<p align="center">
<img src="https://depeche-py.github.io/depeche-db/assets/logo-bg.png" width="200" />
</p>
# Depeche DB
A library for building event-based systems on top of PostgreSQL
[](https://github.com/depeche-py/depeche-db/actions/workflows/tests.yml)
[](https://pypi.python.org/pypi/depeche-db)
[](https://github.com/depeche-py/depeche-db)
[](https://depeche-py.github.io/depeche-db/)
[](https://github.com/depeche-py/depeche-db/blob/main/LICENSE)
---
**Documentation**: [https://depeche-py.github.io/depeche-db/](https://depeche-py.github.io/depeche-db/)
**Source code**: [https://github.com/depeche-py/depeche-db](https://github.com/depeche-py/depeche-db)
---
Depeche DB is modern Python library for building event-based systems
Key features:
* Message store with optimistic concurrency control & strong ordering guarantees
* Subscriptions with "at least once" semantics
* Parallel processing of (partitioned) subscriptions
* No database polling
## Requirements
Python 3.9+
SQLAlchemy 1.4 or 2+
PostgreSQL 12+
Psycopg (Version 2 >= 2.9.3 or Version 3 >= 3.1)
## Installation
```bash
pip install depeche-db
# OR
poetry add depeche-db
# OR
uv add depeche-db
```
## Example
```python
import pydantic, sqlalchemy, uuid, datetime as dt
from depeche_db import (
MessageStore,
StoredMessage,
MessageHandler,
SubscriptionMessage,
)
from depeche_db.tools import PydanticMessageSerializer
DB_DSN = "postgresql://depeche:depeche@localhost:4888/depeche_demo"
db_engine = sqlalchemy.create_engine(DB_DSN)
class MyMessage(pydantic.BaseModel):
content: int
message_id: uuid.UUID = pydantic.Field(default_factory=uuid.uuid4)
sent_at: dt.datetime = pydantic.Field(default_factory=dt.datetime.utcnow)
def get_message_id(self) -> uuid.UUID:
return self.message_id
def get_message_time(self) -> dt.datetime:
return self.sent_at
message_store = MessageStore[MyMessage](
name="example_store",
engine=db_engine,
serializer=PydanticMessageSerializer(MyMessage),
)
message_store.write(stream="aggregate-me-1", message=MyMessage(content=2))
print(list(message_store.read(stream="aggregate-me-1")))
# [StoredMessage(message_id=UUID('...'), stream='aggregate-me-1', version=1, message=MyMessage(content=2, message_id=UUID('...'), sent_at=datetime.datetime(...)), global_position=1)]
class ContentMessagePartitioner:
def get_partition(self, message: StoredMessage[MyMessage]) -> int:
return message.message.content % 10
class MyHandlers(MessageHandler[MyMessage]):
@MessageHandler.register
def handle_message(self, message: SubscriptionMessage[MyMessage]):
print(message)
aggregated_stream = message_store.aggregated_stream(
name="aggregated",
partitioner=ContentMessagePartitioner(),
stream_wildcards=["aggregate-me-%"],
)
subscription = aggregated_stream.subscription(
name="example_subscription",
handlers=MyHandlers(),
)
aggregated_stream.projector.run()
subscription.runner.run()
# MyHandlers.handle_message prints:
# SubscriptionMessage(partition=2, position=0, stored_message=StoredMessage(...))
```
## Contribute
Contributions in the form of issues, questions, feedback and pull requests are
welcome. Before investing a lot of time, let me know what you are up to so
we can see if your contribution fits the vision of the project.
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