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(); }