Convert a Query instance to the corresponding protobuf.

    :type query: :class:`Query`
    :param query: The source query.

    :rtype: :class:`.query_pb2.Query`
    :returns: A protobuf that can be sent to the protobuf API.  N.b. that
              it does not contain "in-flight" fields for ongoing query
              executions (cursors, offset, limit).

def _pb_from_query(query):
    """Convert a Query instance to the corresponding protobuf.

    :type query: :class:`Query`
    :param query: The source query.

    :rtype: :class:`.query_pb2.Query`
    :returns: A protobuf that can be sent to the protobuf API.  N.b. that
              it does not contain "in-flight" fields for ongoing query
              executions (cursors, offset, limit).
    """
    pb = query_pb2.Query()

    for projection_name in query.projection:
        pb.projection.add().property.name = projection_name

    if query.kind:
        pb.kind.add().name = query.kind

    composite_filter = pb.filter.composite_filter
    composite_filter.op = query_pb2.CompositeFilter.AND

    if query.ancestor:
        ancestor_pb = query.ancestor.to_protobuf()

        # Filter on __key__ HAS_ANCESTOR == ancestor.
        ancestor_filter = composite_filter.filters.add().property_filter
        ancestor_filter.property.name = "__key__"
        ancestor_filter.op = query_pb2.PropertyFilter.HAS_ANCESTOR
        ancestor_filter.value.key_value.CopyFrom(ancestor_pb)

    for property_name, operator, value in query.filters:
        pb_op_enum = query.OPERATORS.get(operator)

        # Add the specific filter
        property_filter = composite_filter.filters.add().property_filter
        property_filter.property.name = property_name
        property_filter.op = pb_op_enum

        # Set the value to filter on based on the type.
        if property_name == "__key__":
            key_pb = value.to_protobuf()
            property_filter.value.key_value.CopyFrom(key_pb)
        else:
            helpers._set_protobuf_value(property_filter.value, value)

    if not composite_filter.filters:
        pb.ClearField("filter")

    for prop in query.order:
        property_order = pb.order.add()

        if prop.startswith("-"):
            property_order.property.name = prop[1:]
            property_order.direction = property_order.DESCENDING
        else:
            property_order.property.name = prop
            property_order.direction = property_order.ASCENDING

    for distinct_on_name in query.distinct_on:
        pb.distinct_on.add().name = distinct_on_name

    return pb