Rails 4-通过关联预加载has_many失败，并且穿透表的lambda条件

Question

I have the following structure and am trying to include a has_many :through association. It works properly if I don't preload the collections , but then I'm faced with an N+1 problem.

How can I pass conditions of the parent products association into the lambda when selecting collections ?

class Collection < ActiveRecord::Base
  # == Schema Information
  #
  # Table name: products
  #  name                :string(255)      not null

  has_many    :products,
                inverse_of:     :collection

  has_many    :product_lines,
                through:        :products,
                inverse_of:     :products

  has_many    :lines,
                through:        :product_lines,
                inverse_of:     :product_lines
end


class Product < ActiveRecord::Base
  # == Schema Information
  #
  # Table name: products
  #  active              :boolean          default(TRUE), not null

  belongs_to  :collection,
                inverse_of:     :products

  has_many    :product_lines,
                inverse_of:     :product

  has_many    :lines,
                through:        :product_lines,
                inverse_of:     :product_lines
end


class ProductLine < ActiveRecord::Base
  belongs_to  :product,
                inverse_of:     :product_lines

  belongs_to  :line,
                inverse_of:     :product_lines
end


class Line < ActiveRecord::Base
  has_many    :product_lines,
                inverse_of:     :line

  has_many    :products,
                through:        :product_lines,
                inverse_of:     :product_lines

  # Gets Collections through Products where `product.active = true`
  # And orders the Collections by `collection.name`
  has_many    :collections,
                -> { where( products: {active: true} ).order(name: :ASC) },
                through:        :products,
                inverse_of:     :products

end

Works:

Line.all.each{ |line| line.collections }

Doesn't work:

Line.includes(:collections).all.each{ |line| line.collections }

Throws error:

ActiveRecord::StatementInvalid - PG::UndefinedTable: ERROR:  missing FROM-clause entry for table "products"
LINE 1: SELECT "collections".* FROM "collections" WHERE "products"."...
                                                        ^
: SELECT "collections".* FROM "collections" WHERE "products"."active" = $1 AND "collections"."id" IN (11, 30, 27, 12, 10, 13, 6, 4, 2, 7, 15, 9, 19, 1, 14, 8, 31, 5, 3, 29, 20, 17, 16, 37, 38, 41, 42, 43, 18, 44, 45, 26, 24, 25, 21, 22, 23):

Answer 1

Turns out I'm just an idiot. All I had to do is include(:products) in the lambda. The working solution is below, and was further DRYed up by moving the logic for selecting collections through products into the named scope :by_active_products on Collections . Both methods work with preloading and neither causes an N+1 issue.

class Collection < ActiveRecord::Base
  # == Schema Information
  #
  # Table name: products
  #  name                :string(255)      not null

  has_many    :products,
                inverse_of:     :collection

  has_many    :product_lines,
                through:        :products,
                inverse_of:     :products

  has_many    :lines,
                through:        :product_lines,
                inverse_of:     :product_lines

  scope       :by_active_products, -> () { 
                includes(:products)
                .where({products: {active: true}})
                .order(name: :ASC)
                .uniq
              }
end


class Product < ActiveRecord::Base
  # == Schema Information
  #
  # Table name: products
  #  active              :boolean          default(TRUE), not null

  belongs_to  :collection,
                inverse_of:     :products

  has_many    :product_lines,
                inverse_of:     :product

  has_many    :lines,
                through:        :product_lines,
                inverse_of:     :product_lines
end


class ProductLine < ActiveRecord::Base
  belongs_to  :product,
                inverse_of:     :product_lines

  belongs_to  :line,
                inverse_of:     :product_lines
end


class Line < ActiveRecord::Base
  has_many    :product_lines,
                inverse_of:     :line

  has_many    :products,
                through:        :product_lines,
                inverse_of:     :product_lines

  # Gets Collections through Products where `product.active = true`
  # And orders the Collections by `collection.name`
  has_many    :collections,
                # Working using a named scope in the Collection model
                ->              { Collection.by_active_products },
                # Also working; Query params directly in the lambda
                # -> { includes(:products).where(products: {active: true}).order(name: :ASC).uniq },
                through:        :products,
                inverse_of:     :products

end

Working now:

Line.includes(:collections).all.each{ |line| line.collections }