Feature: support single-argument properties() function for Node, Rel, and Struct

[Mrhs121]

API

C++

Description

Summary

Add support for the openCypher / ISO GQL standard single-argument properties() function on NODE, REL, and STRUCT expressions (e.g., PROPERTIES(n) and PROPERTIES(r)).

---

Background & Motivation

Currently, Ladybug only supports the two-argument form of the PROPERTIES() function:

PROPERTIES(nodes(p), 'propName')

While this is useful for variable-length path property extraction, openCypher and other Cypher implementations (such as Neo4j and so on) standardly support a single-argument properties(entity):

MATCH (n:Person {name: 'Alice'})
RETURN properties(n);

Previously in Ladybug, calling properties(n) resulted in a binder error:

Binder exception: Function PROPERTIES did not receive correct arguments:
Actual:   (NODE)
Expected: (LIST,STRING) -> ANY

---

Key Use Cases

1. Clean Payloads for APIs / JSON Serialization: RETURN n returns graph entities containing internal system metadata (_ID, _LABEL). properties(n) extracts only clean user-defined business properties as a STRUCT.
2. First-class Expression Composition: Unlike n.* (which is a statement-level wildcard expansion and cannot be nested), properties(n) is a first-class expression that can be passed to aggregation functions like collect(properties(n)).
3. GraphRAG & LLM Prompt Construction: In Knowledge Graph / RAG pipelines, extracting clean entity/relationship property maps without system noise significantly reduces prompt token usage.

---

Proposed Behavior

• PROPERTIES(node: NODE) -> STRUCT: Returns a struct containing all user-defined properties of the node (excluding internal columns _ID, _LABEL).
• PROPERTIES(rel: REL) -> STRUCT: Returns a struct containing all user-defined properties of the relationship (excluding internal columns _ID, _LABEL, _SRC, _DST).
• PROPERTIES(struct: STRUCT) -> STRUCT: Returns the struct with user fields.
• PROPERTIES(list: LIST, prop: STRING) -> LIST: Existing two-argument form remains fully backwards compatible.

---

Example

CREATE NODE TABLE Person (name STRING, age INT64, city STRING, PRIMARY KEY (name));
CREATE (:Person {name: 'Alice', age: 25, city: 'Hangzhou'});

MATCH (n:Person {name: 'Alice'})
RETURN properties(n);
-- Output: {name: Alice, age: 25, city: Hangzhou}

MATCH (n:Person)
RETURN collect(properties(n)) AS all_users;
-- Output: [{name: Alice, age: 25, city: Hangzhou}]