选择带有多个标签的帖子 [英] Selecting posts with multiple tags

问题描述

我正在博客应用中实施标记系统。这个程序有帖子，帖子有很多通过标签标记。或多或少像RailCasts＃382 http://railscasts.com/episodes/382-tagging

I'm implementing a tagging system on a blog app. This app has posts, posts have many tags through taggings. More or less like RailCasts #382 http://railscasts.com/episodes/382-tagging

我将使用复选框选择带有多个标签的帖子，如下所示：

I will use checkboxes to select posts with multiple tags like this:

Post.joins(:tags).where(:tags => { :id => [tag_ids] } )

但是，如果我想加入具有所有必需标签的帖子，而不是仅满足一个要求的帖子，该怎么办？

But what if I want to join posts that have all the required tags instead of posts that meet only one requirements?

例如：

Post1具有标签 foo，bar，baz

Post1 has tags "foo, bar, baz"

Post2具有标签 bar，baz

Post2 has tags "bar, baz"

Post3具有标签 bar

Post3 has tags "bar"

如果我搜索[ bar， baz]，我的方法将返回帖子1， 2和3。如果我只想返回帖子1和2？

If I search for ["bar", "baz"] my method returns posts 1, 2 and 3. What If I want to return only post 1 and 2?

推荐答案

在SQL中，您会执行以下操作： / p>

In SQL, you would do something like

GROUP BY posts.id
HAVING count(tags.name) = 2

在栏杆中表示为

Post.joins(:tags).select('posts.id').where(:tags => { :id => [tag_ids] }
).having("count(tags.name) = ?", tag_ids.count).group('posts.id')

上面的代码假定 tag_ids 是一个ID数组。此外，它仅加载返回的ActiveRecord Post对象集的ID。

The above code assumes that tag_ids is an array of ids. Also, it only loads the ids for the returned set of ActiveRecord Post objects.

如果要加载更多字段，请在 select中添加它们调用，否则删除 select 调用以加载所有帖子字段。只需记住，对于在结果SQL查询中检索到的Post中的每个列/字段，您都需要将该字段添加到 group 调用中。

If you want to load more fields, add them in the select call, or otherwise remove the select call to load all Post fields. Just remember that for every column/field from Post that is retrieved in the resulting SQL query, you will need to add that field to the group call.

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