Question

你有一个职位表和一个职位表,两个职位都由一个职位——职位表挂钩。

......

员额

tags has id/name

职位——主 id/post_id/tag_id

in rails terminology, I have a Post Model that has many Tags through AssetTags.

I m trying to query for a post that has 2 specific tags. ......if there is a rails tag and a mysql tag, I want a query that returns a post that only has those two tags.

说明

这样做的任何方法(使用搜索逻辑的Im)或神秘性?

Answer 1

这一结构将包含两个方面的员额归来。

select 
  p.* 
from 
  posts p
  ,asset_tags atg1
  ,asset_tags atg2
  ,tags t1
  ,tags t2
where
  p.id = atg1.post_id
and t1.id = atg1.tag_id
and t1.tag =  MySQL  
and p.id = atg2.post_id
and t2.id = atg2.tag_id
and t2.tag =  Rails 
;

至于通过积极记录进行这项工作,一种替代办法是询问每一方,然后到处;由此形成的阵列,以找到双方的交汇点。

Answer 2

鉴于这些模式:

def Post
  has_many :asset_tags
  has_many :tags, :through => :asset_tags
end

def AssetTag
  has_one :post
  has_one :tag
end

def Tag
  has_many :asset_tags
  has_many :posts, :through => :asset_tags
end

你可以这样做:

Post.joins(:asset_tags => :tag).where(
  "tags.name in ( ? ,  ? )",  foo ,  bar  )

现在,这实际上与<条码>s_many :通过协会——我不敢肯定,如果有哪怕是一只微薄的皮,那么就没有。

Answer 3

For mysql, sure, you can get the data

 SELECT p.*
   FROM posts p 
   JOIN post_tags pt
     ON p.post_id = pt.post_id
  WHERE pt.tag_id in (tagId1, tagId2)

我没有使用铁路主动通融,但我相信,这将符合铁路线。

 get( posts );
 join( post_tags , post_id );
 where_in( tag_id , array(tagId1, tagId2);
 execute();

Answer 4

John Bachir的答复可修改为......

Post.joins(:asset_tags => :tag)
    .where("tags.name in ( ? )",  foo )
    .where("tags.name in ( ? )",  bar )

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