obj-db 1.1.2

Python binding for the obj embedded document database.

obj-db (Python)

The embedded document database for Python. Dependable. Portable. Zero-infrastructure.

Part of obj — a self-contained, serverless, single-file document database with a stable file format and full ACID semantics. The wheel is at parity with the Rust surface and writes a byte-identical file format.

Wheel obj-db on PyPI; import as obj. Built with PyO3 (abi3-py39).

pip install obj-db

---

Quickstart

Wrap a @dataclass with @obj.document for the typed, ergonomic API. The codec produces postcard bytes byte-identical to Rust's #[derive(Document)] for the same schema.

from dataclasses import dataclass
import obj

@obj.document(collection="orders", version=1)
@dataclass
class Order:
    customer_id: int
    total: float
    status: str

with obj.Db("app.obj") as db:
    doc_id = db.insert(Order(customer_id=1, total=99.5, status="pending"))
    order = db.get(Order, doc_id)
    for (oid, o) in db.all(Order):
        ...

---

Three write surfaces

The same CRUD methods (insert / get / update / upsert / delete / all) dispatch by argument type:

• Typed documents — pass an @obj.document instance or class. Routes through the schema-driven codec; on-disk bytes match Rust.
• Dict-native — pass a collection str plus a dict for ad-hoc writes with no @document boilerplate: db.insert("events", {...}).
• Raw bytes — pass a collection str plus bytes. obj does not serialise for you on this path; encode however you like (json, msgpack, postcard, pickle). Mirrors the obj C ABI contract.

db.update(Cls, id, fn) is an atomic read-modify-write inside one transaction (no lost-update window); a raising fn rolls it back. Per-document lazy migration mirrors Rust's Migrate trait via a history=[...] arg and a cls.migrate(doc, from_version) classmethod.

obj's encoding is positional (schema-driven, no field names in the bytes) and the schema registry is process-global per (collection, version). Two handles declaring the same collection with a different shape raise obj.InvalidArgumentError rather than risk a silent mis-encode — use distinct names or bump version=.

---

Transactions

WriteTxn batches many typed writes into a single commit / single WAL fsync, and reads see the transaction's own uncommitted writes:

with obj.Db("app.obj") as db:
    with db.transaction() as tx:
        for i in range(1000):
            tx.insert(Order(customer_id=i, total=float(i), status="new"))
        tx.update(Order, 1, lambda o: setattr(o, "status", "shipped"))
        tx.insert("audit_log", b"<raw bytes>")   # raw overload still works
        # one commit + one fsync on __exit__

tx.collection(Cls) binds a class once and exposes typed CRUD scoped to the transaction.

---

Secondary indexes

Declare indexes with typing.Annotated markers — obj.Index, obj.Unique, obj.Each (multi-value, on a list[...] field) — plus an indexes=[obj.Composite((...), name=...)] decorator arg. This mirrors Rust's #[obj(index ...)] attributes; the index B-trees are maintained on every write.

from typing import Annotated

@obj.document(
    collection="orders", version=1,
    indexes=[obj.Composite(("region", "status"), name="by_region_status")],
)
@dataclass
class Order:
    email:  Annotated[str, obj.Unique]      # unique index
    region: Annotated[str, obj.Index]       # standard index
    tags:   Annotated[list[str], obj.Each]  # multi-value index
    status: str = "new"

with obj.Db("app.obj") as db:
    db.insert(Order(email="[e-mail]", region="us", tags=["vip"]))
    order = db.find_unique(Order, "email", "[e-mail]")          # exact lookup
    for oid, o in db.index_range(Order, "region", "us", "us"): # half-open range
        ...

A duplicate Unique key raises obj.InvalidArgumentError and rolls the write back atomically.

