Expressive URL-query to MongoDB query conversion library.

MoleQL allows your REST APIs or data layers to accept URL-style query strings (e.g. ?age>30&status=in(active,pending)) and converts them into MongoDB-compatible query dictionaries. It supports filters, sorting, skip/limit, projection and text search.

Example:

from moleql import parse

query = parse("age>30&country=US&name=/^John/i")
# yields:
# {
#   "filter": {"age": {"$gt": 30}, "country": "US", "name": {"$regex": "^John", "$options": "i"}},
#   "sort": None,
#   "skip": 0,
#   "limit": 0,
#   "projection": None
# }

• 🧠 Intuitive syntax: =, !=, <, <=, >, >=
• 📋 List operators: in(...), ...
• 🔍 Regex: /pattern/flags → $regex + $options
• 🧾 Pagination: skip=10, limit=50
• ⚙️ Sorting: sort=-created_at,name
• 🧩 Projection: fields=name,email,age
• 🔠 Text search: text=free text here or $text=free text here
• 🧱 Type casters: custom value transformations
• 🚫 Blacklist: skip parsing of restricted fields
• 🧪 Tested: full pytest coverage, Ruff linting

With uv (recommended):

uv add moleql

pip install moleql

from moleql import parse

query = parse("age>30&country=US&name=/^John/i")
print(query)

# {
#   "filter": {
#       "age": {"$gt": 30},
#       "country": "US",
#       "name": {"$regex": "^John", "$options": "i"}
#   },
#   "sort": None,
#   "skip": 0,
#   "limit": 0,
#   "projection": None
# }

Extended example

from moleql import parse

query = parse(
    "age>=18&status=in(active,pending)"
    "&sort=-created_at,name"
    "&skip=10&limit=20"
    "&fields=name,email,age"
)

Output:

{
    "filter": {
        "age": {"$gte": 18},
        "status": {"$in": ["active", "pending"]}
    },
    "sort": [("created_at", -1), ("name", 1)],
    "skip": 10,
    "limit": 20,
    "projection": {"name": 1, "email": 1, "age": 1}
}

parse(moleql_query: str, blacklist=None, casters=None) -> dict

from moleql import parse

parse("age>25&active=true")

Returns a dictionary with: filter, sort, skip, limit, projection

moleqularize(moleql_query: str, blacklist=None, casters=None) -> MoleQL

Parse a MoleQL string and return the internal MoleQL object for advanced inspection and debugging.

from moleql import moleqularize

m = moleqularize("age>25")
print(m.mongo_query)

You can define custom casters to control type conversions.

from moleql import parse, get_casters


def to_bool(value: str) -> bool:
    return value.lower() in ("true", "1", "yes")


custom_casters = {"bool": to_bool}

q = parse("active=bool(true)&age>30", casters=custom_casters)

• Transparency — The query string is readable and reversible.
• Safety — No eval, injection-safe parsing.
• Extensibility — Easy to plug in custom handlers.
• Predictability — Every operator maps 1:1 to Mongo semantics.
• Minimal dependencies — Pure Python, no ODM required.

FastAPI

from fastapi import FastAPI, Request
from moleql import parse
from pymongo import MongoClient

db = MongoClient()["app"]
app = FastAPI()


@app.get("/users")
def list_users(request: Request):
    q = parse(request.url.query.lstrip("?"))
    return list(db.users.find(q["filter"]))

Flask

from flask import Flask, request, jsonify
from moleql import parse

app = Flask(__name__)


@app.get("/orders")
def orders():
    q = parse(request.query_string.decode())
    return jsonify(q)

Run the full suite using uv:

uv sync --all-extras --dev
uv run pytest -vv --cov=moleql --cov-report=term-missing --cov-fail-under=100

Generate coverage:

uv run pytest --cov=moleql --cov-report=term-missing --cov-fail-under=100

This repository uses:

• Ruff — Linting + formatting (UP / pyupgrade rules)
• pre-commit — automatic checks
• pytest — testing
• uv — environment & packaging

Set up hooks:

uv run pre-commit install
uv run pre-commit run --all-files

• [] Add exists(field) and between(a,b) operators
• [] Add optional CLI (moleql "age>20" --as-json)
• [] Extended docs and tutorials

🤝 Contributing

1. Fork this repository

2. Create your feature branch

   git checkout -b feat/awesome-change

3. Run formatting and tests

   uv run pre-commit run --all-files
   uv run pytest

4. Commit and push your changes

5. Open a Pull Request 🚀

See CODE_OF_CONDUCT.md for details.

Built and maintained by @OneTesseractInMultiverse Inspired by the need for readable, typed, and safe Mongo queries in API environments.