Query comparisons with null field

Question

My Firestore collection has documents with a string field, which can be null.

I was expecting that if I query:

Collection("products").Where("producedDate", "<", "2018-01-15")

I would get all products whose "producedDate" is earlier than "2018-10-15", including those whose "producedDate" is null.

But actually I am not getting the nulls.

Is this intended or it's a bug?

Answer 1

It was intended to work that way. The documentation states that:

When a query involves a field with values of mixed types, Cloud Firestore uses a deterministic ordering based on the internal representations. The following list shows the order:

1. Null values
2. Boolean values
3. Integer and floating-point values, sorted in numerical order
4. Date values
5. Text string values
6. [...]

Note that it only follows this order when you're running a query with values of mixed types. In your query you're passing a Date value, which means it will only query on values of Date type and not the others (like null for example).

In order to get the null values, you can create a compound query, by adding a second Where:

Collection("products").Where("producedDate", "<", "2018-01-15").Where("producedDate", "==", null)