Unresolvable trigger of N+1 query

The following method is invoked for a collection. It handles only integers:

def create_txrow( parti_id, paying_consumer_id, nation_vat_id )
  puts nation_vat_id
  puts nation_vat_id.class
  puts parti_id
  puts parti_id.class
      new_row = Txrow.create(
        nation_vat_id: nation_vat_id,
        paying_consumer_id: paying_consumer_id,
        parti_id: parti_id,
[...]

The console output returns as expected

1
Integer
2
Integer

Yet the log shows for each iteration of this method

 ↳ app/controllers/concerns/taxation_methods.rb:253:in `create_txrow'
  NationVat Load (0.5ms)  SELECT "nation_vats".* FROM "nation_vats" WHERE "nation_vats"."id" = $1 LIMIT $2  [["id", 1], ["LIMIT", 1]]
  ↳ app/controllers/concerns/taxation_methods.rb:253:in `create_txrow'
  Parti Load (0.6ms)  SELECT "partis".* FROM "partis" WHERE "partis"."id" = $1 LIMIT $2  [["id", 2], ["LIMIT", 1]]
  ↳ app/controllers/concerns/taxation_methods.rb:253:in `create_txrow'

Line 253 referes specifically to new_row = Txrow.create( line.

Thus these queries are being made to the database, but nothing in the code is requesting it... the integers should be nominally be fed to the method.

To avoid the N+1 problem, the collection is instantiated by a query that specifies
.includes( :parti, :shopvat in order to then select on the basis of the member of that collection
shopvat_for_item = shopvats.select{ |i| i.id = item.shopvat_id }.first and generate the call to this method with
new_txrow = create_txrow( item.parti_id, item.cover.consumer_id, shopvat_for_item.nation_vat_id).

What could possibly trigger two db queries (while not the third!)

Solution

These checks are for referential integrity. They ensure that the NationVat and the Parti exist based on the belongs_to relationship.

If you don't want this validation (which seems like a bad idea in this case) you can set optional: true on the belongs_to relationship.

class Txrow < ApplicationRecord
  belongs_to :nation_vat, optional: true
  belongs_to :parti, optional: true
end

Again given that Txrow seems to be an associative join between the NationVat and the Parti objects, I would not recommend making these optional but this will stop the queries you are seeing.