Firestore null query returns non-nullable field

Question

var collection = FirebaseFirestore.instance.collection('foo');
var query1 = collection.where('key', isEqualTo: null);
var query2 = collection.where('key', isNotEqualTo: null); 

Both query1 and query2 returns bar and baz documents. But according to my understanding, query1 should have returned bar only.

Solution 1

FlutterFire member here:

Doing isEqualTo: null is not supported. It is behaving as if you did where('key'), aka doing nothing.

As 呂學洲 mentioned, it is required to use isNull: true

Solution 2

You should use isNull instead.

query.where(key, isNull: true); //bar
query.where(key, isNull: false); //baz

I can't find any document describing why things implemented this way. But I'm guessing that sending isEqualTo/isNotEqualTo with null is telling Firestore to get documents that exist the field.

You can try querying document bak which doesn't have field key.

Comments

[Dharmaraj]

I wasn't able to replicate this issue. This could be something with Flutter SDK then. Javascript SDK worked fine for me.

[iDecode]

But if you remove key from bar, then also it returns the same results.

[iDecode]

I knew isNull part, and it works as intended but the question was why isEqualTo: null also returning "value" documents. Even if there's no key, both isEqualTo and isNotEqualTo returns same documents. If no answer is provided to my exact question, then I'll accept yours (although I already knew this thing)

[Diwyansh]

can you add that to your question as well?

[iDecode]

I'm sure you must have tested your code before writing the answer, so in your sample you can remove key and see it returning the same results.

[iDecode]

Thanks, but can you point me to the docs where it says "isEqualTo: null" is not supported, I must have missed it.

[Rémi Rousselet]

I doubt there's docs about that. It's about how Dart and where works. Since Dart has no undefined, doing isEqualTo:null is identical to not passing it

[iDecode]

Ok, that made sense. I'm accepting your answer but will award the bounty to another user as he mentioned the working solution before you ;)