Help with ActiveRecord for Models with long associtation chain

rubyonrails-talk
1

Hi,

I am trying to use this set of associations for what must be a fairly standard data model, to give me the accessor @batch.products

Batch:   has_many :orders   has_many :line_items :through=>orders Order:   has_many :line_items   belongs_to :batch   has_many :products, :through=>:line_items LineItem:   belongs_to :product   belongs_to :order Product::   has_many :line_items

OK I think they are the main associations involved.

I sort of want to say that Batch has_many :products, :through=>orders, :through=>line_items

This doesnt work and I have tried other variations. The only way i can think at the moment is to make products into a named scope using an sql find, but I am sure there must be a way of telling AR how to do the joins without using sql.

TRANSACTION question? I want to get to @batch.products so that I can iterate through each product and update the product stock quantities based on the line_item quantities. Then mark the batch as updated and finally commit as a single batch save. My thinking being that this would be carried out as a safe transaction. The alternative, would be to build a specific transaction, but I am not sure how to do this across 2 models (ie Batch and Product)

All help much appreciated. Tonypm

2

Hi,

OK I think they are the main associations involved.

I sort of want to say that Batch has_many :products, :through=>orders, :through=>line_items

This doesnt work and I have tried other variations. The only way i can think at the moment is to make products into a named scope using an sql find, but I am sure there must be a way of telling AR how to do the joins without using sql.

has_many :through can't be nested (I've vague feeling there's a plugin that does this). You could probably simplify the find down by using :joins (ie something like Product.find :all, :joins => {:line_items => {:order => :batch}},                          :conditions => {'batch.id' => some_batch_id

TRANSACTION question? I want to get to @batch.products so that I can iterate through each product and update the product stock quantities based on the line_item quantities. Then mark the batch as updated and finally commit as a single batch save. My thinking being that this would be carried out as a safe transaction. The alternative, would be to build a specific transaction, but I am not sure how to do this across 2 models (ie Batch and Product)

Unless batch and product are in different databases, Batch.transaction and Product.transaction are exactly the same. If you don't like 'preferring' one over the other you could always do ActiveRecord::Base.transaction do   ... end

Fred

3

Fred,

thanks for very quick response. That clarifies things and helps me move forward.

Actually my update is complicated further, since a line_item can be a packet with a bill of materials of several products so transaction will be the way to go. and I see I dont need to worry about tables since the transaction is on the actual connection not the database.

Many Thanks Tonypm

4

Fred - Oh and by the way!

Product.find :all, :joins=>{:line_items=>{:order => :batch}}, :conditions=>{'batches.id'=>361}

worked perfectly - wouldnt have figured that out myself!

Thanks Tonypm