WIP

metricflow/plan_conversion/node_processor.py

@@ -41,6 +41,7 @@ class MultiHopJoinCandidateLineage:
     to get the country dimension.
     """
 
+    # Lineage shows you the path to get to this join candidate?
     first_node_to_join: BaseOutput
     second_node_to_join: BaseOutput
     join_second_node_by_entity: LinklessEntitySpec
@@ -162,8 +163,11 @@ def _get_candidates_nodes_for_multi_hop(
             return ()
 
         multi_hop_join_candidates: List[MultiHopJoinCandidate] = []
-        logger.info(f"Creating nodes for {desired_linkable_spec}")
-
+        logger.info(f"Checking multi-hop join candidate nodes for for {desired_linkable_spec}")
+        # For all right nodes, loop through to see if they can be the first join of 2 hops.
+        # Then loop through them again to see which ones can be the second join of 2 hops.
+        # They must contain the proper entities, first off.
+        # Then check to see if they have the desired linkable specs.
         for first_node_that_could_be_joined in nodes:
             data_set_of_first_node_that_could_be_joined = self._node_data_set_resolver.get_output_data_set(
                 first_node_that_could_be_joined
@@ -211,6 +215,7 @@ def _get_candidates_nodes_for_multi_hop(
                 # The first and second nodes are joined by this entity
                 entity_reference_to_join_first_and_second_nodes = desired_linkable_spec.entity_links[1]
 
+                # Check for fan-out joins, skip if found.
                 if not self._join_evaluator.is_valid_instance_set_join(
                     left_instance_set=data_set_of_first_node_that_could_be_joined.instance_set,
                     right_instance_set=data_set_of_second_node_that_can_be_joined.instance_set,
@@ -219,11 +224,15 @@ def _get_candidates_nodes_for_multi_hop(
                     continue
 
                 # filter measures out of joinable_node
+                # Ok - so measures are never joined to the source node. They are from the source node.
                 specs = data_set_of_second_node_that_can_be_joined.instance_set.spec_set
                 filtered_joinable_node = FilterElementsNode(
                     parent_node=second_node_that_could_be_joined,
                     include_specs=InstanceSpecSet.from_specs(
-                        specs.dimension_specs + specs.entity_specs + specs.time_dimension_specs
+                        specs.dimension_specs
+                        + specs.entity_specs
+                        + specs.time_dimension_specs
+                        + specs.group_by_metric_specs  # add this!!!!
                     ),
                 )
 
@@ -286,10 +295,14 @@ def add_multi_hop_joins(
         lineage_for_all_multi_hop_join_candidates: Set[MultiHopJoinCandidateLineage] = set()
 
         for desired_linkable_spec in desired_linkable_specs:
+            # For each linkable spec, go thru available right nodes to see if they can satisfy this spec.
+            # next:
             for multi_hop_join_candidate in self._get_candidates_nodes_for_multi_hop(
                 desired_linkable_spec=desired_linkable_spec, nodes=nodes, join_type=join_type
             ):
                 # Dedupe candidates that are the same join.
+                # Why would they be the same join, but not the same node?
+                # We may never know. Oh well.
                 if multi_hop_join_candidate.lineage not in lineage_for_all_multi_hop_join_candidates:
                     all_multi_hop_join_candidates.append(multi_hop_join_candidate)
                     lineage_for_all_multi_hop_join_candidates.add(multi_hop_join_candidate.lineage)