Support DocumentSnapshot cursors

[schmidt-sebastian]

The Python client should add support for DocumentSnapshot-based cursors.

See https://github.com/googleapis/java-firestore/blob/master/google-cloud-firestore/src/main/java/com/google/cloud/firestore/Query.java#L853 or https://github.com/googleapis/nodejs-firestore/blob/master/dev/src/reference.ts#L1663

[HemangChothani]

@schmidt-sebastian As per my research i think python supports DocumentSnapshot-based cursors, but the confusion is just because of naming convention, will update the name of the parameter so it could minimize the confusion.Let me know if i misunderstood anything or missing something.

python-firestore/google/cloud/firestore_v1/query.py

Line 460 in b1c5987

def start_at(self, document_fields):

python-firestore/google/cloud/firestore_v1/query.py

Lines 475 to 480 in b1c5987

	Args:
	document_fields
	(Union[:class:`~google.cloud.firestore_v1.document.DocumentSnapshot`, dict, list, tuple]):
	a document snapshot or a dictionary/list/tuple of fields
	representing a query results cursor. A cursor is a collection
	of values that represent a position in a query result set.

[schmidt-sebastian]

@HemangChothani Sorry, I missed this completely. Would it be possible to rename document_fields? That name caught my eyes and I immediately thought Python does not support these cursors.

The reason I looked at this was to figure out whether the Python SDK considers "IN" filters to be equality cursors. I am not able to decipher the code to provide an answer (

python-firestore/google/cloud/firestore_v1/query.py

Line 627 in b1c5987

if _has_snapshot_cursor:

). Only the operations GREATER_THAN, GREATER_THAN_OR_EQUALS, LESS_THAN or LESS_THAN_OR_EQUALS should be used to compute the implicit cursor. See also the fix here: googleapis/java-firestore#216. Do we need to port this fix?

[HemangChothani]

Would it be possible to rename document_fields?

@schmidt-sebastian Yes, I have opened a PR #58

Do we need to port this fix?

I think "IN" filter is not considered as a equality cursors. If i compare the python code it is similar to the old java code, but still need a conformation.

This line is not going to execute for == and array_contains operator.

python-firestore/google/cloud/firestore_v1/query.py

Lines 636 to 637 in b1c5987

	if filter_.op in should_order and field not in order_keys:
	orders.append(self._make_order(field, "ASCENDING"))

For better view i think need to concern @crwilcox

[HemangChothani]

@crwilcox Any suggestion on Python SDK considers "IN" filters to be equality cursors?

[HemangChothani]

@schmidt-sebastian I thinks this issue is resolved and only the operations GREATER_THAN, GREATER_THAN_OR_EQUALS, LESS_THAN or LESS_THAN_OR_EQUALS should be used to compute the implicit cursor.
As we can see here:

python-firestore/google/cloud/firestore_v1/base_query.py

Lines 682 to 689 in be98897

	if _has_snapshot_cursor:
	should_order = [
	_enum_from_op_string(key)
	for key in _COMPARISON_OPERATORS
	if key not in (_EQ_OP, "array_contains")
	]
	order_keys = [order.field.field_path for order in orders]
	for filter_ in self._field_filters:

so closing this issue for now, feel free to reopen if it doesn't fulfill the requirements.

[schmidt-sebastian]

Sounds good. Thanks for clarifying and sorry for the confusion.