Problems with destroy and relationships

rubyonrails-talk
#1

Hi all,

    I am running into problems with my model relationships and
destroying them. In particular:

class Campaign < ActiveRecord::Base
  has_and_belongs_to_many :tags
  has_and_belongs_to_many :geographies
end

class Tag < ActiveRecord::Base
  has_and_belongs_to_many :campaigns
end

class Geographies < ActiveRecord::Base
  has_and_belongs_to_many :campaigns
end

class TagController < ApplicationController
...
def destroy

tag = Tag.find(:first, :conditions => ["id = ?",params[:id]])
    tag.connection.delete("DELETE FROM campaigns_tags WHERE tag_id =
'"+tag.id.to_s+"'") if tag.connection.execute("SELECT * FROM
campaigns_tags WHERE tag_id = '"+tag.id.to_s+"'")
    tag.connection.delete("DELETE FROM spotprofile_taggings WHERE
tag_id = '"+tag.id.to_s+"'") if tag.connection.execute("SELECT * FROM
spotprofile_taggings WHERE tag_id = '"+tag.id.to_s+"'")
    tag.destroy
    redirect_to session[:back_page]
end

So, I have a symmetric habtm relationship between campaigns and tags,
and campaigns and geographies. Why, when I attempt to "really"
destroy the tag in the next to last line of the controller, do I get
this stack trace?

A SystemStackError occurred in tag#destroy:

  stack level too deep
  /usr/lib64/ruby/gems/1.8/gems/activerecord-1.14.4/lib/active_record/
associations/association_proxy.rb:123:in `load_target'
.
.
.

#2

try has_many :through as an alternative…

http://blog.hasmanythrough.com/2006/04/20/many-to-many-dance-off

#3

I’m curious about something. I swear everywhere I look habtm is being taken out to the shed. Why is that? habtm is a perfectly valid relation and yet it seems like everyone is always suggesting has_many :through like it’s a fix all. has_many :through is a very clever habtm that appears only in situations where you have a class that has two belongs_to relationships to other classes that also wish to have a has_many relationship between them. I find myself with situations using habtm almost exclusively. I’m wondering if I’m just not doing a good job of modeling by not seeing this extra join model that should be appearing everywhere I have a habtm or is everyone else just looking for a way to use the new shiny object?

So to help answer the original question, first off I’d ask why you’re manually executing all that deletion SQL? If you want to delete a tag or campaign or whatever, just destroy it. Rails will delete the entry in the habtm join table for you automatically. If you need to delete a few of them and have it be atomic put the destroy calls in a transaction. Use the methods that AR gives you instead of managing it all yourself. You’re fighting with it instead of letting it help you :slight_smile:

Hope that helps,

-Michael

http://javathehutt.blogspot.com