[大数据]MyBatis：动态sql（狂神）

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用where标签替代where 1=1，防止出错

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db.properties：

driver=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/mybatis?useSSL=&useUnicode=true&characterEncoding=utf-8
username=root
password=123456

mybatis-config.xml：

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<!--configuration核心配置文件-->
<configuration>

<!--    引入外部配置文件-->
    <properties resource="db.properties">
        <property name="username" value="root"/>
        <!--默认优先使用外部的db.properties配置文件中的-->
        <property name="password" value="111"/>
    </properties>


<!--    设置日志-->
    <settings>
        <!-- 标准的日志工厂实现：STDOUT_LOGGING控制台输出0-->
        <setting name="logImpl" value="STDOUT_LOGGING"/>
        <!--log4j日志-->
<!--     <setting name="logImpl" value="LOG4J"/>-->
        <!--是否开启自动驼峰命名规则映射-->
        <setting name="mapUnderscoreToCamelCase" value="true"/>
    </settings>


    
<!--    可以给实体类起别名-->
    <typeAliases>
        <typeAlias type="com.kuang.pojo.Blog" alias="blog"/>
    </typeAliases>

    <environments default="development"><!--default：默认的环境这里可以配置：多个环境-->
        <environment id="development">
            <!--事务管理-->
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="${driver}"/>
                <property name="url" value="${url}"/>
                <property name="username" value="${username}"/>
                <property name="password" value="${password}"/>
            </dataSource>
        </environment>
    </environments>

<!-- 映射器   每一个Mapper.xml文件，都需要在Mybatis核心配置文件中注册:指定包下的所有Mapper文件-->
    <mappers>
        <mapper class="com.kuang.dao.BlogMapper"/>
    </mappers>


</configuration>

?Blog：

package com.kuang.pojo;

import lombok.Data;

import java.util.Date;
@Data
public class Blog {
    private String id;
    private String title;
    private String author;
    private Date createTime;//属性名和字段名不一致
    private int views;
}

MybatisUtils：

package com.kuang.utils;

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 java.io.IOException;
import java.io.InputStream;

//sqlSessionFactory --sqlSession
public class MybaitsUtils {
    private static SqlSessionFactory sqlSessionFactory;//提升作用域
    /*
    所谓的代码块就是一段独立的代码空间，那什么是静态代码块呢？说白了，静态代码块就是用static修饰的代码块，关于静态代码块的概念不多说，不过你需要知道它的一个特点，那就是

   随着类的加载而执行，而且只执行一次
     */
    static{
        try {
            //使用MyBaits获取sqlSessionFactory对象
            String resource = "mybatis-config.xml";
            InputStream inputStream = Resources.getResourceAsStream(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        }catch(IOException e){
            e.printStackTrace();
        }
    }
    //既然有了 SqlSessionFactory，顾名思义，我们可以从中获得 SqlSession 的实例。
    // SqlSession 提供了在数据库执行 SQL 命令所需的所有方法。
    public static SqlSession getSqlSession(){
        //获取SqlSession对象
         SqlSession sqlSession=sqlSessionFactory.openSession(true);//true设置事务自动提交，执行增删改，sql不用手动提交
         return sqlSession;
    }
}

IDUtils：生成id

package com.kuang.utils;

import org.junit.Test;

import java.util.UUID;

public class IDUtils {
    public static String getId(){
        return UUID.randomUUID().toString().replaceAll("-","");
    }
    @Test
    public void test(){
        System.out.println(IDUtils.getId());
        System.out.println(IDUtils.getId());
        System.out.println(IDUtils.getId());
    }
}

BlogMapper:

package com.kuang.dao;

import com.kuang.pojo.Blog;

import java.util.List;
import java.util.Map;

public interface BlogMapper {
    //插入数据
    int addBlog(Blog blog);

    //查询博客
    List<Blog> queryBlogIF(Map map);
}

BlogMapper.xml:动态sql if标签
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<?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.kuang.dao.BlogMapper">
    <!--使用insert，update，delete，select标签来写sql语句-->

    <insert id="addBlog" parameterType="blog">

        insert into mybatis.blog (id, title, author, create_time, views)
        values (#{id},#{title},#{author},#{createTime},#{views});

    </insert>

    <select id="queryBlogIF" parameterType="map" resultType="blog">
        select * from mybatis.blog where 1=1
        <if test="title !=null">
            and title =#{title}
        </if>
        <if test="author!=null">
            and author =#{author}
        </if>
    </select>

</mapper>

MyTest:

import com.kuang.dao.BlogMapper;
import com.kuang.pojo.Blog;
import com.kuang.utils.IDUtils;
import com.kuang.utils.MybaitsUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

import java.util.Date;
import java.util.HashMap;
import java.util.List;


public class MyTest {
    @Test
    public void addBlogTest(){
        SqlSession sqlSession = MybaitsUtils.getSqlSession();
        BlogMapper mapper = sqlSession.getMapper(BlogMapper.class);

