Rails - Active Record Join across 3 Tables

Question

somewhat new to Rails, so I'd appreciate any help you guys could offer.

Anyway, I have three models - Vote, Lunch, and Provider, and I'm looking to write a single Active Record call to pull:

• All the data in the Vote table
• The Lunch date in the Lunch table
• The Provider name in the Provider table

The Vote model includes a lunch_id, the Lunch model includes a lunch_id (just called id) and the provider_id. The Provider model has a provider_id (just called an id.) In the Rails console, I can write:

v = Vote.joins(:lunch).select("lunches.date,votes.*").where(lunch_id: 1)

and that outputs all the data in the Vote model, plus the associated date from the Lunch model. Where I'm stuck is that I don't know how to "nest" this to then join to the Provider model.

I'm thinking this may have something to do with "has_many_through", but even after reading the documentation, I'm not sure how it would be implemented. Any thoughts here would be greatly appreciated!

Answer 1

Assuming all of your models have the correct has_many and belongs_to associations defined, you can join in multiple tables by passing in a hash to the join method instead of just a symbol.

Vote.joins(lunch: :provider).select('lunches.date, providers.name, votes.*').where(lunch_id: 1)

More information about these can be found in the 'Using Array/Hash of Named Associations' portion of the rails query inferface documentation.

http://guides.rubyonrails.org/active_record_querying.html#using-array-hash-of-named-associations