group by sum of products of child model attributes

Question

Document has_many :items

Item belongs_to :document

I need to find documents, in which the sum of products of its items.quantity * items.value_net is greater than certain value.

I tried scope:

scope :items_value_net_gteq, lambda { |value|
  joins(:items)
    .where('SUM(items.quantity * items.price_net) >= ?', value)
}

But it is wrong. I must be missing something obvious.

Answer 1

You are looking for having (not tested):

scope :items_value_net_gteq, ->(value) {
  joins(:items).group('documents.id').
    having('SUM(items.quantity * items.price_net) >= ?', value)
}

Answer 2

scope :items_value_net_gteq, lambda do |value|
  joins(:items).group("items.document_id")
         .having('SUM(items.quantity * items.price_net) >= ?', value)
end