```ruby
module Spree
  module Scopes
    module Variant

      #FIXME WARNING tested only under sqlite and postgresql
      Spree::Variant.scope :descend_by_popularity, lambda {
        order('COALESCE((SELECT COUNT(*) FROM  line_items GROUP BY line_items.variant_id HAVING line_items.variant_id = variants.id), 0) DESC')
      }

      # for selecting variants with an option value
      # no option type given since the value implies an option type
      # this scope can be chained repeatedly, since the join name is unique
      Spree::Variant.scope :has_option, lambda {|opt|
        tbl = 'o' + Time.now.to_i.to_s + Time.now.usec.to_s
        { :joins => "inner join option_values_variants as #{tbl} on variants.id = #{tbl}.variant_id",
          :conditions => ["#{tbl}.option_value_id = (?)", opt]
        }
      }
    end
  end
end
```

Fix calls to Variant model in Spree::Scopes::Variant
user
```ruby
module Spree
  module Scopes
    module Variant

      #FIXME WARNING tested only under sqlite and postgresql
      Spree::Variant.scope :descend_by_popularity, lambda{
        order('COALESCE((SELECT COUNT(*) FROM  line_items GROUP BY line_items.variant_id HAVING line_items.variant_id = variants.id), 0) DESC')
      }

      # for selecting variants with an option value
      # no option type given since the value implies an option type
      # this scope can be chained repeatedly, since the join name is unique
      Spree::Variant.scope :has_option, lambda {|opt|
        tbl = 'o' + Time.now.to_i.to_s + Time.now.usec.to_s
        { :joins => "inner join option_values_variants as #{tbl} on variants.id = #{tbl}.variant_id",
          :conditions => ["#{tbl}.option_value_id = (?)", opt]
        }
      }
    end
  end
end
```
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