Mybatis 动态SQL插入操作②

?结合上个博客一起看哦

上篇博客我们说.用户在表中插入数据的时候,有的数据可能不想插入,我们就需要设置,当用户插入这个字段的数据的时候就显示,不插入的话就为null,比如性别不想插入,那么 XML 代码如下

<?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.mybatisdemo.mapper.UserInfo2Mapper">
    <insert id="insertByXML">
        insert into userinfo(username,password,age,
        <if test="gender!=null">
            gender,
        </if>
        phone)
        values(#{username},#{password},#{age},
        <if test="gender!=null">
            #{gender},
        </if>
        #{phone})
    </insert>
</mapper>

那如果每个字段都像性别那样设置,代码该如何去写呢,以此类推大概是下面这样的写法

<?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.mybatisdemo.mapper.UserInfo2Mapper">
    <insert id="insertByXML">
        insert into userinfo(
        <if test="username!=null">
            username,
        </if>
        <if test="password!=null">
            password,
        </if>
        <if test="username!=null">
            age,
        </if>
        <if test="gender!=null">
            gender,
        </if>
        <if test="phone!=null">
            phone
        </if>
        )
        values(
        <if test="username!=null">
            #{username},
        </if>
        <if test="password!=null">
            #{password},
        </if>
        <if test="age!=null">
            #{age},
        </if>
        <if test="gender!=null">
            #{gender},
        </if>
        <if test="phone!=null">
            #{phone}
        </if>
        )
    </insert>
</mapper>

?按理来说是上面这样写,但是插入数据的时候,假如有两个字段没插入数据,那就会因为逗号的问题报错.比如 gender 和 phone 都没插入数据,那么 age 就成了最后的数据,age 后面跟着逗号就不行

具体错误的日志我这里就不展示了,接下来我们说怎么解决逗号的问题

所以我们需要引入 trim标签 帮我们解决逗号问题

把 trim 标签给加上?,我们把括号也交给 trim 处理

<?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.mybatisdemo.mapper.UserInfo2Mapper">
    <insert id="insertByXML">
        insert into userinfo
        <trim suffixOverrides="," prefix="(" suffix=")">
            <if test="username!=null">
                username,
            </if>
            <if test="password!=null">
                password,
            </if>
            <if test="age!=null">
                age,
            </if>
            <if test="gender!=null">
                gender,
            </if>
            <if test="phone!=null">
                phone
            </if>
        </trim>
        values(
        <trim suffixOverrides=",">
            <if test="username!=null">
                #{username},
            </if>
            <if test="password!=null">
                #{password},
            </if>
            <if test="age!=null">
                #{age},
            </if>
            <if test="gender!=null">
                #{gender},
            </if>
            <if test="phone!=null">
                #{phone}
            </if>
        </trim>
        )
    </insert>
</mapper>

?然后我们试试只添加三个字段的数据

package com.example.mybatisdemo.mapper;

import com.example.mybatisdemo.model.UserInfo;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;

import static org.junit.jupiter.api.Assertions.*;

@SpringBootTest
class UserInfo2MapperTest {
    @Autowired
    private UserInfo2Mapper userInfo2Mapper;
   
    @Test
    void insertByXML() {
        UserInfo userInfo = new UserInfo();
        userInfo.setUsername("ppp");
        userInfo.setPassword("555www");
        userInfo.setAge(23);
        //userInfo.setGender(1);
        //userInfo.setPhone("177966");
        userInfo2Mapper.insertByXML(userInfo);
    }
}

?没问题