Does updating one field will download the whole document from the database or just update local version?

问题

For example the document contains the following structure:

{
  fieldA: number,
  fieldB: {
    subFieldA: string,
    subFieldB: string,
  }
}

... and is being listened with the onSnapshot method.

FirebaseDb
  .collection(`someCollection`).doc('documentAbove')
  .onSnapshot({ includeMetadataChanges: true }, (snapshot) => {
    // when the document being modified it becomes available at this stage
  })

My question is if when the document will be modified will the firestore download it once again?

回答1:

Yes, the document will be downloaded again in its entirety while that listener is active, and you will be charged for a read on that document for each change.

来源：https://stackoverflow.com/questions/60315286/does-updating-one-field-will-download-the-whole-document-from-the-database-or-ju