[大数据]MyBatis——动态SQL

动态SQL

根据不同的条件生成不同的SQL语句

• if
• choose(when , otherwise)
• trim(where , set)
• foreach

环境搭建

• 导包

偷懒包

<dependency>
    <groupId>org.projectlombok</groupId>
    <artifactId>lombok</artifactId>
    <version>1.18.10</version>
</dependency>

• 编写配置文件(用之前的mabatis-config.xml 加这三条即可)

<setting name="mapUnderscoreToCamelCase" value="true"/>

<typeAlias type="net.cqwu.pojo.Blog" alias="blog"/>

<mapper class="net.cqwu.dao.BlogMapper"/>

• 编写实体类

import lombok.Data;

import java.util.Date;

@Data
public class Blog {
    private int id;
    private String title;
    private String autor;
    private Date dataTime;
    private int views;
    
    //getter.setter,构造器省略
}

• 编写实体类对应的Mapper接口和Mapper.xml文件

<insert id="addBlog" parameterType="blog">
    insert into mybatis.blog (id, title, author, create_time, views)
    values (#{id}, #{title}, #{author}, #{createTime}, #{views});
</insert>

• 先插几条数据进去

@Test
public void addBlog() {
    SqlSession sqlSession = MybatisUtils.getSqlSession();
    BlogMapper mapper = sqlSession.getMapper(BlogMapper.class);
    Blog blog = new Blog();
    blog.setId(IDutils.getId());
    blog.setTitle("Mybatis");
    blog.setAuthor("Feliks");
    blog.setCreateTime(new Date());
    blog.setViews(9999);

    mapper.addBlog(blog);

    blog.setId(IDutils.getId());
    blog.setTitle("Java");
    mapper.addBlog(blog);

    blog.setId(IDutils.getId());
    blog.setTitle("Spring");
    mapper.addBlog(blog);

    blog.setId(IDutils.getId());
    blog.setTitle("SpringMVC");
    mapper.addBlog(blog);

    sqlSession.commit();
    sqlSession.close();
}

IF

接口

//查询博客
List<Blog> queryBlogIF(Map map);

xml

<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

@Test
public void queryBlogIF(){
    SqlSession sqlSession = MybatisUtils.getSqlSession();
    BlogMapper mapper = sqlSession.getMapper(BlogMapper.class);

    HashMap map = new HashMap();
    map.put("title","MyBatis");
    map.put("author","Feliks");
    List<Blog> blogs = mapper.queryBlogIF(map);

    for (Blog blog : blogs) {
        System.out.println(blog);
    }

    sqlSession.close();
}

success

[net.cqwu.dao.BlogMapper.queryBlogIF]-==>  Preparing: select * from mybatis.blog where 1=1 and title = ? and author = ?
[net.cqwu.dao.BlogMapper.queryBlogIF]-==> Parameters: MyBatis(String), Feliks(String)
[net.cqwu.dao.BlogMapper.queryBlogIF]-<==      Total: 1
Blog(id=ccbf414acc3a44d9b26cd368dee7b108, title=Mybatis, author=Feliks, createTime=Sun Dec 05 21:35:37 CST 2021, views=9999)

choose(when , otherwise)

List<Blog> queryBlogChoose(Map map);

<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>

@Test
public void queryBlogChoose(){
    SqlSession sqlSession = MybatisUtils.getSqlSession();
    BlogMapper mapper = sqlSession.getMapper(BlogMapper.class);

    HashMap map = new HashMap();
    map.put("title","java针不戳");
    map.put("author","Feliks陈");
    map.put("views","9999");
    List<Blog> blogs = mapper.queryBlogChoose(map);

    for (Blog blog : blogs) {
        System.out.println(blog);
    }

    sqlSession.close();
}

[net.cqwu.dao.BlogMapper.queryBlogChoose]-==>  Preparing: select * from mybatis.blog WHERE title = ?
[net.cqwu.dao.BlogMapper.queryBlogChoose]-==> Parameters: java针不戳(String)
[net.cqwu.dao.BlogMapper.queryBlogChoose]-<==      Total: 1
Blog(id=2a2da62e7d784489b644ca8d35a9564e, title=Java针不戳, author=Feliks陈, createTime=Sun Dec 05 21:35:37 CST 2021, views=10000)

trim(where , 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>

    @Test
    public void updateBlog(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        BlogMapper mapper = sqlSession.getMapper(BlogMapper.class);

        HashMap map = new HashMap();
//        map.put("title","java针不戳啊");
        map.put("author","slugger");
        map.put("id","ccbf414acc3a44d9b26cd368dee7b108");

        mapper.updateBlog(map);
        sqlSession.commit();

        sqlSession.close();
    }

SQL片段

将一些功能的部分抽取出来，方便使用

1. 使用sql标签抽取公共部分

<sql id="if-title-author">
    <if test="title != null">
        title = #{title}
    </if>
    <if test="author != null">
        and author = #{author}
    </if>
</sql>

2. 在需要使用的对方使用include标签引用

<select id="queryBlogIF" parameterType="map" resultType="blog">
    select * from mybatis.blog
    <where>
        <include refid="if-title-author"></include>
    </where>
</select>

注意：

• 最好基于单表来定义SQL片段
• 不要存在where标签

Foreach

//查询第1，2，3号的记录的博客
List<Blog> queryBlogForeach(Map map);

<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);
    ids.add(2);
    ids.add(3);

    map.put("ids",ids);
    List<Blog> blogs = mapper.queryBlogForeach(map);

    for (Blog blog : blogs) {
        System.out.println(blog);
    }
    sqlSession.close();
}

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，去排列组合即可