I have these models:
Company; Categories; Classifications.
A Company has many categories and a Category has many companies. A Company for each of its own categories has a Classification. For example: Company-1 has Category-1 and Category-2. Company-1 - Category-1 has Classification-III while Company-1 - Category-2 has Classification IV. How can I declare associations?
Relevant documentation is here:
http://guides.rubyonrails.org/association_basics.html
(For similar results, google for “Rails Guides ”).
If I understand correctly, your case would be a perfect case for
has_many :through (and not habtm) because you need
Classification attributes on each association between a
Company and a Category (then the Classification table is
the association table between Company and Category).
Try to work out the code for your case from that documentation.
If you have difficulties with it, please come back with your specific
problems, showing us the code your wrote.
HTH,
Peter
I'm also was thinking about has_many :through. The join model is Classification with attriìbutes like: company_id category_id classification_type classification_amount.
But if classification.amount for classification.type II change I must change all the occurrences for company and categories where classification.type II occurs.
I think its better to use a join table like this: company_id category_id classification_id
What do you think about?
Indeed. I had not understood there are only a limited number of Classification types possible between the Company and the Category.
In that case, indeed it is better that the association table does
not have the Classification attributes itself, but you normalized out these attributes to a third Classification table (with the Classification#classification_type Classification.amount attributes).
WARNING: do not use ‘type’ as a column name, it is a special
column that is used for STI (Single Table Inheritance). Unless you would really want to use STI on your Classifications (which might make sense in an OO design if certain Classification types have special functionality that is different from other Classification
types).
HTH,
Peter