.document(uid) 和.whereEqual("uid", uid) 一样吗？

Question

Is this operation:

db.collection("users").document(uid)

The same with:

db.collection("users").whereEqual("uid", uid)

If a specific uid does not exist, are we still charged with a read operation? Is this available in both cases? Note, that the document is not created yet, there is nothing that can be read.

Answer 1

This code:

db.collection("users").document(uid)

Does not cost any document reads. No document has been read yet. The only thing it does is build a DocumentReference object that can be used to get() the document (or add a listener). The get() costs a document read.

This code:

db.collection("users").whereEqual("uid", uid)

Also does not cost a document read until you call get() (or add a listener). But if you do call get() , then it will always cost at least one document read, even if no document is present. This is covered in the documentation for pricing :

There is a minimum charge of one document read for each query that you perform, even if the query returns no results.