Implementing a tagging system in Rails

This is a copy/paste from my question over at StackOverflow so feel free to answer there if you want some reputation.

I’m trying to implement a tagging system in a Rails app similar to the one StackOverflow uses (where users enter in tags in a freeform textbox). I’m aware that there are gems that can do this, but I wanted to try to implement it myself for the learning experience. I got it to work, but since I’m a Rails newbie I’m concerned I’m not doing it the “right way”.

Here’s my current implementation:

def Post
  attr_accessor :tag_names

  has_and_belongs_to_many :tags

  after_save :update_tags

  private
    def update_tags
      tags.delete_all

      if tag_names.to_s == ''
        return
      end

      tag_names.split(/,/).each do |tag_name|
        tag_name.strip!
        tag = Tag.find_or_create_by_name(tag_name)

        if !tags.exists?(tag.id)
          tags << tag
        end
      end
    end
end

This makes it easy for me to set up the tags for a post since all I have to do is set the “tag_names” attribute on my post object. When I save the post object, the after_save event fires and executes my update_tags function which then handles creating tags and linking the post to them.

Are there any problems with my implementation?


This is a copy/paste from my question over at StackOverflow so feel free to answer there if you want some reputation.
I’m trying to implement a tagging system in a Rails app similar to the one StackOverflow uses (where users enter in tags in a freeform textbox). I’m aware that there are gems that can do this, but I wanted to try to implement it myself for the learning experience. I got it to work, but since I’m a Rails newbie I’m concerned I’m not doing it the “right way”.

Here’s my current implementation:

def Post
  attr_accessor :tag_names

  has_and_belongs_to_many :tags


  after_save :update_tags

  private
    def update_tags
      tags.delete_all

      if tag_names.to_s == ''

        return
      end

      tag_names.split(/,/).each do |tag_name|

        tag_name.strip!
        tag = Tag.find_or_create_by_name(tag_name)


        if !tags.exists?(tag.id)
          tags << tag

        end
      end
    end
end

This makes it easy for me to set up the tags for a post since all I have to do is set the “tag_names” attribute on my post object. When I save the post object, the after_save event fires and executes my update_tags function which then handles creating tags and linking the post to them.

Are there any problems with my implementation?



You’re deleting the tag records on every save. So other posts which belong to the tags you deleted would

most probably throw an error when you try to access the tags (or will they silently update the the post’s tags?).

Anyway, you need to have access to the join table and delete the records created there instead of deleting

the tag records when updating the post record.

I don’t know if it would improve performance, but instead of deleting all tags of the post, why not compare the

post’s current tags first and create/associate a tag to the post if it’s not yet associated?

I don’t think this is true. According to the Rails API, this is what collection.delete does with a has_and_belongs_to_many association:

“Removes one or more objects from the collection by removing their
associations from the join table. This does not destroy the objects.”

I went ahead and tested this out just to make sure and sure enough, only the association was deleted when I called save, not the tag itself.

Just to be sure though, I’ve changed that line to be:

tags.clear

This seems cleaner anyways, and the Rails API explicitly states that calling this will not delete the objects themselves, only the association.

Just to be sure though, I’ve changed that line to be:

tags.clear

this sure make things clearer. i should’ve checked the api before i commented.