Mybatis 動態查詢 -- if、choose(when、otherwise)、trim(where、set)、foreach
阿新 • • 發佈:2021-01-27
前文
- 此博文參考 Mybatis 中文官方文件:https://mybatis.org/mybatis-3/zh/dynamic-sql.html
- 原始碼(親測,可直接執行):https://github.com/KUANG-CHENG/Spring(mybatis-sql)
- 編寫不易,如果對您有幫助,請點個贊,謝謝!
- 編譯環境:IDEA 2020、 MySQL 8.0、Maven 3.6.3
文章目錄
- 一、環境搭建
- 二、動態SQL -- if 語句
- 三、動態SQL -- choose(when、otherwise)語句
- 四、動態SQL -- trim(where、set)語句
- 五、動態SQL -- foreach 語句
- 六、小結
一、環境搭建
1.1 建立資料表 Blog
- 建立5個欄位 id、title、author、create_time、views
CREATE TABLE `blog` (
`id` varchar (50) NOT NULL COMMENT '部落格id',
`title` varchar(100) NOT NULL COMMENT '部落格標題',
`author` varchar(30) NOT NULL COMMENT '部落格作者',
`create_time` datetime NOT NULL COMMENT '建立時間',
`views` int(30) NOT NULL COMMENT '瀏覽量'
) ENGINE=InnoDB DEFAULT CHARSET=utf8
- 新增資料
1.2 建立基本 Maven 工程
-
工程目錄如下:
-
利用 Maven 匯入 jar 包
<!--匯入依賴-->
<dependencies>
<!--mysql驅動-->
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>5.1.47</version>
</dependency>
<!--mybatis-->
<!-- https://mvnrepository.com/artifact/org.mybatis/mybatis -->
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>3.5.2</version>
</dependency>
<!--junit-->
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.12</version>
</dependency>
<!--LOG4J-->
<dependency>
<groupId>log4j</groupId>
<artifactId>log4j</artifactId>
<version>1.2.17</version>
</dependency>
<!-- lombok -->
<dependency>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
<version>1.18.12</version>
</dependency>
</dependencies>
- 編寫 mybatis-config.xml 配置檔案
<?xml version="1.0" encoding="UTF8" ?>
<!DOCTYPE configuration
PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<!--configuration核心配置檔案-->
<configuration>
<!-- properties檔案匯入引數 -->
<properties resource="db.properties">
<property name="pwd" value="Kc635908933"/>
</properties>
<settings>
<!-- 標準日誌實現 -->
<!-- <setting name="logImpl" value="STDOUT_LOGGING"/> -->
<!-- 駝峰命名 -->
<setting name="mapUnderscoreToCamelCase" value="true"/>
</settings>
<!-- 類型別名 -->
<typeAliases>
<!-- <typeAlias type="com.pojo.User" alias="User"/> -->
<package name="com.pojo"/>
</typeAliases>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<property name="driver" value="${driver}"/>
<property name="url" value="${url}"/>
<property name="username" value="${username}"/>
<property name="password" value="${pwd}"/>
</dataSource>
</environment>
</environments>
<mappers>
<mapper class="com.dao.BlogMapper"></mapper>
</mappers>
</configuration>
- 編寫 Blog.class 實體類
@Data
public class Blog {
private String id;
private String title;
private String author;
private Date create_time;
private int views;
}
- 編寫實體類對應 BlogMapper介面 和 BlogMapper.xml檔案
BlogMapper介面
public interface BlogMapper {
// 插入資料
int addBlog(Blog blog);
}
BlogMapper.xml
<?xml version="1.0" encoding="UTF8" ?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.dao.BlogMapper">
<!-- 插入部落格-->
<insert id="addBlog" parameterType="blog">
insert into mybatis.blog(id, title, author, create_time, views)
values (#{id},#{title},#{author},#{create_time},#{views})
</insert>
</mapper>
1.3 插入資料測試程式碼
@Test
public void addInitBlog(){
SqlSession session = MybatisUtils.getSqlSession();
BlogMapper mapper = session.getMapper(BlogMapper.class);
Blog blog = new Blog();
blog.setId(IDUtils.getId());
blog.setTitle("Mybatis如此簡單");
