[英]rails: Get all items tagged x AND y AND z
I've got two models: Item
and Tag
. 我有两个型号:
Item
和Tag
。 Both have a name attribute. 两者都有name属性。 I want to find items tagged with several tags.
我想找到标有多个标签的商品。
class Item < ActiveRecord::Base
has_many :tags
validates_presence_of :name
end
class Tag < ActiveRecord::Base
belongs_to :item
validates_presence_of :name
end
Given a list of tag ids, I can easily enough get the list of items tagged with one tag or the other: 给定一个标签ID列表,我可以很容易地获得用一个标签或另一个标签标记的项目列表:
# Find the items tagged with one or more of the tags on tag_ids
Item.all(:conditions => ['tags.id in (?)', tag_ids], :joins => :tags)
If tag_ids
is {1,4}
, then I get all pictures tagged with 1, or 4, or both. 如果
tag_ids
为{1,4}
,那么我tag_ids
所有图片标记为1或4或两者。
I want to know now how to get the pictures that are tagged with both - 1 AND 4. 我现在想知道如何获得用-1 和 4标记的图片。
I can't even imagine the SQL that is needed here. 我甚至无法想象这里需要的SQL。
You can solve this by grouping the results and checking the count: 您可以通过对结果进行分组并检查计数来解决此问题:
Item.all(
:conditions => ['tags.id IN (?)', tag_ids],
:joins => :tags,
:group => 'items.id',
:having => ['COUNT(*) >= ?', tag_ids.length]
)
Little update : Today, we can use (inspired by elektronaut) : 小更新:今天,我们可以使用(灵感来自elektronaut):
Item.joins(:tags).where("tags.label in (?)", tags).group('items.id').having("COUNT(*) >= ?", tags.size)
It is not very different, by it works well here. 它并没有太大的不同,它在这里运作良好。
I've got one thing to add to elektronaut's otherwise wonderful answer: it will not work on PostgreSQL. 我有一件事要添加到elektronaut的其他很好的答案:它不适用于PostgreSQL。
On my real example the Item.all call includes other tables; 在我的实例中,Item.all调用包括其他表; so the select looks like this:
所以select看起来像这样:
SELECT items.id AS t0_f0, items.name as t0_f1 ..., table2.field1 as t1_f0 .. etc
PostgreSQL's GROUP BY requires that all fields used on a select to be included there. PostgreSQL的GROUP BY要求将select上使用的所有字段都包含在那里。 So I had to include all the fields used on the previous select on the GROUP BY clause.
所以我必须在GROUP BY子句中包含上一个select中使用的所有字段。
And still it didn't work; 它仍然没有用; I'm not sure why.
我不知道为什么。
I ended up doing a simpler, uglier thing. 我最终做了一个更简单,更丑陋的事情。 It requires two db requests.
它需要两个db请求。 One of them is used to return ids, which are used as a condition.
其中一个用于返回id,它们用作条件。
class Item < ActiveRecord::Base
# returns the ids of the items tagged with all tags
# usage: Item.tagged_all(1,2,3)
named_scope :tagged_all, lambda { |*args|
{ :select => "items.id",
:joins => :tags,
:group => "items.id",
:having => ['COUNT(items.id) >= ?', args.length],
:conditions => ["tags.id IN (?)", args]
}
}
Then I can do this: 然后我可以这样做:
Item.all(
:conditions => [
'items.id IN (?) AND ... (other conditions) ...',
Items.tagged_all(*tag_ids).collect(&:id),
... (other values for conditions) ...
],
:includes => [:model2, :model3] #tags isn't needed here any more
)
Hacky, but it works, and the hackyness is localized. Hacky,但它有效,而hackyness是本地化的。
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