omnigraph/docs/user/query-language.md

Query Language (.gq)

Pest grammar at crates/omnigraph-compiler/src/query/query.pest. AST in query/ast.rs. Type checker in query/typecheck.rs. Lowering in ir/lower.rs.

Query declarations

query <name>($p1: T1, $p2: T2?, …)
  @description("…") @instruction("…") {
  …
}

Two body shapes:

• Read: match { … } return { … } [order { … }] [limit N]
• Mutation: one or more of insert | update | delete statements

Param types reuse all schema scalars; trailing ? makes a param optional. The compiler reserves $__nanograph_now for now().

MATCH clauses

• Binding: $x: NodeType { prop: <literal | $param | now()>, … }
• Traversal: $src EDGE_NAME { min, max? } $dst — variable-length paths via hop bounds; default 1..1 if bounds omitted.
• Filter: <expr> <op> <expr> with operators >=, <=, !=, >, <, =, and string contains.
• Negation: not { clause+ } — desugars to anti-join over the inner pipeline.

Search clauses (multi-modal)

Used inside MATCH or as expressions inside RETURN/ORDER:

Function	Purpose	Underlying Lance facility
nearest($x.vec, $q)	k-NN vector search (cosine)	Lance vector index (IVF / HNSW)
search(field, q)	Generic FTS	Inverted index
fuzzy(field, q [, max_edits])	Levenshtein-tolerant text search	Inverted index
match_text(field, q)	Pattern match	Inverted index
bm25(field, q)	BM25 scoring	Inverted index
rrf(rank_a, rank_b [, k])	Reciprocal Rank Fusion of two rankings (default k=60)	OmniGraph fuses scored rankings

nearest() requires a LIMIT; the compiler resolves the query vector via the param map (or via the runtime embedding client when bound to a text input).

RETURN clause

return { <expr> [as <alias>], … } with expressions:

• Variable / property access: $x, $x.prop
• Literals: string, int, float, bool, list
• now()
• Aggregates: count, sum, avg, min, max
• All search functions above (so you can return a score column)
• AliasRef — re-use a previous projection alias

ORDER & LIMIT

• order { <expr> [asc|desc], … } — supports plain expressions and nearest(...).
• limit <integer> — required when there is a nearest(...) ordering.

Mutation statements

• insert <Type> { prop: <value>, … }
• update <Type> set { prop: <value>, … } where <prop> <op> <value>
• delete <Type> where <prop> <op> <value>

<value> is a literal, $param, or now(). Multi-statement mutations execute atomically (added in v0.2.0).

D₂ — mixed insert/update + delete is rejected at parse time

A single mutation query must be either insert/update-only or delete-only. Mixed → rejected before any I/O with the message:

mutation '<name>' on the same query mixes inserts/updates and deletes; split into separate mutations: (1) inserts and updates, then (2) deletes. This restriction lifts when Lance exposes a two-phase delete API (tracked: MR-793 / Lance-upstream).

Reason: under the staged-write rewire (MR-794), inserts and updates accumulate in memory and commit at end-of-query, while deletes still inline-commit (Lance 4.0.0 has no public two-phase delete). Mixing creates ordering hazards (same-row insert→delete becomes a no-op because the staged insert isn't visible to delete; cascading deletes of just-inserted edges break referential integrity by silent design). Until Lance exposes DeleteJob::execute_uncommitted, the parse-time rejection keeps both paths atomic and correct. See docs/dev/writes.md and docs/dev/invariants.md.

IR (Intermediate Representation)

QueryIR { name, params, pipeline: Vec<IROp>, return_exprs, order_by, limit }

Pipeline operations:

• NodeScan { variable, type_name, filters }
• Expand { src_var, dst_var, edge_type, direction (Out|In), dst_type, min_hops, max_hops, dst_filters } — destination filters are pushed into the expand so Lance scalar pushdown can prune. Executed one of two ways, chosen per-expand by a cost model over cheap manifest counts (frontier size, |E|, source-vertex count, hops) plus index coverage: selective traversals (small frontier relative to the source set) resolve neighbors from the persisted src/dst BTREE (one indexed scan per hop, cost ∝ frontier); dense / deep / large-frontier traversals — or those whose BTREE coverage is degraded so a full scan would be paid per hop — use the in-memory CSR adjacency index. Both produce identical results. Bounded by OMNIGRAPH_EXPAND_INDEXED_MAX_FRONTIER / OMNIGRAPH_EXPAND_INDEXED_MAX_HOPS (hard ceilings, beyond which CSR is always used), with OMNIGRAPH_TRAVERSAL_MODE=indexed|csr forcing a mode (see constants).
• Filter { left, op, right }
• AntiJoin { outer_var, inner: Vec<IROp> } — for not { … }

Lowering:

1. Partition MATCH clauses (bindings, traversals, filters, negations).
2. Identify "deferred" bindings (a destination of a traversal that has filters) so the Expand can carry the filter as a pushdown.
3. Emit NodeScan for the first binding, then Expand operations, then remaining Filter operations, then AntiJoins for negations.
4. Translate RETURN / ORDER expressions; preserve LIMIT.

Linting & validation (query/lint.rs)

Codes seen so far:

• Q000 (Error): parse error
• L201 (Warning): nullable property never set by any UPDATE — "{type}.{prop} exists in schema but no update query sets it"
• (Warning): mutation declares no params — hardcoded mutations are easy to miss
• Plus all type errors from typecheck_query_decl() (undefined types, mismatched operators, undefined edges, etc.)

Output:

QueryLintOutput { status, schema_source, query_path,
  queries_processed, errors, warnings, infos,
  results: [{ name, kind, status, error?, warnings[] }],
  findings: [{ severity, code, message, type_name?, property?, query_names[] }] }

CLI exits non-zero only on status = Error.