Current Data vs Data

[abhieshekumar]

I have been trying to understand the difference between currentData and data -

1. Is it that data will have the freshest copy while current data holds on the data provided in last successful fetch.
2. Also, if the later half is true does it also imply the current data is undefined only if the query has never resolved successfully.
3. I was trying to log currentData here, but couldn't see it. Please let me know if I have missed anything?

[markerikson]

Is it that data will have the freshest copy while current data holds on the data provided in last successful fetch.

Yep, this is it!

I was trying to log currentData here, but couldn't see it.

Looks like the sandbox is using RTK 1.6, and we added that in either 1.7 or 1.8. Bump the RTK version and it should be there.

[phryneas]

currentData is always bound exactly to the argument that is passed in, while data is trying to always have some value that you can display.
Most apps will probably only use data, in combination with some loading indicator or graying UI items out.
Does that make sense?

[wkigenyi]

Yes it makes sense.

[jtiret]

I've observed another distinction between data and currentData and am curious whether this behavior is intentional or a bug. Previously, I relied on data rather than currentData and frequently used api.util.updateQueryData for optimistic updates. I've noticed that when a query is in progress (e.g., triggered by polling), updates made via api.util.updateQueryData are not reflected in data, but are visible in currentData (even when I haven't altered the hook argument at all). This discrepancy isn't apparent when queries are fast, but with queries taking 200-300ms and a short polling interval, optimistic updates happening within this timeframe fail to apply.

[nostrapollo]

I've observed another distinction between data and currentData and am curious whether this behavior is intentional or a bug. Previously, I relied on data rather than currentData and frequently used api.util.updateQueryData for optimistic updates. I've noticed that when a query is in progress (e.g., triggered by polling), updates made via api.util.updateQueryData are not reflected in data, but are visible in currentData (even when I haven't altered the hook argument at all). This discrepancy isn't apparent when queries are fast, but with queries taking 200-300ms and a short polling interval, optimistic updates happening within this timeframe fail to apply.

@phryneas I'm looking at the same situation as explained in this comment above, before I create another issue/discussion I wanted to check if this is intended design or if there is a pattern to have data reflect changes to it's cache value before the request is completed. Let me know if this is better suited to a new issue, or more detail is required.

[phryneas]

I guess it should reflect those changes immediately. PRs and investigation would be very welcome.

[jukart]

I just found the following behaviour as problematic:

• we have a successful query result, which results in data and currentData to be the same and matching the query parameters
• now the query parameter is changed to skipToken, which results in data to stay as it was before and currentData change to undefined

I my opinion data should also be updated to undefined because this is the result of the current query (no result with skipToken).

[EskiMojo14]

data is the last successful result, undefined is not a successful result. Skipping doesn't necessarily mean you don't want to display the old data - and if it does, you have currentData and the status flags to decide that for yourself.