Ruby on Rails

Thanks for the input.  My question was only about the example in my book which indicated that the config of 't.references :<tablename>' would work for the 'dumb' join.  What I found was that AR was looking for the appended '_id' for the t.references config.  I received a reply here that confirmed the config in the book is valid, so it was probably an issue I caused myself somewhere.  I haven't had the chance to try it again but I plan to do so tomorrow.  Being new to the rails framework and ruby language I'm concerned with knowing when and how I can use certain constructs, which is why I'm picking on this particular example.  Although I might not use the dumb join often, it could happen.

BR

On Sunday, January 26, 2014 1:26:28 PM UTC-5, Walter Lee Davis wrote:

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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