---

Querying

db.query(...) returns a lazy, immutable builder (each call returns a fresh Query). Pass an @obj.document class for typed results or a collection str for dict-native results:

top = (db.query(Order)
         .filter(lambda o: o.status == "shipped")   # AND-combined predicates
         .sort_by(lambda o: o.total)
         .limit(10)
         .fetch())                                   # -> list[tuple[int, Order]]

count = db.query(Order).filter(lambda o: o.total > 100).count()  # no-decode fast path
us    = db.query(Order).index_range("region", "us", "us").fetch()

The sort buffer is bounded (obj.MAX_SORT_BUFFER, overridable per query with .sort_buffer_limit(n)); an over-cap sort raises rather than allocating without limit.

---

Multi-file attach

Open another .obj file's collections read-only under a namespace, addressed as "namespace.collection":

with obj.Db("app.obj") as db:
    db.attach("archive.obj", "archive")
    archived = list(db.all("archive.orders"))   # also db.get / db.query
    db.detach("archive")

Writes to a namespaced collection raise obj.InvalidArgumentError. A namespaced read needs its schema registered under the namespaced name (declare a class with collection="archive.orders", or read raw bytes); an unregistered read fails loud rather than returning garbage.

---

Async

obj.AsyncDb mirrors the blocking Db for asyncio callers — a thin wrapper that offloads each call to a thread executor (the GIL is released around engine work; no new runtime dependency).

import asyncio, obj

async def main():
    adb = await obj.AsyncDb.open("app.obj")
    oid = await adb.insert(Order(email="[e-mail]", region="us", tags=[]))
    async for oid, o in adb.all(Order):
        ...
    async with adb.transaction() as tx:      # commits on clean exit
        await tx.insert(Order(email="[e-mail]", region="eu", tags=[]))
    await adb.close()

asyncio.run(main())

Each async transaction pins one worker thread for its lifetime (the txn handle is not Send), so async with adb.transaction() is safe to drive op-by-op.

---

Checkpointing

Writes land in a write-ahead log (<db>.obj-wal) first; the main file stays sparse until a checkpoint folds committed WAL pages into it. A checkpoint fires automatically at ~1000 WAL frames, and a clean close() (including a with block that exits without raising) folds the WAL for you — so the .obj file is self-contained after normal shutdown.

with obj.Db("app.obj") as db:
    for note in notes:
        db.insert(note)
    db.checkpoint()   # fold on demand (optional)

checkpoint() is a no-op when there is nothing to fold, and is deferred if a concurrent reader has pinned a snapshot below the WAL end (retry once it finishes). The close-time fold is best-effort and non-fatal: a failure never turns a clean with block into a raised error, and an exit via exception skips the fold and propagates your error unchanged.

Trade-off: every clean close ends in an fsync. Prefer a single long-lived handle when one-fsync-per-close is a hot-path bottleneck.

---

Diagnostics

stat = db.stat()
for cs in stat.collections:
    print(cs.name, cs.doc_count, cs.file_size_bytes)
    for idx in cs.indexes:
        print(" ", idx.name, idx.kind, idx.key_paths, idx.status)

# low-level, type-erased dump of a collection's primary B-tree:
for rec in db.dump_raw("orders", max_records=1000):
    rec.id, rec.header, rec.payload   # id, DocumentHeader, raw postcard bytes

---

Exceptions

All operations raise instances of obj.ObjError (the catch-all base). The sub-exceptions narrow the diagnosis:

Exception	When raised
obj.NotFoundError	document / collection / index / namespace absent
obj.BusyError	lock contention (pager mutex, writer lock, cross-process)
obj.CorruptionError	on-disk format / checksum / B-tree invariant violation
obj.IntegrityError	Db.integrity_check() found at least one failure
obj.InvalidArgumentError	caller-side argument problem (encoding, range, type, schema)
obj.EncryptionError	missing / wrong / mismatched encryption key
obj.FeatureUnsupportedError	file uses a build-time feature this wheel lacks

---

Development

python3 -m venv .venv && source .venv/bin/activate
pip install maturin pytest

cd crates/obj-py
maturin develop          # build the cdylib + install editable into the venv
pytest tests/ -v

The dev loop is "edit Rust → maturin develop → pytest". For a release wheel: maturin build --release writes target/wheels/obj-*.whl.

---

License

Dual-licensed under MIT or Apache 2.0, at your option.