EF.Constant(keys) usage in BatchDataLoader does not work correctly (MSSQL EF8/9)

[kresimirlesic]

Product

Hot Chocolate

Version

14.1.0

Link to minimal reproduction

https://gist.github.com/kresimirlesic/32e39360f8ec10b6285f58721ec7d69c

Steps to reproduce

Invoke BatchDataLoader multiple times, passing down different values of keys.

What is expected?

Results from the database should match accordingly to the passed keys.

What is actually happening?

Incorrect results are being returned.
The constructed SQL contains keys in the query from the first BatchDataLoader invocation.

Relevant log output

Additional context

I did a bit of investigation on a side and the issue boils down to how HC reuses a list to populate the keys under the hood.
That causes a weird interaction with EF.

With list reusal:

Without list reusal:

[michaelstaib]

This is as designed. We by default rent a list for keys in DataLoader. If you want to use it in combination with EF.Constant you need to allocate a list that you can pass on by doing a ToList or ToArray on the keys.