MonaDB

An embedded document store with Python dict semantics, built on redb. Documents are stored as BSON.

pip install monadb

import monadb

db = monadb.open("app.db")        # or monadb.open() for in-memory

db["users"]["alice"] = {"age": 30}
db["users"]["alice"]              # {"age": 30}
"alice" in db["users"]
len(db["users"])
del db["users"]["alice"]

Every operation is its own commit. update() is one commit for the whole mapping, so a bad item leaves nothing behind:

db["users"].update({"bob": {"age": 41}, "cy": {"age": 9}})

Ordered operations

Keys use an order-preserving encoding, so the b-tree's ordering is directly available:

events.range(start, stop)   # half-open [start, stop); None means unbounded
events.prefix("2026-08")    # str/bytes prefix, or a tuple of leading components
events.first(); events.last()
reversed(events)

Models

A collection is plain-dict by default and can be bound to a type. Binding is a property of the handle — nothing about the type is stored, so the same data is always readable as dicts.

from dataclasses import dataclass

@dataclass
class User:
    name: str
    age: int

users = db.collection("users", User)
users["alice"] = User(name="alice", age=30)
users["alice"]                    # User(name='alice', age=30)
db["users"]["alice"]              # {"name": "alice", "age": 30}

pydantic models work the same way, recognized by shape — MonaDB never imports pydantic.

How it differs from dict

  1. Iteration is key order, not insertion order.
  2. Keys are str | int | bytes | tuple of those. float, bool, and None raise TypeError; an int outside 64 bits raises ValueError.
  3. Values must be mappings — a dict, dataclass instance, or model.
  4. keys(), values(), items() are snapshot iterators, not live views.
  5. "a" and ("a",) are the same key — a scalar is a 1-component tuple.

Concurrency

Readers never block: redb is MVCC, so an open iterator keeps its own snapshot. Writers serialize — a second writer waits for the first to commit.

Only one process may open a database for writing. redb takes an exclusive file lock; several processes may open the same file read-only. This is the one capability 0.2 gives up relative to 0.1, which used LMDB.

Durability

durable=False trades commit durability for speed, which suits bulk loads:

db = monadb.open("app.db", durable=False)

Exceptions

monadb.Error covers storage faults and use of a closed database. Everything else is a Python builtin — KeyError, TypeError, ValueError.

Requirements

Python 3.9+. Building from source needs Rust 1.85+ (edition 2024).

Versions

0.2 is a rewrite. The SQL engine MonaDB shipped through 0.1 is preserved under the v0.1.0-sql git tag, and pip install "monadb<0.2" still installs it. Databases written by 0.1 cannot be read by 0.2.

License

Apache-2.0 — see LICENSE.

Project links

Data verified by PyPI on Aug 3, 2026
Data provided by the project maintainers, verified at the time the release was uploaded to PyPI.

Key dates

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Latest release

1 maintainer

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Avatar for robconhow from gravatar.com robconhow

Credits

Author: R. Conner Howell

GitHub Statistics

Data verified by PyPI on Aug 3, 2026
The GitHub source repository was provided by the project maintainers and verified by PyPI at the time of upload. Stars, forks, and open issues/PRs are derived from that repository and have not been independently verified.

License

Apache Software License (Apache-2.0)

Requires

Python >=3.9

Tags

database embedded document-store redb

Classifiers

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