🐛 [firestore] Not able to filter/query on fields that are null

[puf]

Bug report

I have a query that tries to retrieve documents with a (date) field that has a null value.

const query = FirebaseFirestore.instance.collection("77468864").where("date", isEqualTo: null);
var snapshot = await query.get();
print('Got snapshot with ${snapshot.size} documents');

The Flutter code (when run on web, I didn't test other platforms) incorrectly returns documents with an actual date value, while the corresponding JavaScript code does not return these documents.

Steps to reproduce

0. I have a collection with one document that has two fields (date and string), both of which have a value.
1. Go to https://zapp.run/edit/firestore-query-null-date-zr1q06yyr1r0
2. Check the log output to see that the code returns a document with a non-null date field
3. Go to https://stackblitz.com/edit/firestore-v9-query-null-date?file=index.js
4. Check the log output to see that the code returns no documents

Expected behavior

I expect the Flutter and JavaScript projects to show the same result, given that they run an equivalent query on the same data.

---

Additional context

Originally reported here: https://stackoverflow.com/q/77468864

[Ehesp]

I believe there's a specific isNull named argument for this. The reason was that there's no concept of undefined in Dart, so it had to be specific when you want to filter by null

[puf]

Thanks Elliot!
I should've known this, especially since I'm pretty sure I used the isNull overload in the past.

Undefined and null are different concepts though. Why can't the Flutter wrapper recognize the null value that I used in my testbed: .where("date", isEqualTo: null)?

[danagbemava-nc]

Hi @puf, should this be treated as a feature request?

[russellwheatley]

Hey @puf, you have to use isNull named argument in the query because we check the value in queries here:

flutterfire/packages/cloud_firestore/cloud_firestore/lib/src/query.dart

Lines 658 to 659 in e51d2a2

	if (isEqualTo != null) addCondition(field, '==', isEqualTo);
	if (isNotEqualTo != null) addCondition(field, '!=', isNotEqualTo);

If the value is null, it does not become part of the query (as you can see in the link above). There really is no way around this as the API is currently implemented. We can't check whether the named arg was intentionally set as null by the user or unintentionally set (i.e. it is a nullable named argument).

Firestore doesn't allow undefined values set in the documents, the concept of undefined is a quirk of JavaScript and is not cross platform compatible as far as I'm aware.

[puf]

Thanks for clarifying Russel. Do any of our SDKs for other languages drop null values like that? Or is there something idiomatic Flutter about dropping null value?

[russellwheatley]

It is more an issue with the way the API was initially designed. In an ideal world, the operator and the value would be separate arguments. This would allow null values to be used on queries for isEqualTo & isNotEqualTo. But, because the operator and the value are set as one named argument, we cannot ascertain whether a null value was set by the user or not for that particular named argument (i.e. isEqualTo & isNotEqualTo).

[russellwheatley]

Hmmm, I've done a little bit of digging into this and there might be a way around it. I'll see what we can do 🤔

[Ehesp]

Could we make the default values of each argument a const/symbol which is internal, and if it's that value, skip it?

[russellwheatley]

@Ehesp We have a PR: #11896

We use a sentinel to check if the value was set by the user: https://github.com/firebase/flutterfire/pull/11896/files#diff-c388154c29616d9c4eff4b583681b56e75ae1f0291f6c31db037d3d1e85fdd65R9