feat: add IS_NOT_NULL operator to filters

[mgraczyk]

This allows filters like x.where("field", "!=", None) to work, matching the javascript implementation.

Also adds a test.

Fixes#970

[mgraczyk]

In addition to the unit test, I tested this against my production firestore database and it returns the expected results.

[mgraczyk]

Hi @daniel-sanche, would you mind taking a look or running the workflows? Should be a nice addition and bring the python sdk closer to feature parity with the Node sdk.

[vazome]

+1, I thought I'm tripping since I could do that in the console, but it's just GUI having more features than Python SDK, hehe.. heeeeeeee... after 4 years https://firebase.google.com/support/release-notes/js#version_7210_-_september_17_2020

[qaz10102030]

I hope this PR can be accepted as soon as possible. 🙏

[vazome]

Hey @daniel-sanche! Could you take a look?

[daniel-sanche]

This looks like a good addition, I will just have to check with other languages to make sure everything is consistent. I will also need to add some system tests before we can merge

Thanks for putting this together

[mgraczyk]

Just ran into this again today, would love if we could land this!

I'd be happy to write system tests are required to expedite

[mgraczyk]

Related but somewhat off topic, it would also be nice if we could refine the argument types for firestore.FieldFilter to more fail at type-checking time whenever the operands are known to be unsupported.

Even after my change there are gotchas passing None for comparison operators, and for transform sentinels like ArrayUnion and SERVER_TIMESTAMP

[mgraczyk]

@daniel-sanche I rebased on top of main

[daniel-sanche]

I'd be happy to write system tests are required to expedite

Unfortunately we are in a release freeze for the holidays, so we won't be able to cut a new release for this until early January. I will try to add some tests today

Thanks for your contributions, sorry about the delay in reviewing this!

[daniel-sanche]

There's a new security policy that our CI checks won't run against external forks, so it looks like I'll have to close this in favor of #988. We can continue discussion there. (I also added support for IS_NOT_NAN, which was also missing)

If you have any more contributions, I can pull them in manually from your fork, but I think we should be able to merge and release this when the freeze is over. Thanks again for putting this together!

Related but somewhat off topic, it would also be nice if we could refine the argument types for firestore.FieldFilter to more fail at type-checking time whenever the operands are known to be unsupported.

Even after my change there are gotchas passing None for comparison operators, and for transform sentinels like ArrayUnion and SERVER_TIMESTAMP

Feel free to open bugs for this, and let me know if you have a particular solution in mind. I'll take a look at this again in January