.out.println(user);
        }
        
        
        
    }
    
}