        Blog blog = new Blog();
        blog.setId(IDUtils.getId());
        blog.setTitle("Mybatis如此简单");
        blog.setAuthor("狂神说");
        blog.setCreateTime(new Date());
        blog.setViews(9999);

        mapper.addBlog(blog);

        blog.setId(IDUtils.getId());
        blog.setTitle("Java如此简单");
        mapper.addBlog(blog);

        blog.setId(IDUtils.getId());
        blog.setTitle("Spring");
        mapper.addBlog(blog);

        blog.setId(IDUtils.getId());
        blog.setTitle("微服务如此简单");
        mapper.addBlog(blog);

        sqlSession.close();
    }

    @Test
    public void queryBlogIF(){
        SqlSession sqlSession=MybaitsUtils.getSqlSession();
        BlogMapper mapper=sqlSession.getMapper(BlogMapper.class);

        HashMap map=new HashMap();
       // map.put("author","狂神说");
       map.put("title","Java如此简单");
        List<Blog> blogs = mapper.queryBlogIF(map);
        for (Blog blog : blogs) {
            System.out.println(blog);
        }
        sqlSession.close();
    }
}

运行addTestBlogTest：往表中插入数据

queryBlogIF：

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切换map注释：

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?BlogMapper：

package com.kuang.dao;

import com.kuang.pojo.Blog;

import java.util.List;
import java.util.Map;

public interface BlogMapper {
    //插入数据
    int addBlog(Blog blog);

    //查询博客
    List<Blog> queryBlogIF(Map map);

    //
    List<Blog> queryBlogChoose(Map map);

    //更新博客
    int UpdateBlog(Map map);

    //查询第1-3号记录的博客
    List<Blog> queryBlogForeach(Map map);
}

BlogMapper.xml:动态sql常用标签

<?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.kuang.dao.BlogMapper">
    <!--使用insert，update，delete，select标签来写sql语句-->

    <insert id="addBlog" parameterType="blog">
        insert into mybatis.blog (id, title, author, create_time, views)
        values (#{id},#{title},#{author},#{createTime},#{views});
    </insert>

    <!--<select id="queryBlogIF" parameterType="map" resultType="blog">
        select * from mybatis.blog where 1=1
        <if test="title !=null">
            and title =#{title}
        </if>
        <if test="author!=null">
            and author =#{author}
        </if>
    </select>-->
<!-- where标签优化上面   如果输入的条件第一个不满足，它会自动把and去掉-->
    <select id="queryBlogIF" parameterType="map" resultType="blog">
        select * from mybatis.blog
        <where>
        <if test="title !=null">
            title =#{title}
        </if>
        <if test="author!=null">
            and author =#{author}
        </if>
        </where>
    </select>

<!--    如果输入的条件都满足，他只会让第一个生效，第一个不满足，会把第二个的and去掉-->
    <select id="queryBlogChoose" parameterType="map" resultType="blog">
        select * from mybatis.blog
        <where>
           <choose>
            <when test="title !=null">
                 title =#{title}
            </when>
            <when test="author!=null">
                and author =#{author}
            </when>
            <otherwise>
                and views=#{views}
            </otherwise>
           </choose>
        </where>
    </select>

    <update id="UpdateBlog" parameterType="map">
        update mybatis.blog
        <set>
            <if test="title!=null">
                title=#{title},
            </if>
            <if test="author!=null">
                author=#{author}
            </if>
        </set>
        where id=#{id}
    </update>

</mapper>

MyTest:

import com.kuang.dao.BlogMapper;
import com.kuang.pojo.Blog;
import com.kuang.utils.IDUtils;
import com.kuang.utils.MybaitsUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

import java.util.ArrayList;
import java.util.Date;
import java.util.HashMap;
import java.util.List;


public class MyTest {
    //插入数据
    @Test
    public void addBlogTest(){
        SqlSession sqlSession = MybaitsUtils.getSqlSession();
        BlogMapper mapper = sqlSession.getMapper(BlogMapper.class);

        Blog blog = new Blog();
        blog.setId(IDUtils.getId());
        blog.setTitle("Mybatis如此简单");
        blog.setAuthor("狂神说");
        blog.setCreateTime(new Date());
        blog.setViews(9999);

        mapper.addBlog(blog);

        blog.setId(IDUtils.getId());
        blog.setTitle("Java如此简单");
        mapper.addBlog(blog);

        blog.setId(IDUtils.getId());
        blog.setTitle("Spring");
        mapper.addBlog(blog);

        blog.setId(IDUtils.getId());
        blog.setTitle("微服务如此简单");
        mapper.addBlog(blog);

        sqlSession.close();
    }

    //where标签查询
    @Test
    public void queryBlogIF(){
        SqlSession sqlSession=MybaitsUtils.getSqlSession();
        BlogMapper mapper=sqlSession.getMapper(BlogMapper.class);

