According to

so since we cannot do x != null(I think this resulting in a runtime error) and not-in [...something, null] match nothing, is there any point using null in Firestore? or we should just avoid it and use the default value.

CodePudding user response：

so since we cannot do x != null

Yes, we can.

I think this results in a runtime error.

No, it doesn't.

Is there any point using null in Firestore?

Yes, you can query Firestore to get documents that contain a particular field that holds the value of null. Obviously, the opposite is available.

Edit:

not-in queries exclude documents where the given field does not exist.

It makes sense since Firestore queries can only return results based on the existence of a field and not on the absence.

A field exists when it's set to any value, including an empty string (""), null, and NaN (not a number).

Even if we add an empty string, null, or NaN, it doesn't mean that the field doesn't exist. It definitely exists and holds one of those values.

Note that x != null evaluates to undefined. A not-in query with null as one of the comparison values does not match any documents.

That's normal since a value from the list is null. You cannot compare null for non-null values.

CodePudding user response：

Note that x != null evaluates to undefined. A not-in query with null as one of the comparison values does not match any documents.

source https://firebase.google.com/docs/firestore/query-data/queries#not-in

there are 2 statements:

1. x != null evaluates undefined

2. A not-in query with null as one of the comparison values does not match any documents

I examine the statements one by one by running some tests

1. x != null evaluates undefined

this statement is false, it works fine, but probably because the sentences is not complete, it should be x != null evaluates undefined for non-exist field

2. A not-in query with null as one of the comparison values does not match any documents

this statement however, is true

where("x", "not-in", [null]) and where("x", "not-in", [...something, null]) will always return empty array even if there is document that fulfil the condition

there is however, a 3rd statement which is missing from the doc

where("x", "not-in", [...something]) will always exclude doc where x is null

update I discovered 4th behaviour

when null 1 data type, eg null string

x != something

will include doc where x is null

when there is more than 1 data type, eg null string number

x != something

will not include doc where x is null

so yeah, I would avoid null