Move connection-specific code

lib/fx/adapters/postgres.rb

@@ -125,7 +125,7 @@ def update_trigger(name, on:, sql_definition:)
       #
       # @return [void]
       def drop_function(name)
-        if support_drop_function_without_args
+        if connection.support_drop_function_without_args
           execute("DROP FUNCTION #{name};")
         else
           execute("DROP FUNCTION #{name}();")
@@ -154,14 +154,6 @@ def drop_trigger(name, on:)
       def connection
         Connection.new(connectable.connection)
       end
-
-      def support_drop_function_without_args
-        # https://www.postgresql.org/docs/9.6/sql-dropfunction.html
-        # https://www.postgresql.org/docs/10/sql-dropfunction.html
-
-        pg_connection = connectable.connection.raw_connection
-        pg_connection.server_version >= 10_00_00
-      end
     end
   end
 end

lib/fx/adapters/postgres/connection.rb

@@ -1,8 +1,27 @@
 module Fx
   module Adapters
     class Postgres
+      # Decorates an ActiveRecord connection with methods that help determine
+      # the connections capabilities.
+      #
+      # Every attempt is made to use the versions of these methods defined by
+      # Rails where they are available and public before falling back to our own
+      # implementations for older Rails versions.
+      #
       # @api private
       class Connection < SimpleDelegator
+        # https://www.postgresql.org/docs/9.6/sql-dropfunction.html
+        # https://www.postgresql.org/docs/10/sql-dropfunction.html
+        def support_drop_function_without_args
+          pg_connection = undecorated_connection.raw_connection
+          pg_connection.server_version >= 10_00_00
+        end
+
+        private
+
+        def undecorated_connection
+          __getobj__
+        end
       end
     end
   end