previousData is lost when useLazyQuery's executor is called

Intended outcome: Extraneous calls of the callback returned by useLazyQuery should have no effect.

Actual outcome: Calling the callback always sets the previousData to undefined. To avoid this behaviour, the user has to keep track of “has the callback been called already?”

How to reproduce the issue: Here is a codesandbox which should demonstrate the issue in the console tab. There’s a variable you can tweak to enable/disable the workaround.

Versions

  System:
    OS: macOS 10.15.7
  Binaries:
    snip
  Browsers:
    Chrome: 87.0.4280.67
    Firefox: 80.0.1
    Safari: 14.0
  npmPackages:
    @apollo/client: ^3.3.1 => 3.3.1
    apollo: ^2.31.1 => 2.31.1

[tpict]

We’ve been thinking in AC4 of deprecating useLazyQuery(), insofar as it might just be easier to call the core client APIs directly in a useEffect when you need fine-grained control over when a query is made. Would that make people in this issue upset?

My initial thought is “no”, but could you give an example of what the useEffect callback would look like? I agree that the distinction between execute and refetch has always felt like a wart, but I get the impression that useLazyQuery is very widely used, so its removal might be upsetting to people if the replacement is much less ergonomic. Thanks for looking into this!

[hwillson]

This should now be resolved in @apollo/client@3.5.0. Let us know if you notice any issues. Thanks!