Fix migration to handle duplicate merchants per family

db/migrate/20250416235758_merchant_and_category_enrichment.rb

@@ -12,8 +12,34 @@ class MerchantAndCategoryEnrichment < ActiveRecord::Migration[7.2]
 
     reversible do |dir|
       dir.up do
-        # All of our existing merchants are family-generated right now
-        Merchant.update_all(type: "FamilyMerchant")
+        ActiveRecord::Base.transaction do
+          # 1) Mark all existing as FamilyMerchant
+          Merchant.update_all(type: "FamilyMerchant")
+
+          # 2) Find duplicate family merchants
+          Merchant
+            .where(type: 'FamilyMerchant')
+            .group(:family_id, :name)
+            .having("COUNT(*) > 1")
+            .pluck(:family_id, :name)
+            .each do |family_id, name|
+            # 3) Grab sorted IDs, first is keeper
+            ids, duplicate_ids = Merchant
+              .where(family_id: family_id, name: name)
+              .order(:id)
+              .pluck(:id)
+              .then { |arr| [ arr.first, arr.drop(1) ] }
+
+            next if duplicate_ids.empty?
+
+            # 4) Reassign all transactions pointing at the duplicates
+            Transaction.where(merchant_id: duplicate_ids)
+                       .update_all(merchant_id: ids)
+
+            # 5) Delete the duplicate merchant rows
+            Merchant.where(id: duplicate_ids).delete_all
+          end
+        end
       end
     end