        HashMap map=new HashMap();
        map.put("author","狂神说");
        //map.put("title","Java如此简单");
        List<Blog> blogs = mapper.queryBlogIF(map);
        for (Blog blog : blogs) {
            System.out.println(blog);
        }
        sqlSession.close();
    }
    //Choose查询，相当于switch它会找满足条件的一个
    @Test
    public void queryBlogChoose(){
        SqlSession sqlSession=MybaitsUtils.getSqlSession();
        BlogMapper mapper=sqlSession.getMapper(BlogMapper.class);

        HashMap map=new HashMap();
        map.put("title","Java如此简单");
        map.put("author","狂神说");
        map.put("views",9999);

        List<Blog> blogs = mapper.queryBlogChoose(map);
        for (Blog blog : blogs) {
            System.out.println(blog);
        }
        sqlSession.close();
    }

    //Set更新
    @Test
    public void UpdateBlog(){
        SqlSession sqlSession=MybaitsUtils.getSqlSession();
        BlogMapper mapper=sqlSession.getMapper(BlogMapper.class);

        HashMap map=new HashMap();
        map.put("author","狂神说1");
        map.put("title","Java如此简单");
        map.put("id","311ace05e43747b49db2cc2ff61b687e");

        int i = mapper.UpdateBlog(map);
        if (i>0){
            System.out.println("更新成功");
        }

        sqlSession.close();
    }
    //查询第1-3号记录的博客
    @Test
    public void queryBlogForeach(){
        SqlSession sqlSession=MybaitsUtils.getSqlSession();
        BlogMapper mapper=sqlSession.getMapper(BlogMapper.class);

        HashMap map=new HashMap();

        ArrayList<Integer> ids=new ArrayList<Integer>();
        ids.add(1);
        ids.add(2);
        ids.add(3);

        map.put("ids",ids);
        List<Blog> blogs = mapper.queryBlogForeach(map);
        for (Blog blog : blogs) {
            System.out.println(blog);
        }

        sqlSession.close();
    }
}

queryBlogIF?

?queryBlogChoose:

choose相当于switch只会在查找满足条件的一个，如果把注释的内容打开，只会第一个条件生效??

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UpdateBlog：

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?BlogMapper.xml:

<?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.kuang.dao.BlogMapper">
    <!--使用insert，update，delete，select标签来写sql语句-->

    <insert id="addBlog" parameterType="blog">
        insert into mybatis.blog (id, title, author, create_time, views)
        values (#{id},#{title},#{author},#{createTime},#{views});
    </insert>

    <!--<select id="queryBlogIF" parameterType="map" resultType="blog">
        select * from mybatis.blog where 1=1
        <if test="title !=null">
            and title =#{title}
        </if>
        <if test="author!=null">
            and author =#{author}
        </if>
    </select>-->

<!--    代码片段-->
    <sql id="if-title-author">
        <if test="title !=null">
            title =#{title}
        </if>
        <if test="author!=null">
            and author =#{author}
        </if>
    </sql>

<!--where标签优化    如果输入的条件第一个不满足，它会自动把and去掉
利用代码片段：
        <include refid="if-title-author"></include>
-->
    <select id="queryBlogIF" parameterType="map" resultType="blog">
        select * from mybatis.blog
        <where>
          <include refid="if-title-author"></include>
        </where>
    </select>

<!--    如果输入的条件都满足，他只会让第一个生效，第一个不满足，会把第二个的and去掉-->
    <select id="queryBlogChoose" parameterType="map" resultType="blog">
        select * from mybatis.blog
        <where>
           <choose>
            <when test="title !=null">
                 title =#{title}
            </when>
            <when test="author!=null">
                and author =#{author}
            </when>
            <otherwise>
                and views=#{views}
            </otherwise>
           </choose>
        </where>
    </select>

    <update id="UpdateBlog" parameterType="map">
        update mybatis.blog
        <set>
            <if test="title!=null">
                title=#{title},
            </if>
            <if test="author!=null">
                author=#{author}
            </if>
        </set>
        where id=#{id}
    </update>


<!--    select * from mybatis.blog where 1=1 and (id=1 or id=2 or id=3)
       我们现在传递一个万能的map，这个map中可以存在一个集合！
-->
    <select id="queryBlogForeach" parameterType="map" resultType="blog">
        select * from mybatis.blog
        <where>
            <foreach collection="ids" item="id" open="and (" close=")" separator="or">
                id=#{id}
            </foreach>
        </where>
    </select>

</mapper>

queryBlogForeach：

当不忘List集合中添加id

/*ids.add(1);
ids.add(2);
ids.add(3);*/

?去掉注释：

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