From 3249b14557f795568b7f62d22a8305a3c7e40b04 Mon Sep 17 00:00:00 2001 From: Ashutosh Bapat Date: Fri, 19 Jun 2026 17:06:29 +0530 Subject: [PATCH v20260619 01/11] Prevent dropping the last label from a property graph element Per SQL/PGQ standard, every graph element must have at least one label. When dropping a label from a graph element, ensure that there exists at least one other label on the element. If the label being dropped is the only label on the element, raise an error. We hold an exclusive lock when modifying a property graph. Hence the label will not be dropped even when multiple labels are being dropped concurrently. Reported By: Satyanarayana Narlapuram Author: Ashutosh Bapat Author: Satyanarayana Narlapuram Reviewed by: Ashutosh Bapat Discussion: https://www.postgresql.org/message-id/CAHg+QDeP=mTHTV48R23zKMy1SBmCKZ_L7-z5zKnYyw+K0x-gCg@mail.gmail.com --- doc/src/sgml/ref/alter_property_graph.sgml | 4 +- src/backend/commands/propgraphcmds.c | 52 +++++++++++++++++-- .../expected/create_property_graph.out | 7 +++ .../regress/sql/create_property_graph.sql | 5 ++ 4 files changed, 62 insertions(+), 6 deletions(-) diff --git a/doc/src/sgml/ref/alter_property_graph.sgml b/doc/src/sgml/ref/alter_property_graph.sgml index f517f2b2d7a..2fd0c138e12 100644 --- a/doc/src/sgml/ref/alter_property_graph.sgml +++ b/doc/src/sgml/ref/alter_property_graph.sgml @@ -99,7 +99,9 @@ ALTER PROPERTY GRAPH [ IF EXISTS ] nameALTER {VERTEX|NODE|EDGE|RELATIONSHIP} TABLE ... DROP LABEL - This form removes a label from an existing vertex or edge table. + This form removes a label from an existing vertex or edge table. The + last label on an element table cannot be dropped; every vertex or edge + table must have at least one label. diff --git a/src/backend/commands/propgraphcmds.c b/src/backend/commands/propgraphcmds.c index cc516e27020..62f91a08410 100644 --- a/src/backend/commands/propgraphcmds.c +++ b/src/backend/commands/propgraphcmds.c @@ -1491,8 +1491,14 @@ AlterPropGraph(ParseState *pstate, const AlterPropGraphStmt *stmt) { Oid peoid; Oid labeloid; - Oid ellabeloid; + Oid ellabeloid = InvalidOid; ObjectAddress obj; + Relation ellabelrel; + SysScanDesc ellabelscan; + ScanKeyData ellabelkey[1]; + int nlabels; + HeapTuple tuple; + if (stmt->element_kind == PROPGRAPH_ELEMENT_KIND_VERTEX) peoid = get_vertex_oid(pstate, pgrelid, stmt->element_alias, -1); @@ -1510,10 +1516,35 @@ AlterPropGraph(ParseState *pstate, const AlterPropGraphStmt *stmt) get_rel_name(pgrelid), stmt->element_alias, stmt->drop_label), parser_errposition(pstate, -1)); - ellabeloid = GetSysCacheOid2(PROPGRAPHELEMENTLABELELEMENTLABEL, - Anum_pg_propgraph_element_label_oid, - ObjectIdGetDatum(peoid), - ObjectIdGetDatum(labeloid)); + /* + * Is the given label associated with the element? Is this the only + * label associated with the element? Scan the + * pg_propgraph_element_label table to find answers to these + * questions. Stop scanning midway when both answers come out to be + * "yes". + */ + ellabelrel = table_open(PropgraphElementLabelRelationId, AccessShareLock); + ScanKeyInit(&ellabelkey[0], + Anum_pg_propgraph_element_label_pgelelid, + BTEqualStrategyNumber, F_OIDEQ, + ObjectIdGetDatum(peoid)); + ellabelscan = systable_beginscan(ellabelrel, PropgraphElementLabelElementLabelIndexId, + true, NULL, 1, ellabelkey); + nlabels = 0; + while (HeapTupleIsValid(tuple = systable_getnext(ellabelscan))) + { + Form_pg_propgraph_element_label ellabelform = (Form_pg_propgraph_element_label) GETSTRUCT(tuple); + + nlabels++; + + if (ellabelform->pgellabelid == labeloid) + ellabeloid = ellabelform->oid; + + if (nlabels > 1 && ellabeloid) + break; + } + systable_endscan(ellabelscan); + table_close(ellabelrel, AccessShareLock); if (!ellabeloid) ereport(ERROR, @@ -1522,6 +1553,17 @@ AlterPropGraph(ParseState *pstate, const AlterPropGraphStmt *stmt) get_rel_name(pgrelid), stmt->element_alias, stmt->drop_label), parser_errposition(pstate, -1)); + /* + * Prevent dropping the last label from an element. Every element must + * have at least one label associated with it. + */ + if (nlabels == 1) + ereport(ERROR, + (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE), + errmsg("cannot drop the last label from element \"%s\"", + stmt->element_alias), + errhint("Every element must have at least one label."))); + ObjectAddressSet(obj, PropgraphElementLabelRelationId, ellabeloid); performDeletion(&obj, stmt->drop_behavior, 0); diff --git a/src/test/regress/expected/create_property_graph.out b/src/test/regress/expected/create_property_graph.out index 86c0957dcc7..e074c3cbd69 100644 --- a/src/test/regress/expected/create_property_graph.out +++ b/src/test/regress/expected/create_property_graph.out @@ -57,6 +57,13 @@ ALTER PROPERTY GRAPH g3 ALTER PROPERTY GRAPH g3 ALTER VERTEX TABLE t3 DROP LABEL t3l3x; -- error ERROR: property graph "g3" element "t3" has no label "t3l3x" ALTER PROPERTY GRAPH g3 ALTER VERTEX TABLE t3 DROP LABEL t3l3; +-- Test that the last label on an element cannot be dropped +ALTER PROPERTY GRAPH g3 ALTER VERTEX TABLE t3 DROP LABEL t3l2; +ALTER PROPERTY GRAPH g3 ALTER VERTEX TABLE t3 DROP LABEL t3l1; -- error: last label +ERROR: cannot drop the last label from element "t3" +HINT: Every element must have at least one label. +-- Restore the dropped label for further tests +ALTER PROPERTY GRAPH g3 ALTER VERTEX TABLE t3 ADD LABEL t3l2 PROPERTIES ALL COLUMNS; ALTER PROPERTY GRAPH g3 DROP VERTEX TABLES (t2); -- fail ERROR: cannot drop vertex t2 of property graph g3 because other objects depend on it DETAIL: edge e1 of property graph g3 depends on vertex t2 of property graph g3 diff --git a/src/test/regress/sql/create_property_graph.sql b/src/test/regress/sql/create_property_graph.sql index 85088ae632c..b10d7191506 100644 --- a/src/test/regress/sql/create_property_graph.sql +++ b/src/test/regress/sql/create_property_graph.sql @@ -52,6 +52,11 @@ ALTER PROPERTY GRAPH g3 ADD LABEL t3l3 PROPERTIES ALL COLUMNS; ALTER PROPERTY GRAPH g3 ALTER VERTEX TABLE t3 DROP LABEL t3l3x; -- error ALTER PROPERTY GRAPH g3 ALTER VERTEX TABLE t3 DROP LABEL t3l3; +-- Test that the last label on an element cannot be dropped +ALTER PROPERTY GRAPH g3 ALTER VERTEX TABLE t3 DROP LABEL t3l2; +ALTER PROPERTY GRAPH g3 ALTER VERTEX TABLE t3 DROP LABEL t3l1; -- error: last label +-- Restore the dropped label for further tests +ALTER PROPERTY GRAPH g3 ALTER VERTEX TABLE t3 ADD LABEL t3l2 PROPERTIES ALL COLUMNS; ALTER PROPERTY GRAPH g3 DROP VERTEX TABLES (t2); -- fail ALTER PROPERTY GRAPH g3 DROP VERTEX TABLES (t2) CASCADE; ALTER PROPERTY GRAPH g3 DROP EDGE TABLES (e2); base-commit: dc5116780846951a409d788479a9e9fa6edd9f07 -- 2.34.1