Question

I have this relation in my Product model:

has_many :features, :class_name => 'ProductFeature', :source => :product_feature, :include => :feature

So I can do Product.features

which works fine. But I want to be able to filter that by fields in the feature table, when and if necessary. For example in pseudo code:

find all product features where feature is comparable

compare is a bool field on the feature.

I have been trying for 2 hours solid and cannot figure it out (without writing a new query completely). I can’t figure out how to access the feature table’s fields from the Product.features relation, as it seems it can only filter on product_features fields.

This is what I have come up with so far:

def features_compare
  features.feature.where(:compare => true)
end

But it just says feature is not a valid method, which I understand.

Edit

I have updated my model so the relationships are clearer:

product.rb:

class Product < ActiveRecord::Base
  belongs_to :company
  belongs_to :insurance_type

  has_many :product_features
  has_many :reviews

  attr_accessible :description, :name, :company
end

product_feature.rb:

class ProductFeature < ActiveRecord::Base
  belongs_to :product
  belongs_to :feature

  delegate :name, :to => :feature

  attr_accessible :value
end

feature.rb

class Feature < ActiveRecord::Base
  attr_accessible :name, :compare
end

I want to be able to query the product_features that belong to a product and feature where Feature.compare is true. Something like this:

product.rb

def features_compare
  product_features.where(:compare => true)
end

This throws an error because compare in in the Feature model, not ProductFeature. I have tried the following in product_feature.rb:

delegate :compare, :to => :feature

but I didn’t help.

I will adding a bounty to this in a few hours so please please help me!

Answer 1

find all product features where feature is comparable is just

ProductFeature.joins(:feature).where(:feature => {:compare => true})

You can make that a bit more reusable by introducing a scope:

#in product_feature.rb
scope :with_feature_like, lambda do |filter|
   joins(:feature).where(:feature => filter)
end

#elsewhere
ProductFeature.with_feature_like(:compare => true)

#all the product features of a certain product with at comparable features
some_product.product_features.with_feature_like(:compare => true)

Finally, if you want all products with product features with comparable features, you want something like:

Product.joins(:product_features => :feature).where(:feature => {:compare => true})

which of course you can also turn into a scope on Product.