has_and_belongs_to_many，避免连接表中的重复 [英] has_and_belongs_to_many, avoiding dupes in the join table

问题描述

我有一组非常简单的 HABTM 模型

I have a pretty simple HABTM set of models

class Tag < ActiveRecord::Base 
   has_and_belongs_to_many :posts
end 

class Post < ActiveRecord::Base 
   has_and_belongs_to_many :tags

   def tags= (tag_list) 
      self.tags.clear 
      tag_list.strip.split(' ').each do 
        self.tags.build(:name => tag) 
      end
   end 
end 

现在一切正常，只是我在标签表中得到了大量重复项.

Now it all works alright except that I get a ton of duplicates in the Tags table.

我需要做什么来避免标签表中的重复(基于名称)?

What do I need to do to avoid duplicates (bases on name) in the tags table?

推荐答案

我通过创建一个 before_save 过滤器来解决这个问题.

I worked around this by creating a before_save filter that fixes stuff up.

class Post < ActiveRecord::Base 
   has_and_belongs_to_many :tags
   before_save :fix_tags

   def tag_list= (tag_list) 
      self.tags.clear 
      tag_list.strip.split(' ').each do 
        self.tags.build(:name => tag) 
      end
   end  

    def fix_tags
      if self.tags.loaded?
        new_tags = [] 
        self.tags.each do |tag|
          if existing = Tag.find_by_name(tag.name) 
            new_tags << existing
          else 
            new_tags << tag
          end   
        end

        self.tags = new_tags 
      end
    end

end

它可以稍微优化以批量处理标签，也可能需要一些更好的事务支持.

It could be slightly optimised to work in batches with the tags, also it may need some slightly better transactional support.

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