Ruby on Rails

On Jan 25, 2014, at 11:45 PM, Martin Sloan wrote:

> Blaine,
>
> Thanks for the post. The book I'm reading followed up the basic join example (many-to-many) with a 'rich' join (has_many :through). From what I understand there's a scenario for both and they're similar but there are differences. In the book's example the articles and categories tables are 'meeting up' at the articles_categories table and not 'going through' to reference another table.

HABTM joins are used for "dumb" joins, where you want a two-way relationship between two tables that does not carry any further information about its connection. Most real-world connections aren't that dumb, and so the general advice is to use a HMT connection to "educate" that join. Person -> has many Clubs -> through Membership would be a simple example. Membership can have a member type picker, a date joined, date kicked out of the club for unsportsman-like conduct, whatever other "smart" attributes the real relationship might need to carry.

Walter

>
> Thanks
>
> On Friday, January 24, 2014 4:39:28 PM UTC-5, Blaine LaFreniere wrote:
>
> On 1/24/14, 11:25 AM, Martin Sloan wrote:
>> Hello,
>>
>> I'm new to Ruby/Rails and going through 'Beginning Rails 4'. In chapter 6 it has me create a join table for an articles and categories table (articles_categories). In the migrate file I've entered this code from the book:
>>
>> class CreateArticlesCategories < ActiveRecord::Migration
>> def change
>> create_table :articles_categories, :id=> false do |t|
>> t.references :article
>> t.references :category
>> end
>> end
>> def self.down
>> drop_table :articles_categories
>> end
>> end
>>
>> My issue is that after I migrate this file, when I try to make an association between the article and category object (article.categories << category) it spits an error that article_id does not exist in articles_categories table. It makes sense to me since the references above do no have _id appended in the class. If I change the class to the following, creating the relationship between article and category works fine:
>>
>> class CreateArticlesCategories < ActiveRecord::Migration
>> def change
>> create_table :articles_categories, :id=> false do |t|
>> t.integer :article_id
>> t.integer :category_id
>> end
>> end
>> def self.down
>> drop_table :articles_categories
>> end
>> end
>>
>> My question is, how can I get the 't.references' format to work so that AR looks for an 'articles' and 'categories' column, instead of the same with _id appended?
>
> You need to use has_many :through when working with join tables, not has_and_belongs_to_many. The :through parameter specifies the join table.
>
> See this section of the Rails guide: http://guides.rubyonrails.org/association_basics.html#the-has-many-through-association
>
> --
> • Blaine LaFreniere
> • Phone: 801-448-6124
> • E-mail: brlafr...@gmail.com
> • Web: brlafreniere.com
>
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