blog.setAuthor("kc");
blog.setCreate_time(new Date());
blog.setViews(9999);
mapper.addBlog(blog);
blog.setId(IDUtils.getId());
blog.setTitle("Java如此簡單");
mapper.addBlog(blog);
blog.setId(IDUtils.getId());
blog.setTitle("Spring如此簡單");
mapper.addBlog(blog);
blog.setId(IDUtils.getId());
blog.setTitle("微服務如此簡單");
mapper.addBlog(blog);
session.close();
}
二、動態SQL – if 語句
2.1 BlogMapper.xml 介面實現
// 查詢部落格
List<Blog> queryBlogIF(Map map);
<!-- sql語句片段 -->
<sql id="select-title-author">
<if test=" title != null">
and title = #{title}
</if>
<if test=" author != null">
and auther = #{auther}
</if>
</sql>
<!-- 動態查詢if -->
<select id="queryBlogIF" parameterType="Map" resultType="Blog">
select * from mybatis.blog
<where>
<include refid="select-title-author"></include>
</where>
</select>
2.2 測試函式
@Test
public void queryBlogIF(){
SqlSession session = MybatisUtils.getSqlSession();
BlogMapper mapper = session.getMapper(BlogMapper.class);
Map map = new HashMap();
map.put("title", "Java如此簡單3");
List<Blog> blogs = mapper.queryBlogIF(map);
for (Blog blog : blogs) {
System.out.println(blog);
}
session.close();
}
三、動態SQL – choose(when、otherwise)語句
3.1 BlogMapper.xml 介面實現
// 查詢部落格 Choose
List<Blog> queryBlogChoose(Map map);
<!-- 動態查詢 choose -->
<select id="queryBlogChoose" parameterType="Map" resultType="Blog">
select * from mybatis.blog
<where>
<choose>
<when test="title != null">
title = #{title}
</when>
<when test="auther != null">
auther = #{auther}
</when>
<otherwise>
1 = 1
</otherwise>
</choose>
</where>
</select>
3.2 測試函式
@Test
public void queryBlogChoose(){
SqlSession session = MybatisUtils.getSqlSession();
BlogMapper mapper = session.getMapper(BlogMapper.class);
Map map = new HashMap();
map.put("title", "Java如此簡單");
List<Blog> blogs = mapper.queryBlogChoose(map);
for (Blog blog : blogs) {
System.out.println(blog);
}
session.close();
}
四、動態SQL – trim(where、set)語句
4.1 BlogMapper.xml 介面實現
// 更新部落格 Set
int updateBlog(Map map);
<!-- 更新 set -->
<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>
4.2 測試函式
@Test
public void updateBlog(){
SqlSession session = MybatisUtils.getSqlSession();
BlogMapper mapper = session.getMapper(BlogMapper.class);
Map map = new HashMap();
map.put("title", "Java如此簡單3");
map.put("author","kuangcheng2");
map.put("id","2");
int num = mapper.updateBlog(map);
System.out.println(num);
session.close();
}
4.3 trim 函式
- 覆蓋前面的值
<trim prefix="WHERE" prefixOverrides="AND |OR ">
...
</trim>
- 覆蓋後面的值
<trim prefix="SET" suffixOverrides=",">
...
</trim>
五、動態SQL – foreach 語句
5.1 BlogMapper.xml 介面實現
// 查詢 foreach -- 1、2、3
List<Blog> queryBlogForeach(Map map);
<!-- 動態查詢 foreach -->
<!-- select * from mybatis.blog where 1=1 and (id=1 or id=2 or id=3) -->
<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>
5.2 測試函式
@Test
public void queryBlogForeach(){
SqlSession session = MybatisUtils.getSqlSession();
BlogMapper mapper = session.getMapper(BlogMapper.class);
Map map = new HashMap();
ArrayList<Integer> ids = new ArrayList<Integer>();
ids.add(1);
ids.add(2);
map.put("ids", ids);
List<Blog> blogs = mapper.queryBlogForeach(map);
for (Blog blog : blogs) {
System.out.println(blog);
}
session.close();
}
六、小結
所謂的動態SQL,本質還是SQL語句 , 只是我們可以在SQL層面,去執行一個邏輯程式碼
動態SQL就是在拼接SQL語句,我們只要保證SQL的正確性,按照SQL的格式,去排列組合就可以了
建議:
現在Mysql中寫出完整的SQL,再對應的去修改成為我們的動態SQL實現通用即可!