jrgemignani opened a new pull request, #2441:
URL: https://github.com/apache/age/pull/2441
Add the feature create_subgraph() for materialized induced-subgraph
extraction.
Add ag_catalog.create_subgraph(new_graph, from_graph, node_filter,
relationship_filter) which materializes a new, persistent, fully
Cypher-queryable AGE graph as the induced subgraph of an existing graph.
Selection follows the graph-theory induced-subgraph definition as
operationalized by Neo4j GDS gds.graph.filter():
* a vertex is kept iff node_filter holds ('*' keeps all);
* an edge is kept iff relationship_filter holds AND both of its endpoints
were kept (no dangling edges).
Filters are arbitrary Cypher predicates bound to `n` (nodes) and `r`
(relationships) and are evaluated by AGE's own Cypher engine against the source
graph, so the full predicate language is available; label selection uses
label(n)/label(r) since the match pattern is fixed.
Implementation notes:
* Result is a real, ACID, registered graph (create_graph + create_v/
elabel), not a virtual view; it composes with cypher() and itself.
* Entity graphids are reassigned from the destination labels' own
sequences (graphid encodes a per-graph label id), and edge endpoints are
remapped through an old->new vertex map, enforcing the induced rule via inner
joins.
* Source label tables are read with FROM ONLY to avoid double-copying
children under PostgreSQL table inheritance.
* Properties of any agtype are preserved; self-loops and parallel edges
(multigraph structure) are retained.
* SECURITY INVOKER: reads respect the caller's table privileges and RLS;
the new graph is owned by the caller.
* Validates NULL/identical graph names, missing source, pre-existing
destination, and a reserved dollar-quote token in predicates.
Wire-up:
* sql/age_subgraph.sql (new) registered in sql/sql_files after
age_pg_upgrade; identical body added to age--1.7.0--y.y.y.sql so the
upgrade-path catalog comparison matches.
* regress/sql/subgraph.sql + expected output (new), added to REGRESS.
Covers full copy, vertex-induced, node+rel, label-only edge drop, bipartite,
empty result, composability, self-loops/parallel edges, property fidelity, and
error cases over a ~4500-vertex / 2000-edge source graph.
All 38 regression tests pass against PostgreSQL 18.
Co-authored-by: GitHub Copilot (Claude Opus 4.8) <[email protected]>
modified: Makefile
modified: age--1.7.0--y.y.y.sql
new file: regress/expected/subgraph.out
new file: regress/sql/subgraph.sql
new file: sql/age_subgraph.sql
modified: sql/sql_files
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