mybatis知识点总结02

1 动态SQL
1.1 什么是动态SQL？动态SQL的作用
动态SQL指的是根据不同的查询条件 , 生成不同的Sql语句。通过 if, choose, when, otherwise, trim, where, set, foreach等标签，可组合成非常灵活的SQL语句，从而在提高 SQL 语句的准确性的同时，也大大提高了开发人员的效率。

1.2 搭建环境

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

1.3 编写代码

import java.util.Date;

public class Blog {

private String id;
private String title;
private String author;
private Date createTime;
private int views;
//set，get....
}
public interface BlogMapper {//需求1:根据作者名字和博客名字来查询博客！如果作者名字为空，那么只根据博客名字查询，反之，则根据作者名来查询
List<Blog> queryBlogIf(Map map);
// 需求2：我们需要查询 blog 表中 id 分别为1,2,3的博客信息
List<Blog> queryBlogForeach(Map map);
}
<select id="queryBlogIf" parameterType="map" resultType="blog">
select * from blog
<where>
<if test="title != null">
title = #{title}
</if>
<if test="author != null">
and author = #{author}
</if>
</where>
</select>
<!--注意set是用的逗号隔开-->
<update id="updateBlog" parameterType="map">
update blog
<set>
<if test="title != null">
title = #{title},
</if>
<if test="author != null">
author = #{author}
</if>
</set>
where id = #{id};
</update>
<select id="queryBlogChoose" parameterType="map" resultType="blog">
select * from 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>
<select id="queryBlogForeach" parameterType="map" resultType="blog">
select * from blog
<where>
<!--
collection:指定输入对象中的集合属性
item:每次遍历生成的对象
open:开始遍历时的拼接字符串
close:结束时拼接的字符串
separator:遍历对象之间需要拼接的字符串
select * from blog where 1=1 and (id=1 or id=2 or id=3)
-->
<foreach collection="ids" item="id" open="and (" close=")" separator="or">
id=#{id}
</foreach>
</where>
</select>
List<Blog> queryBlogChoose(Map map);
int updateBlog(Map map);
@Test
public void testQueryBlogIf(){
SqlSession session = MybatisUtils.getSession();
BlogMapper mapper = session.getMapper(BlogMapper.class);

HashMap<String, String> map = new HashMap<String, String>();
map.put("title","Mybatis如此简单");
map.put("author","狂神说");
List<Blog> blogs = mapper.queryBlogIf(map);

System.out.println(blogs);

session.close();
}

@Test
public void testUpdateBlog(){
SqlSession session = MybatisUtils.getSession();
BlogMapper mapper = session.getMapper(BlogMapper.class);

HashMap<String, String> map = new HashMap<String, String>();
map.put("title","动态SQL");
map.put("author","秦疆");
map.put("id","9d6a763f5e1347cebda43e2a32687a77");

mapper.updateBlog(map);


session.close();
}

@Test
public void testQueryBlogChoose(){
SqlSession session = MybatisUtils.getSession();
BlogMapper mapper = session.getMapper(BlogMapper.class);

HashMap<String, Object> map = new HashMap<String, Object>();
map.put("title","Java如此简单");
map.put("author","狂神说");
map.put("views",9999);
List<Blog> blogs = mapper.queryBlogChoose(map);

System.out.println(blogs);

session.close();
}

@Test
public void testQueryBlogForeach(){
SqlSession session = MybatisUtils.getSession();
BlogMapper mapper = session.getMapper(BlogMapper.class);

HashMap map = new HashMap();
List<Integer> ids = new ArrayList<Integer>();
ids.add(1);
ids.add(2);
ids.add(3);
map.put("ids",ids);

List<Blog> blogs = mapper.queryBlogForeach(map);

System.out.println(blogs);

session.close();
}