前文
- 此博文参考 Mybatis 中文官方文档：https://mybatis.org/mybatis-3/zh/dynamic-sql.html
- 源代码（亲测，可直接运行）：https://github.com/KUANG-CHENG/Spring（mybatis-sql）
- 编写不易，如果对您有帮助，请点个赞，谢谢！
- 编译环境：IDEA 2020、 MySQL 8.0、Maven 3.6.3
文章目录
一、环境搭建
1.1 创建数据表 Blog
- 创建5个字段 id、title、author、create_time、views
CREATE TABLE `blog` (
`id` varchar(50) NOT NULL COMMENT '博客id',
`title` varchar(100) NOT NULL COMMENT '博客标题',
`author` varchar(30) NOT NULL COMMENT '博客作者',
`create_time` datetime NOT NULL COMMENT '创建时间',
`views` int(30) NOT NULL COMMENT '浏览量'
) ENGINE=InnoDB DEFAULT CHARSET=utf8
- 添加数据
1.2 创建基本 Maven 工程
-
工程目录如下：
-
利用 Maven 导入 jar 包
<!--导入依赖-->
<dependencies>
<!--mysql驱动-->
<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>
- 编写 mybatis-config.xml 配置文件
<?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核心配置文件-->
<configuration>
<!-- properties文件导入参数 -->
<properties resource="db.properties">
<property name="pwd" value="Kc635908933"/>
</properties>
<settings>
<!-- 标准日志实现 -->
<!-- <setting name="logImpl" value="STDOUT_LOGGING"/> -->
<!-- 驼峰命名 -->
<setting name="mapUnderscoreToCamelCase" value="true"/>
</settings>
<!-- 类型别名 -->
<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>
- 编写 Blog.class 实体类
@Data
public class Blog {
private String id;
private String title;
private String author;
private Date create_time;
private int views;
}
- 编写实体类对应 BlogMapper接口 和 BlogMapper.xml文件
BlogMapper接口
public interface BlogMapper {
// 插入数据
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">
<!-- 插入博客-->
<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 插入数据测试代码
@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如此简单");
blog.setAuthor("kc");
blog.setCreate_time(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如此简单");
mapper.addBlog(blog);
blog.setId(IDUtils.getId());
blog.setTitle("微服务如此简单");
mapper.addBlog(blog);
session.close();
}
二、动态SQL – if 语句
2.1 BlogMapper.xml 接口实现
// 查询博客
List<Blog> queryBlogIF(Map map);
<!-- sql语句片段 -->
<sql id="select-title-author">
<if test=" title != null">
and title = #{title}
</if>
<if test=" author != null">
and auther = #{auther}
</if>
</sql>
<!-- 动态查询if -->
<select id="queryBlogIF" parameterType="Map" resultType="Blog">
select * from mybatis.blog
<where>
<include refid="select-title-author"></include>
</where>
</select>
2.2 测试函数
@Test
public void queryBlogIF(){
SqlSession session = MybatisUtils.getSqlSession();
BlogMapper mapper = session.getMapper(BlogMapper.class);
Map map = new HashMap();
map.put("title", "Java如此简单3");
List<Blog> blogs = mapper.queryBlogIF(map);
for (Blog blog : blogs) {
System.out.println(blog);
}
session.close();
}
三、动态SQL – choose（when、otherwise）语句
3.1 BlogMapper.xml 接口实现
// 查询博客 Choose
List<Blog> queryBlogChoose(Map map);
<!-- 动态查询 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 测试函数
@Test
public void queryBlogChoose(){
SqlSession session = MybatisUtils.getSqlSession();
BlogMapper mapper = session.getMapper(BlogMapper.class);
Map map = new HashMap();
map.put("title", "Java如此简单");
List<Blog> blogs = mapper.queryBlogChoose(map);
for (Blog blog : blogs) {
System.out.println(blog);
}
session.close();
}
四、动态SQL – trim（where、set）语句
4.1 BlogMapper.xml 接口实现
// 更新博客 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 测试函数
@Test
public void updateBlog(){
SqlSession session = MybatisUtils.getSqlSession();
BlogMapper mapper = session.getMapper(BlogMapper.class);
Map map = new HashMap();
map.put("title", "Java如此简单3");
map.put("author","kuangcheng2");
map.put("id","2");
int num = mapper.updateBlog(map);
System.out.println(num);
session.close();
}
4.3 trim 函数
- 覆盖前面的值
<trim prefix="WHERE" prefixOverrides="AND |OR ">
...
</trim>
- 覆盖后面的值
<trim prefix="SET" suffixOverrides=",">
...
</trim>
五、动态SQL – foreach 语句
5.1 BlogMapper.xml 接口实现
// 查询 foreach -- 1、2、3
List<Blog> queryBlogForeach(Map map);
<!-- 动态查询 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 测试函数
@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、小结
所谓的动态SQL，本质还是SQL语句 ， 只是我们可以在SQL层面，去执行一个逻辑代码
动态SQL就是在拼接SQL语句，我们只要保证SQL的正确性，按照SQL的格式，去排列组合就可以了
建议：
现在Mysql中写出完整的SQL,再对应的去修改成为我们的动态SQL实现通用即可！