Bulk update OC variant changes in OC form

app/services/exchange_variant_bulk_updater.rb

@@ -0,0 +1,36 @@
+class ExchangeVariantBulkUpdater
+  def initialize(exchange)
+    @exchange = exchange
+  end
+
+  def update!(variant_ids)
+    sanitized_variant_ids = variant_ids.map(&:to_i).uniq
+    existing_variant_ids = @exchange.variant_ids
+
+    disassociate_variants!(existing_variant_ids - sanitized_variant_ids)
+    associate_variants!(sanitized_variant_ids - existing_variant_ids)
+
+    uncache_variant_associations
+  end
+
+  private
+
+  def disassociate_variants!(variant_ids)
+    return if variant_ids.blank?
+    @exchange.exchange_variants.where(variant_id: variant_ids).delete_all
+  end
+
+  def associate_variants!(variant_ids)
+    return if variant_ids.blank?
+
+    new_exchange_variants = variant_ids.map do |variant_id|
+      ExchangeVariant.new(exchange_id: @exchange.id, variant_id: variant_id)
+    end
+    ExchangeVariant.import!(new_exchange_variants)
+  end
+
+  def uncache_variant_associations
+    @exchange.exchange_variants.reset
+    @exchange.variants.proxy_association.reset
+  end
+end

lib/open_food_network/order_cycle_form_applicator.rb

@@ -66,10 +66,13 @@ module OpenFoodNetwork
 
     def add_exchange(sender_id, receiver_id, incoming, attrs = {})
       attrs = attrs.reverse_merge(sender_id: sender_id, receiver_id: receiver_id, incoming: incoming)
+      variant_ids = attrs.delete :variant_ids
       exchange = @order_cycle.exchanges.build attrs
 
       if manages_coordinator?
         exchange.save!
+        ExchangeVariantBulkUpdater.new(exchange).update!(variant_ids) unless variant_ids.nil?
+
         @touched_exchanges << exchange
       end
     end
@@ -85,7 +88,12 @@ module OpenFoodNetwork
       end
 
       if permission_for exchange
+        variant_ids = attrs.delete :variant_ids
+
         exchange.update_attributes!(attrs)
+
+        ExchangeVariantBulkUpdater.new(exchange).update!(variant_ids) unless variant_ids.nil?
+
         @touched_exchanges << exchange
       end
     end

spec/services/exchange_variant_bulk_updater_spec.rb

@@ -0,0 +1,43 @@
+require "spec_helper"
+
+describe ExchangeVariantBulkUpdater do
+  let!(:first_variant) { create(:variant) }
+  let!(:second_variant) { create(:variant) }
+  let!(:third_variant) { create(:variant) }
+
+  it "associates new variants to the exchange" do
+    exchange = create(:exchange)
+
+    described_class.new(exchange).update!([first_variant.id, second_variant.id])
+
+    # Check association cache.
+    expect(exchange.variants).to include(first_variant)
+    expect(exchange.variants).to include(second_variant)
+    # Check if changes are actually persisted.
+    exchange.reload
+    expect(exchange.variants).to include(first_variant)
+    expect(exchange.variants).to include(second_variant)
+  end
+
+  it "disassociates variants from the exchange" do
+    exchange = create(:exchange, variant_ids: [first_variant.id, second_variant.id])
+
+    described_class.new(exchange).update!([first_variant.id, third_variant.id])
+
+    # Check association cache.
+    expect(exchange.variants).to include(first_variant)
+    expect(exchange.variants).to include(third_variant)
+    # Check if changes are actually persisted.
+    exchange.reload
+    expect(exchange.variants).to include(first_variant)
+    expect(exchange.variants).to include(third_variant)
+
+    described_class.new(exchange).update!([])
+
+    # Check association cache.
+    expect(exchange.variants).to be_blank
+    # Check if changes are actually persisted.
+    exchange.reload
+    expect(exchange.variants).to be_blank
+  end
+end