Question

I’m working with a model structure that is not exactly ideal (i.e. I didn’t create it) and I’m having a hard time writing an AR query to get me the data I want…

I’ve got the following models:

class Project < ActiveRecord::Base
  has_many :project_states
  has_many :states, :through => :project_states
end

class State < ActiveRecord::Base
  has_many :forms
  has_many :project_states
  has_many :projects, :through => :project_states
end

class ProjectState < ActiveRecord::Base
  belongs_to :state
  belongs_to :project
end

class Form < ActiveRecord::Base
  belongs_to :state
end

Simple enough. Ish. What I’m trying to do is get a a list of all forms for all projects. Essentially let’s say I have two forms in the database, and 2 projects each of which has both forms. I’d like get the results:

-----------------------------------------------
project.name  |  state.name  |  form.name

Project 1        Ohio           Form 1
Project 1        California     Form 2
Project 2        Ohio           Form 1
Project 2        California     Form 2

I can do this quite easily with the following sql query:

SELECT 
  states.name, forms.name, projects.name 
FROM 
  forms 
LEFT JOIN 
  states ON forms.state_id = states.id 
INNER JOIN 
  project_states ON project_states.state_id = forms.state_id 
LEFT JOIN 
  projects ON projects.id = project_states.project_id;

But I’m not sure how to do this through AR. I could do it as a straight SQL query, but there are methods on the models I need for display. I could do it by simply fetching projects, looping over them and then looping over the forms for each one, but the display needs to be a sortable table and that would make it impossible to sort on any form attributes.

Is there an easyish way to implement this I’m missing? For example if I do something like:

Form.joins(:states=> [:projects])

This returns one result for each form, not one result for each form for each project. If I had a direct relationship between Projects and Forms, it would be easy enough as I could just fetch off the join table. But I don’t have that…

Answer 1

Follow up, I couldn’t really find a way to do this in rails without resorting to find_by_sql, so I ended up creating a view and a new model for the view to get the data I wanted.