Rails complex SQL

I have couple of complex SQL and need to convert it into an ActiveRecord query. Please help me:

My models:

class Product < ActiveRecord::Base
  belongs_to :watch, :counter_cache => true
end

class Watch < ActiveRecord::Base
  belongs_to :category
  has_many :products
end

class Category < ActiveRecord::Base

  has_ancestry :cache_depth => true, :depth_cache_column => :depth

  has_many :watches, :dependent => :destroy
  has_many :products, :through => :watches

end

So Category have ancestry with two level deep, root is make and children is serie. My SQLs are following:

scope :by_make, lambda { |make_name| Product.find_by_sql("
    SELECT p.* FROM products p INNER JOIN watches w ON p.watch_id = w.id
      INNER JOIN categories series ON w.category_id = series.id
      INNER JOIN categories makes ON series.ancestry = makes.id
      WHERE makes.name LIKE '%#{make_name}%'
    ") unless make_name.blank? }

 scope :by_series, lambda { |series_name| Product.find_by_sql("
      SELECT p.* FROM products p INNER JOIN watches w ON p.w开发者_如何学编程atch_id = w.id
        INNER JOIN categories series ON w.category_id = series.id
        WHERE series.name LIKE '%#{series_name}%'
      ") unless series_name.blank? }

Please help to convert those into ActiveRecord queries, because it's very important not to get array on the end of query, thanks!

The most simple solution is just add where filter at the start of find_by_sql, something like that:

  scope :by_make, lambda { |make_name| where(:watch_id => Watch.find_by_sql("
    SELECT w.* FROM watches w
      INNER JOIN categories series ON w.category_id = series.id
      INNER JOIN categories makes ON series.ancestry = makes.id
      WHERE makes.name LIKE '%#{make_name}%'
    ")) unless make_name.blank? }

  scope :by_series, lambda { |series_name| where(:watch_id => Watch.find_by_sql("
      SELECT w.* FROM watches w
        INNER JOIN categories series ON w.category_id = series.id
        WHERE series.name LIKE '%#{series_name}%'
      ")) unless series_name.blank? } 

Should return AR collection.