时间:2021-07-01 10:21:17 帮助过:18人阅读
耳中所听恍若你呢喃,心之所向是指你为南,目之所及除你之外尽是荒野。
什么是动态SQL:
? 动态SQL就是根据不同的条件生成不同的SQL语句
建表
- <code>CREATE TABLE `bolg`(
- `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',
- `creat_time` datetime not null comment '创建时间',
- `views` int(30) not null comment '浏览量'
- )ENGINE=InnoDB DEFAULT CHARSET=utf8</code>
创建一个基础工程
导包
编写配置文件
编写实体类
- <code>@Data
- public class Blog {
- private int id;
- private String title;
- private String author;
- private Date creatTime;
- private int views;
- }</code>
编写实体类对应的Mapper接口和Mapper.xm
- <code><select id="queryBlogIF" parameterType="map" resultType="com.rui.pojo.Blog">
- select * from mybatis.bolg where 1=1
- <if test="title != null">
- and title = #{title}
- </if>
- <if test="author != null">
- and author = #{author}
- </if>
- </select></code>
- <code>@Test
- public void queryBlogIF(){
- SqlSession sqlSession = MyBatisUtils.getSqlSession();
- BlogMapper mapper = sqlSession.getMapper(BlogMapper.class);
- HashMap map = new HashMap();
- map.put("author","尹锐");
- List<Blog> blogs = mapper.queryBlogIF(map);
- for (Blog blog : blogs) {
- System.out.println(blog);
- }
- sqlSession.close();
- }</code>
- <code><select id="queryBlogChoose" parameterType="map" resultType="com.rui.pojo.Blog">
- select * from mybatis.bolg
- <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></code>
- <code>select * from mybatis.bolg
- <where>
- <if test="title != null">
- title = #{title}
- </if>
- <if test="author != null">
- and author = #{author}
- </if>
- </where></code>
- <code><update id="updateBlog" parameterType="map">
- update mybatis.bolg
- <set>
- <if test="title != null">
- title = #{title},
- </if>
- <if test="author != null">
- author = #{author},
- </if>
- </set>
- where id = #{id}
- </update></code>
所谓的动态SQL,本质还是SQL语句,只是我们可以在SQL层面,去执行一些逻辑代码
- <code>select * from user where 1=1 and
- <foreach item="id" index="index" collection="ids"
- open="(" separator="or" close=")">
- #{id}
- </foreach>
- (id=1 or id=2 or id=3)</code>
- <code><!--
- select * from mybatis.bolg 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map
- -->
- <select id="queryBlogForeach" parameterType="map" resultType="com.rui.pojo.Blog">
- select * from mybatis.bolg
- <where>
- <foreach collection="ids" item="id" open="(" close=")" separator="or">
- id = #{id}
- </foreach>
- </where>
- </select></code>
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:
有的时候,我们可能会将一些公共的部分抽取处理,方便复用
使用SQL标签抽取公共的部分
- <code><sql id="if-title-author">
- <if test="title != null">
- title = #{title}
- </if>
- <if test="author != null">
- and author = #{author}
- </if>
- </sql></code>
在需要使用的地方使用Include
标签引用即可
- <code><select id="queryBlogIF" parameterType="map" resultType="com.rui.pojo.Blog">
- select * from mybatis.bolg
- <where>
- <include refid="if-title-author"></include>
- </where>
- </select></code>
注意事项:
MyBatis——动态SQL
标签:ash sep hash ati 基于 时间 ids 语句 配置