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README.md

opencypher

OpenCypher AST and Builder API

OpenCypher defines an abstract syntax tree based on the published OpenCypher EBNF grammar and a builder-oriented API for constructing Cypher queries.

OpenCypher leans heavily on Python 3.7 dataclasses and typing.

Setup

pip install opencypher

Usage

The core API exposes a fluent builder interface for constructing queries and patterns:

from opencypher.api import match, node

query = match(
    node("person", "Person").rel_in().node("pet", "Pet")
).ret(
    "person",
    "pet",
)

print(query)  #  MATCH (person:Person)-[]->(pet :Pet) RETURN person, pet

The builder supports chaining patterns and chaining clauses; queries may terminate on either a return statement (.ret()) or on any updating clause (e.g. create(), delete(), merge(), and so forth.

from opencypher.api import match, node

query = match(
    node("alice", "Person", {"name": "Alice"}),
).match(
    node("bob", "Person", {"name": "Bob"}),
).merge(
    node("bob").rel_in(types="IS_FRIENDS_WITH").node("alice"),
).merge(
    node("alice").rel_in(types="IS_FRIENDS_WITH").node("bob"),
)

The resulting Cypher query object integrates with -- but does not depend on -- the Neo4J Python driver:

from neo4j import GraphDatabase

driver = GraphDatabase.driver("bolt://localhost:7687", auth=("neo4j", "password"))

with driver.session() as session:
    session.run(str(query), dict(query))

Caveats

Some compromises have been made with respect to the completeness of the AST:

  1. The grammar for expressions (and literals, atoms, etc.) has been deliberately simplified and reduces to str in many cases. The expression grammar is likely to get more complete over time.

  2. Some forms of argumementation (e.g. Set items) are not easy to construct using the builder API (although these remain available within the AST).

  3. Several top level query clauses are not yet implemented, including:

    • CALL
    • WITH
  4. Parameters do not automatically generate unique identifiers/prefixes. Parameter names will be derived from variable names where known, but no fallback exists yet for anonyomous pattern terms.

  5. Parameters do not support numeric values ($1); symbolic names ($foo) are supported.

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