16Mybatis_动态sql_if判断

mybatis的核心就是动态sql.

什么是动态sql:对sql语句进行灵活操作，通过表达式进行判断，对sql进行灵活拼接、组装。

这篇文章讲解sql中的if语句。它可以对查询条件进行判断，如果输入参数不为空才进行查询条件的拼接。这篇文章的核心就是下面的这段代码。

<!-- 
<where></where>相当于sql语句中的where关键字。
这个标签还有一个功能就是自动会去掉第一个and.,比如下面两句sql代码，如果第一个满足的那么就会去掉and这个关键字。

 -->
<where>
        <if test="userCustom!=null">
            <if test="userCustom.sex!=null and userCustom.sex!=''">
                and  user.sex= #{userCustom.sex}
            </if>
            <if  test="userCustom.username!=null and userCustom.username!=''" >

                and user.username=#{userCustom.username}
            </if>

        </if>

    </where>

下面给出u具体案例：

案例代码结构如下：

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" alt="" />

除了userMapper.xml和Mybatis_mappertest.java要修改外，其他的代码都不用变。

userMapper.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">
<!-- nanmespace:命名空间。 作用就是对sql进行分类话管理，理解Sal分离

注意：使用mapper代理方式，namespace有特殊重要的作用
-->

<mapper namespace="cn.itcast.mybatis.mapper.userMapper">

 <!--
 这里的id要和Mapp接口里面的函数名字一模一样。parameterType表示输入的类型，
 resultType表示输出的类型

  -->
    <select id="findUserList" parameterType="cn.itcast.mybatis.po.UserQueryVo" resultType="cn.itcast.mybatis.po.UserCustom">
        SELECT id ,username FROM USER WHERE user.sex= #{userCustom.sex} AND user.username=#{userCustom.username}
    </select>

    <!--
    定义resultMap
    将SELECT id id_,username username_ FROM USER 和User类中的属性做一个映射关系

    type:resultMap最终映射的java对象类型，可以使用别名
    id:对resultMap的唯一标识。
     -->
    <resultMap type="user" id="userResultMap">
        <!--
        id:表示查询结果集中唯一的标识。
        column:查询出来的列名
        property:type指定的pojo类型中的属性名
        最终resultMap对column和property作一个映射关系（对应关系）

         -->
        <id column="id_" property="id"/>
        <result column="username_" property="username"/>
    </resultMap>

        <select id="findUserByResultMap" parameterType="cn.itcast.mybatis.po.UserQueryVo" resultMap="userResultMap">
        SELECT id id_,username username_ FROM USER
    <!-- 

    where可以自动去掉条件中的第一个and
     -->
    <where>
        <if test="userCustom!=null">
            <if test="userCustom.sex!=null and userCustom.sex!=''">
                and  user.sex= #{userCustom.sex}
            </if>
            <if  test="userCustom.username!=null and userCustom.username!=''" >

                and user.username=#{userCustom.username}
            </if>

        </if>

    </where>

    </select>

</mapper>

测试代码Mybatis_mappertest.java代码如下：

package cn.itcast.mybatis.first;

import java.io.IOException;
import java.io.InputStream;
import java.util.Date;
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.Before;
import org.junit.Test;

import cn.itcast.mybatis.mapper.userMapper;
import cn.itcast.mybatis.po.User;
import cn.itcast.mybatis.po.UserCustom;
import cn.itcast.mybatis.po.UserQueryVo;

public class Mybatis_mappertest {

    private SqlSessionFactory sqlSessionFactory;
    @Before
    public void setup() throws IOException
    {   String resource="SqlMapConfig.xml";
        InputStream inputStream= Resources.getResourceAsStream(resource);
        //主要是生成SqlsessionFactory。
        this.sqlSessionFactory=new SqlSessionFactoryBuilder().build(inputStream);
    }
    @Test
    public void testMaper()
    {
        SqlSession sqlSession=null;

        sqlSession=sqlSessionFactory.openSession();
        //生成代理类
        userMapper userMapper=sqlSession.getMapper(userMapper.class);
    //创建包装对象，设置查询条件
        UserQueryVo userQueryVo=new UserQueryVo();
        UserCustom userCustom=new UserCustom();

        // 注意我把这里的sex注销掉了，也就是说sex没有值，那么我们用的是动态的sql语句，就是说sex不会被拼接进去吧
       // userCustom.setSex("1");
        userCustom.setUsername("王王");
        userQueryVo.setUserCustom(userCustom);

        userMapper.findUserByResultMap(userQueryVo);

    }

}

运行如下：

DEBUG [main] - ==>  Preparing: SELECT id id_,username username_ FROM USER WHERE user.username=?

看到没，这里得sql语句中没有 and user.sex= #{userCustom.sex}这条语句。也就是说没有拼接上去。

我们再改一下：干脆把整个userCustom都不输入进去。

结果如下：

DEBUG [main] - ==>  Preparing: SELECT id id_,username username_ FROM USER

看到没，这里的sql语句中什么where后面的语句都没有拼接上去了。