Transform entity / normalized response

Question

I wonder where is a good place to transform a response entity(ies) before it is set in my Redux state.

Example

• I have a chat_message entity
• It has a read boolean property sent by the server
• I need to compute a new unread boolean property = !message.read && message.user_id !== currentUser.id

Questions

1. Do I compute this new attribute in a getChatMessages selector (reselect)?
2. Do I compute this new attribute before I set the normalized response in my state? – Hence my question "Transform"
3. Do I just calculate it in my Component, but this (simple) logic is not shared and duplicated all over the place...
4. Do I send the unread attribute from the server...

Notes

• unread attribute example is a simplified example.
• I don't like solution 1., cause you need to share this logic between selectors anyway. So you might have a isMessageUnread helper function shared by getLastChatMessage, getChatMessages selectors. I also don't like selectors doing too much logic.
• I would lean towards solution 2. New unread attribute is computed only when receiving response.
• Solution 3. is my current lazy solution (with experiments here and there but nothing conclusive really)
• I don't like solution 4., these attributes are more UI-related than backend-related.
• If using solution 2., I feel like reducers is not a good place to do this tranformations. Might be easy for simple entities, but what about "heavy" transformation (iterating over collections, checking relationships, etc) ? I would prefer to put that new logic outside of: selectors, reducers, and entities. Kinda like a normalizr "plugin" / interceptor / transformer / post-processor...

Answer 1

Normalizr provides the processStrategy option:

Strategy to use when pre-processing the entity. Use this method to add extra data, defaults, and/or completely change the entity before normalization is complete.