Clone ExchangeVariant objects in bulk

An ExchangeVariant is a simple representation of a join table between Exchange and Variant. Previously this code was triggering an additional INSERT query for every variant added to the newly cloned exchange. Some exchanges have ~3000 variants! The code now creates them in bulk in a single INSERT statement. When cloning large order cycles this can improve performance by ~1000% or so.

app/models/exchange.rb

@@ -86,9 +86,9 @@ class Exchange < ApplicationRecord
     exchange = dup
     exchange.order_cycle = new_order_cycle
     exchange.enterprise_fee_ids = enterprise_fee_ids
-    exchange.variant_ids = variant_ids
     exchange.tag_ids = tag_ids
     exchange.save!
+    clone_all_exchange_variants(exchange.id)
     exchange
   end
 
@@ -105,4 +105,14 @@ class Exchange < ApplicationRecord
 
     receiver.touch_later
   end
+
+  private
+
+  def clone_all_exchange_variants(exchange_id)
+    return unless variant_ids.any?
+
+    ExchangeVariant.insert_all(
+      variant_ids.map{ |variant_id| { variant_id: variant_id, exchange_id: exchange_id } }
+    )
+  end
 end