动态SQL:动态SQL就是指根据不同的条件生成不同的SQL语句
if
choose (when, otherwise)
trim (where, set)
foreach
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
@Data
public class Blog {
private String id;
private String title;
private String author;
private Date createTime;// 属性名和字段名不一致
private int views;
}
<select id="queryBlogIF" parameterType="map" resultType="blog">
select * from mybatis.blog where 1 = 1
<if test="title != null">
and title = #{title}
if>
<if test="author != null">
and author = #{author}
if>
select>
@Test
public void queryBlogIF(){
SqlSession sqlSession = MybatisUtils.getSqlSession();
BlogMapper mapper = sqlSession.getMapper(BlogMapper.class);
HashMap map = new HashMap();
map.put("title","Java");
List<Blog> blogs = mapper.queryBlogIF(map);
for (Blog blog : blogs) {
System.out.println(blog);
}
sqlSession.close();
}
<select id="queryBlogChoose" parameterType="map" resultType="blog">
select * from mybatis.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="queryBlogIF" parameterType="map" resultType="blog">
select * from mybatis.blog
<where>
<if test="title != null">
and title = #{title}
if>
<if test="author != null">
and author = #{author}
if>
where>
select>
<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>
有时候,可能需要将一些公共的部分抽取出来,方便复用。
<sql id="if-title-author">
<if test="title != null">
and title = #{title}
if>
<if test="author != null">
and author = #{author}
if>
sql>
<select id="queryBlogIF" parameterType="map" resultType="blog">
select * from mybatis.blog
<where>
<include refid="if-title-author">include>
where>
select>
注意事项:
<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>
@Test
public void queryBlogForeach(){
SqlSession sqlSession = MybatisUtils.getSqlSession();
BlogMapper mapper = sqlSession.getMapper(BlogMapper.class);
HashMap map = new HashMap();
ArrayList<Integer> ids = new ArrayList<Integer>();
ids.add(1);
map.put("ids",ids);
List<Blog> blogs = mapper.queryBlogForeach(map);
for (Blog blog : blogs) {
System.out.println(blog);
}
sqlSession.close();
}
动态SQL实际上就是在拼接SQL语句,只要保证SQL的准确性,按照SQL的格式,排列组合即可
思路:先写出完整的SQL,再去改写为动态SQL