Firestore Special Fields

To use the special Google Cloud Firestore server timestamp during creation, please use the special string __FIRESTORE_SERVER_TIMESTAMP__.

E.g., if you wanted to create a document with the field "created_at" the following syntax:
{"created_at": "__FIRESTORE_SERVER_TIMESTAMP__"}.
This will be converted to the firestore.SERVER_TIMESTAMP field

To use the special Google Cloud Firestore delete field command during updating, please use the special string __FIRESTORE_DELETE_FIELD__.

This will be converted to the firestore.DELETE_FIELD field