如何基于模型的相关数据提取条目？ （路轨）

Question

Let's suppose I have a Discussion model, and that a discussion can be tagged. These tags are associated to the discussion through a taggings table.

I want to define a method .tagged_with(tag) that will basically do:

 def tagged_with

      Discussion.where(#something about tags include the tag given)
 end

I do have some methods that might be helpful already set up. For example, I have tag_list

 def tag_list
     tags.map(&:name).joins(", ") #my tags are separated by commas, not spaces)
 end

And if someone knows an answer to the simpler question of trimming the Discussion model based off one tag, how can I expand it to be more adaptable - for example, accepting an argument of multiple tags, and being able to specify that any or all are necessary. EG:

 Discussion.tagged_with(tag1, tag2, :any => true)

FYI some of the code from the associations:

has_many :taggings, :as => :taggable
has_many :tags, :through => :taggings, :source => :tag, :source_type => "Tag"

Answer 1

You should be able to join the tags table into your Discussion query, through its has_many relationship. Discussion.joins(:tags).where(:tags => {:name => array_of_tags}) .

With the below method definition, you can do something like Discussion.tagged_with(['foo', 'bar']) or Discussion.tagged_with('foo') .

def self.tagged_with(tag_or_tags)
  joins(:tags).where(:tags => {:name => tag_or_tags})
end