docs(firestore): on_snapshot document changes (#79)

* doc(firestore): change on_snapshot document

* doc(firestore): nit

* doc(firestore): change in example as not working

* doc(firestore): change in document snapshot example

Co-authored-by: HemangChothani <hemang.chothani@qlogic.io>

google/cloud/firestore_v1/collection.py

@@ -459,7 +459,8 @@ def on_snapshot(self, callback):
         provided callback is run on the snapshot of the documents.
 
         Args:
-            callback (Callable[[:class:`~google.cloud.firestore.collection.CollectionSnapshot`], NoneType]):
+            callback (Callable[List[:class:`~google.cloud.firestore_v1.collection.CollectionSnapshot`], \
+            List[:class:`~google.cloud.firestore_v1.watch.DocumentChange`], datetime.datetime], NoneType):
                 a callback to run when a change occurs.
 
         Example:
@@ -468,8 +469,8 @@ def on_snapshot(self, callback):
             db = firestore_v1.Client()
             collection_ref = db.collection(u'users')
 
-            def on_snapshot(collection_snapshot, changes, read_time):
-                for doc in collection_snapshot.documents:
+            def on_snapshot(docs, changes, read_time):
+                for doc in docs:
                     print(u'{} => {}'.format(doc.id, doc.to_dict()))
 
             # Watch this collection

google/cloud/firestore_v1/document.py

@@ -500,7 +500,8 @@ def on_snapshot(self, callback):
         provided callback is run on the snapshot.
 
         Args:
-            callback(Callable[[:class:`~google.cloud.firestore.document.DocumentSnapshot`], NoneType]):
+            callback (Callable[List[:class:`~google.cloud.firestore_v1.document.DocumentSnapshot`], \
+            List[:class:`~google.cloud.firestore_v1.watch.DocumentChange`], datetime.datetime], NoneType):
                 a callback to run when a change occurs
 
         Example:
@@ -512,9 +513,9 @@ def on_snapshot(self, callback):
             db = firestore_v1.Client()
             collection_ref = db.collection(u'users')
 
-            def on_snapshot(document_snapshot, changes, read_time):
-                doc = document_snapshot
-                print(u'{} => {}'.format(doc.id, doc.to_dict()))
+            def on_snapshot(docs, changes, read_time):
+                for doc in docs:
+                    print(u'{} => {}'.format(doc.id, doc.to_dict()))
 
             doc_ref = db.collection(u'users').document(
                 u'alovelace' + unique_resource_id())

google/cloud/firestore_v1/query.py

@@ -878,7 +878,8 @@ def on_snapshot(self, callback):
         provided callback is run on the snapshot of the documents.
 
         Args:
-            callback(Callable[[:class:`~google.cloud.firestore.query.QuerySnapshot`], NoneType]):
+            callback (Callable[List[:class:`~google.cloud.firestore_v1.query.QuerySnapshot`], \
+            List[:class:`~google.cloud.firestore_v1.watch.DocumentChange`], datetime.datetime], NoneType):
                 a callback to run when a change occurs.
 
         Example: