DZone Snippets: habtm code

Using a mutiple collection select form helper with habtm or has many associations in Rails

davenolan (davenolan) — Mon, 30 Jul 2007 08:58:54 GMT

// where user has and belongs to many roles



# in your view

<%= collection_select :user, :role_ids, Role.find(:all, :order => 'name ASC'), :id, :name, { :selected => @user.role_ids }, { :multiple => true, :name => 'user[role_ids][]' } -%>

HABTM relationship MySQL tables for use in Rails

alexwilliams (Alex Williams) — Tue, 19 Dec 2006 15:14:13 GMT

This is an example of the tables I create when I want to have an HABTM relationship between 2 tables:
Table 1: products
Table 2: tags



DROP TABLE IF EXISTS `products_tags`;

DROP TABLE IF EXISTS `tags`;

DROP TABLE IF EXISTS `products`;



CREATE TABLE `products` (

  `id` int(11) NOT NULL auto_increment,

  `title` varchar(100) NOT NULL,

  `price` decimal(10,2) NOT NULL,

  PRIMARY KEY  (`id`)

)



CREATE TABLE `tags` (

  `id` int(11) NOT NULL auto_increment,

  `title` varchar(64) NOT NULL,

  PRIMARY KEY  (`id`)

)



CREATE TABLE `products_tags` (

  `product_id` int(11) NOT NULL default '0',

  `tag_id` int(11) NOT NULL default '0',

  PRIMARY KEY  (`product_id`,`tag_id`)

)

Toggling associations for Many-to-Many relationships

AndyV (Andy Vanasse) — Fri, 13 Oct 2006 21:24:26 GMT

I have a rather greedy object that needs to be associated with most of the other objects in my domain. To compensate, I've written the following code to take care of toggling the association (adding a record in the join table if it does not exist or removing it if it does). I've called it toggle because it's physically represented by toggling the state of a checkbox on a form.



def toggle_child_assoc(child_object)

    # check to see if the parent recognizes the collection_name

    collection_name = child_object.class.to_s.downcase.pluralize

    aCollection = self.send(collection_name) if self.respond_to?(collection_name)

    unless aCollection

      return false

    end



    # If the parent recognizes the collection_name then check to see if the child_object

    # appears in the collection.  If so then remove it, otherwise add it.

    if aCollection.include?(child_object)

      self.send("remove_%s" % collection_name, child_object)

    else

      self.send("add_%s" % collection_name, child_object)

    end

    true

end

First the code determines if the "parent" of the association actually supports a collection of the child object's class by testing to see if it responds to the method corresponding to the name of the collection. If not the method returns false. Otherwise, the method checks to see if the parent object already has the child in its collection. If it does it builds a call to remove_collection_name to remove it and if it does not it builds a call to add_collection_name to add it.

The code could be improved by adding a means by which to override the collection_name. This override would be used in the event that the child is a subclass of a class with which the parent has a habtm relationship.

Doing a has_and_belongs_to_many against a single table

peter (Peter Cooperx) — Sat, 14 May 2005 09:44:21 GMT

Found via the RoR wiki. Solution courtesy of Jakob S.

Assuming a schema like such:

create table node (

  id integer primary key,

  name varchar(32)

);



create table nodelink (

  source_id integer,

  destination_id integer

);

A Rails association like this would supposedly do the job:

has_and_belongs_to_many :nodes, :join_table => 'nodelink', :association_foreign_key => 'destination_id', :foreign_key => 'source_id'