pg_liquid

Create Your First Graph

This is the fastest way to learn the core pg_liquid model.

1. Assert Basic Facts

Graph facts are ordinary Liquid assertions:

select *
from liquid.query($$
  Edge("alice", "knows", "bob").
  Edge("bob", "knows", "carol").
  Edge(subject, predicate, object)?
$$) as t(subject text, predicate text, object text)
order by 1, 2, 3;

Each Edge(subject, predicate, object) assertion inserts one graph fact.

2. Query by Predicate

select *
from liquid.query($$
  Edge("alice", "knows", "bob").
  Edge("alice", "likes", "datalog").
  Edge("alice", predicate, object)?
$$) as t(predicate text, object text)
order by 1;

3. Ask a Reachability Question

Rules are query-local. They do not persist in the database.

select reachable
from liquid.query($$
  Edge("alice", "knows", "bob").
  Edge("bob", "knows", "carol").
  Edge("carol", "knows", "dana").

  Reach(x, y) :- Edge(x, "knows", y).
  Reach(x, z) :- Reach(x, y), Reach(y, z).

  Reach("alice", reachable)?
$$) as t(reachable text)
order by 1;

4. Use Variables and Anonymous Slots

Variables are bare identifiers. _ is anonymous.

select object
from liquid.query($$
  Edge("alice", "owns", "doc:1").
  Edge("alice", "owns", "doc:2").
  Edge("alice", "owns", object)?
$$) as t(object text)
order by 1;

5. Know the Mental Model

assertions before the final query are evaluated first
one terminal ? query returns rows
rules only exist for the duration of that call
graph storage is still PostgreSQL storage underneath

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