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GFQL polars: LazyFrame node input crashes undirected single-hop Cypher (TypeError, not parity/NIE) #1740
Description
Activity
- added 5 commits that reference this issue
on Aug 13, 2026 Verified fixed on master
e6625ed28(post correctness-stack merge) — recommending close after review.Repro (issue's undirected single-hop with LazyFrame inputs), all four laziness combos:
import polars as pl, graphistry nodes_e = pl.DataFrame({"id": [1,2], "label__Person": [True, True]}) edges_e = pl.DataFrame({"src": [1], "dst": [2], "type": ["KNOWS"]}) Q = "MATCH (a:Person)-[:KNOWS]-(b) RETURN b.id AS x ORDER BY x" for tag, nn, ee in [("lazy nodes + eager edges", nodes_e.lazy(), edges_e), ("eager nodes + lazy edges", nodes_e, edges_e.lazy()), ("lazy both", nodes_e.lazy(), edges_e.lazy()), ("eager both", nodes_e, edges_e)]: g = graphistry.nodes(nn, "id").edges(ee, "src", "dst") f = g.gfql(Q, engine="polars")._nodes print(tag, sorted((f.collect() if isinstance(f, pl.LazyFrame) else f)["x"].to_list()))
Output on
e6625ed28(polars 1.42.0) — hand-computed expectation: undirected KNOWS from Person → x=[1,2]:lazy nodes + eager edges: OK -> [1, 2] eager nodes + lazy edges: OK -> [1, 2] lazy both: OK -> [1, 2] eager both: OK -> [1, 2]No
TypeErroron any mixed-laziness combination; all four return the correct answer. (A polarsPerformanceWarningabout LazyFrame schema resolution fires fromgraphistry/compute/filter_by_dict.py:75— cosmetic, not a correctness issue.)
Found by the #1737 seam re-review's input-type probes; pre-existing (the crash site is untouched by #1737's diff and predates it).
Repro
Matrix (undirected single-hop shape): lazy nodes + eager edges → crash; eager nodes + lazy edges → OK; lazy both → crash. Directed hops with LazyFrame inputs work fine.
Cause
_chain_traversal_polars's undirected single-hop node override (graphistry/compute/gfql/lazy/engine/polars/chain.py:~720):g._nodesis the user's LazyFrame while_bothis eager (or vice versa) — polars refuses mixed-laziness joins. UncaughtTypeErrorviolates the parity-or-honest-NIE contract (should be a correct result or an NIE, never a crash).Fix sketch
Normalize laziness at the join (
_both.lazy()wheng._nodesis a LazyFrame, or.lazy()both sides and keep the plan deferred). Add a lazy/eager input matrix test for the undirected shape.