Refactor AWS plugin and don't send excessive Exist: true attribute …

…to ensure an item with specified partition key exists

lib/dynamoid/adapter_plugin/aws_sdk_v3.rb

@@ -631,10 +631,7 @@ def expected_stanza(conditions = nil)
         conditions.delete(:unless_exists).try(:each) do |col|
           expected[col.to_s][:exists] = false
         end
-        conditions.delete(:if_exists).try(:each) do |col, val|
-          expected[col.to_s][:exists] = true
-          expected[col.to_s][:value] = val
-        end
+
         conditions.delete(:if).try(:each) do |col, val|
           expected[col.to_s][:value] = val
         end

lib/dynamoid/persistence/save.rb

@@ -89,8 +89,8 @@ def options_to_update_item
         end
 
         conditions = {}
-        conditions[:if_exists] ||= {}
-        conditions[:if_exists][@model.class.hash_key] = @model.hash_key
+        conditions[:if] ||= {}
+        conditions[:if][@model.class.hash_key] = @model.hash_key
 
         # Add an optimistic locking check if the lock_version column exists
         if @model.class.attributes[:lock_version]

lib/dynamoid/persistence/update_fields.rb

@@ -54,8 +54,8 @@ def options_to_update_item
         end
 
         conditions = @conditions.deep_dup
-        conditions[:if_exists] ||= {}
-        conditions[:if_exists][@model_class.hash_key] = @partition_key
+        conditions[:if] ||= {}
+        conditions[:if][@model_class.hash_key] = @partition_key
         options[:conditions] = conditions
 
         options