Doing something before saving a form used with HABTM - ruby-on-rails

Question

I currently have 3 tables.
snippet
tags
snippet_tags
I'm using HABTM.
So I did a form to save a snippet with tags. Keywords are in a text field, separated by commas.
What I need to do is to take the string from this text field, loop on the keywords, check if they exist, if not create them, and THEN save the snippet.
I tried with a before_save but it doesn't seem to go by that way..
So if you could help me, it'd great!
Thanks a lot!

Answer 1

I think JosephL's answer is pretty good. Although, I would do it all in the snippets_controller action:
def create
#snippet = Snippet.new(params[:snippet])
#snippet.tags = params[:tags].split(',').collect { |tag| Tag.find_or_create_by_name(tag) }
if #snippet.save
# do something when successful
else
# do something when saving failed
end
end
Sorry for that long, one-line statement. ;-)
I didn't test the code, but I hope it works.
Tag.find_or_create_by_name will do exactly that: when a tag with that name exists, it will return it, otherwise it will create the new tag on the fly and return that.
This way, the tags are already saved, before you call #snippet.save.
Please note, that I just assumed, how your variables and parameters are named.

Answer 2

Here is a version of your create method. The main change is not creating a Snippet_Tag. If your HABTM association is set up correctly then your snippet will have a tags collection which you can add your tags to. The collection will be persisted as Snippet_Tags by ActiveRecord. See the rails associations guide for more details on HABTM associations.
def create
# Creating the snippet
#snippet = Snippet.new
#snippet.title = params[:snippet][:title]
#snippet.content = params[:snippet][:content]
# loop through the tags
params[:snippet][:tags].split(',').collect do |tag_string|
tag_string.strip!
if tag_string.length > 0
# Find or create tag
tag = Tag.find_or_create_by_name(tag_string)
# Add tag to tags collection
#snippet.tags << tag
end
end
if #snippet.save
# do something when successful
else
# do something when saving failed
end
end

Answer 3

Use split to break your string into an array of the tags
Find each tag by name
If not found then create the tag
Add the tag to the snippet
Save the snippet (in your controller)
Example method to put in your snippet model
def add_tags(tag_list_string)
tag_array = tag_list_string.split ','
tag_array.each do |tag_name|
tag = (Tag.find_by_name(tag_name) || Tag.create(:name => tag_name))
self.tags << tag
end
end

Answer 4

Try before_update?