Dataset.quads() does not restrict results to specified graph

[edmondchuc]

I'm not sure if the following behaviour is expected or a bug in either Dataset/ConjunctiveGraph or the MemoryStore.

The test below shows that when iterating over quads from a specific graph, statements from other graphs leak into the result, except when using DATASET_DEFAULT_GRAPH_ID.

Only the third parameterized test (with DATASET_DEFAULT_GRAPH_ID) passes as expected. The first two tests (for named graphs urn:graph:a and urn:graph:b) incorrectly include statements from other graphs.

import pytest

from rdflib import RDF, SKOS, Dataset, Graph, Literal, URIRef
from rdflib.graph import DATASET_DEFAULT_GRAPH_ID


@pytest.mark.parametrize(
    "graph_name, expected_quads",
    [
        [
            URIRef("urn:graph:a"),
            {
                (
                    URIRef("http://example.com/s"),
                    RDF.type,
                    SKOS.Concept,
                    URIRef("urn:graph:a"),
                ),
                (
                    URIRef("http://example.com/s"),
                    SKOS.prefLabel,
                    Literal("Label"),
                    URIRef("urn:graph:a"),
                ),
            },
        ],
        [
            URIRef("urn:graph:b"),
            {
                (
                    URIRef("http://example.com/s"),
                    SKOS.prefLabel,
                    Literal("Label"),
                    URIRef("urn:graph:b"),
                ),
            },
        ],
        [
            DATASET_DEFAULT_GRAPH_ID,
            {
                (
                    URIRef("http://example.com/s"),
                    SKOS.definition,
                    Literal("Definition"),
                    DATASET_DEFAULT_GRAPH_ID,
                ),
            },
        ],
    ],
)
def test_mem_quads(
    graph_name: URIRef, expected_quads: set[tuple[URIRef, URIRef, Literal, URIRef]]
):
    data = f"""
        <http://example.com/s> <{RDF.type}> <{SKOS.Concept}> <urn:graph:a> .
        <http://example.com/s> <{SKOS.prefLabel}> "Label" <urn:graph:a> .
        <http://example.com/s> <{SKOS.prefLabel}> "Label" <urn:graph:b> .
        <http://example.com/s> <{SKOS.definition}> "Definition" .
    """
    ds = Dataset()
    ds..parse(data=data, format="nquads")
    quads = set(ds.quads((None, None, None, Graph(identifier=graph_name))))
    assert quads == expected_quads

Actual result when graph name is urn:graph:a:

Extra items in the left set:
  (rdflib.term.URIRef('http://example.com/s'), rdflib.term.URIRef('http://www.w3.org/2004/02/skos/core#prefLabel'), rdflib.term.Literal('Label'), rdflib.term.URIRef('urn:graph:b'))
  
  Full diff:
    {
        (
            rdflib.term.URIRef('http://example.com/s'),
            rdflib.term.URIRef('http://www.w3.org/1999/02/22-rdf-syntax-ns#type'),
            rdflib.term.URIRef('http://www.w3.org/2004/02/skos/core#Concept'),
            rdflib.term.URIRef('urn:graph:a'),
        ),
        (
            rdflib.term.URIRef('http://example.com/s'),
            rdflib.term.URIRef('http://www.w3.org/2004/02/skos/core#prefLabel'),
            rdflib.term.Literal('Label'),
            rdflib.term.URIRef('urn:graph:a'),
        ),
  +     (
  +         rdflib.term.URIRef('http://example.com/s'),
  +         rdflib.term.URIRef('http://www.w3.org/2004/02/skos/core#prefLabel'),
  +         rdflib.term.Literal('Label'),
  +         rdflib.term.URIRef('urn:graph:b'),
  +     ),
    }

Actual result when graph name is urn:graph:b:

Extra items in the left set:
  (rdflib.term.URIRef('http://example.com/s'), rdflib.term.URIRef('http://www.w3.org/2004/02/skos/core#prefLabel'), rdflib.term.Literal('Label'), rdflib.term.URIRef('urn:graph:a'))
  
  Full diff:
    {
  +     (
  +         rdflib.term.URIRef('http://example.com/s'),
  +         rdflib.term.URIRef('http://www.w3.org/2004/02/skos/core#prefLabel'),
  +         rdflib.term.Literal('Label'),
  +         rdflib.term.URIRef('urn:graph:a'),
  +     ),
        (
            rdflib.term.URIRef('http://example.com/s'),
            rdflib.term.URIRef('http://www.w3.org/2004/02/skos/core#prefLabel'),
            rdflib.term.Literal('Label'),
            rdflib.term.URIRef('urn:graph:b'),
        ),
    }

I tested this with RDFLib 7.4.0 as well as an older 7.0.0 and both had the same results.

[edmondchuc]

I think the following is what causes the leakage.

When looping through a graph A, if any triples in graph A exists in another graph B, the statement from graph B will leak.