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.

Answer 1

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.

Answer 2

There's nothing wrong in returned data by your queries because

var query1 = collection.where('key', isEqualTo: null);

In query1 basically you are running a query like - Select * from collection where 'key' = null and same in the query2.

And because bar has a key that has a null value your query1 is true and returning the data.

var query2 = collection.where('key', isNotEqualTo: null); 

And same scenario is happening with above query2 it also has a key that is not equals to `null. So it's also returning you the available data.

So because both of your where conditions are getting satisfied that's why they are returning you the available data.