Shortest Path

Where we left off

Traversal (Lessons 10-11) answers "what's reachable, and how far?" A different, equally common question is "what's the *shortest* way from here to there?" That's graph.shortest_path().

`graph.shortest_path()`

SELECT step, node_table_name, node_id, edge_label FROM graph.shortest_path(
  'public.people'::regclass, 'p4',
  'public.people'::regclass, 'p1',
  hydrate := false
);

Four required positional arguments: source table, source ID, target table, target ID. The result is the path itself, step by step, not just a distance.

What it actually returns, and why

Run the query above (Dan to Alice) and the path comes back through works_at, not reports_to, even though this course has been building toward a reporting-chain story:

step=0  people  p4
step=1  companies  c1  edge_label=works_at
step=2  people  p1  edge_label=works_at

Both paths (p4 -reports_to-> p2 -reports_to-> p1, and p4 -works_at-> c1 -works_at-> p1) are exactly two hops. graph.shortest_path() searches across *every* registered edge type by default and returns whichever shortest path it finds first, and unlike graph.traverse(), it takes no edge_types parameter to restrict that search. If you need a shortest path along one specific relationship only, you have two options: temporarily work with a graph that only has that edge type registered, or use graph.traverse() yourself and track the path by hand. This is a real, current limitation of the function, not a misunderstanding, worth knowing before you reach for it expecting graph.traverse()'s filtering options.