Improve deprecation message for nested `where.not` condition

activerecord/lib/active_record/relation/query_methods.rb

@@ -52,7 +52,15 @@ def not(opts, *rest)
           ActiveSupport::Deprecation.warn(<<~MSG.squish)
             NOT conditions will no longer behave as NOR in Rails 6.1.
             To continue using NOR conditions, NOT each conditions manually
-            (`#{ opts.keys.map { |key| ".where.not(#{key.inspect} => ...)" }.join }`).
+            (`#{
+              opts.flat_map { |key, value|
+                if value.is_a?(Hash) && value.size > 1
+                  value.map { |k, v| ".where.not(#{key.inspect} => { #{k.inspect} => ... })" }
+                else
+                  ".where.not(#{key.inspect} => ...)"
+                end
+              }.join
+            }`).
           MSG
           @scope.where_clause += where_clause.invert(:nor)
         else

activerecord/test/cases/relation/where_test.rb

@@ -184,9 +184,14 @@ def test_where_not_polymorphic_id_and_type_as_nor_is_deprecated
     def test_where_not_association_as_nor_is_deprecated
       treasure = Treasure.create!(name: "my_treasure")
       PriceEstimate.create!(estimate_of: treasure, price: 2, currency: "USD")
-      PriceEstimate.create(estimate_of: treasure, price: 2, currency: "EUR")
+      PriceEstimate.create!(estimate_of: treasure, price: 2, currency: "EUR")
 
-      assert_deprecated do
+      message = <<~MSG.squish
+        NOT conditions will no longer behave as NOR in Rails 6.1.
+        To continue using NOR conditions, NOT each conditions manually
+        (`.where.not(:price_estimates => { :price => ... }).where.not(:price_estimates => { :currency => ... })`).
+      MSG
+      assert_deprecated(message) do
         result = Treasure.joins(:price_estimates).where.not(price_estimates: { price: 2, currency: "USD" })
 
         assert_predicate result, :empty?