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Question

I think this is a lot simpler than the title probably lets on. Here are my three models with the associations:

Update : associations were incorrect previously. Here are the corrected associations:

#app/models/call_service.category.rb
class CallServiceCategory < ActiveRecord::Base
  has_many :call_services
end

#app/models/call_service.rb
class CallService < ActiveRecord::Base
  belongs_to :call_service_category
  has_many :calls
end

#app/models/call.rb
class Call < ActiveRecord::Base
  belongs_to :call_service
end

So I have a group of call_ids for the calls I want:

@call_ids = [1,2,3,4]

Initial step which works :
What I want to do is grab only the calls with the ids specified in @call_ids . Then, I want to eager load only the associated call_services for those grabbed calls . The following does this perfectly:

@call_ids = [1,2,3,4]
@calls_by_service = CallService.includes(:calls).where("calls.id IN (?)", @call_ids).references(:calls)

This is great. Now I can iterate through only those selected calls' call_services , and I can even list all of those selected calls per service like so:

<% @calls_by_service.each do |call_service| %>
  <p> <%= call_service.description %> </p>
  <% call_service.calls.each do |call| %>
    <%= call.name %><br>
  <% end %>
<% end %>

What is great about this too is that @calls_by_service does not contain ALL of the call_services , but instead only those call_service records associated with the calls specified in @call_ids . Exactly what I want at this level.

One Level Deeper which is where I am having trouble:
This is great but I need to go one level deeper: I want to display only the associated call_service_categories for the associated call_services of those selected calls specified by @call_ids .

In other words: I want to grab only the calls with the ids specified in @call_ids . Then: I want to eager load only the associated call_services for those grabbed calls . Then: I want to eager load only the associated call_service_categories for those grabbed calls .

A visual of the structure is like this:

So I want to be able to iterate through those associated call_service_categories (ex: 'Emergency Relief', 'Employment'), and then iterate through the associated call_services of those calls specified in the @call_ids , and then display those calls per service.

I figured out one level (by call_service), now I just need to figure out one level deeper (by call_service_category).

In the rails guides, I attempted looking at the section on specifying conditions on eager loaded associations . I was not having success, but I think the answer is in that section.

Any help is much appreciated. Thanks!

Answer 1

One of the belongs_to associations (in CallService or Call ) should be actually a has_one (one-to-one relationship – belongs_to on the one side and has_one on the other). Apart from that, you can try the following code to produce a chained query with left join s and retrieve fields from all 3 tables:

CallServiceCategory.includes(call_services: :calls)
                   .where(calls: {id: @call_ids})
                   .references(:call_services, :calls)

I've noticed that you have a through association on your CallServiceCategory model, but as there would be no :call_services in includes , you can't reference fields from CallService model in references (you can, but they just won't appear in the actual sql query).