logicblocks.event.store

Eventing infrastructure for event sourced architectures.

Table of Contents

• Installation
• Usage
• Features
• Documentation
• Development
• Contributing
• License

Installation

pip install logicblocks.event.store

Usage

Basic Example

from logicblocks.event.store import EventStore, adapters
from logicblocks.event.types import NewEvent
from logicblocks.event.projection import Projector

adapter = adapters.InMemoryStorageAdapter()
store = EventStore(adapter)

stream = store.stream(category="profiles", stream="joe.bloggs")
stream.publish(
  events = [
    NewEvent(
      name="profile-created",
      payload={
        "name": "Joe Bloggs",
        "email": "joe.bloggs@example.com"
      }
    )
  ])
stream.publish(
  events = [
    NewEvent(
      name="date-of-birth-set",
      payload={
          "dob": "1992-07-10"
      }
    )
  ]
)

projector = Projector(
  handlers={
    "profile-created": lambda state, event: state.merge({
      "name": event.payload["name"],
      "email": event.payload["email"]
    }),
    "date-of-birth-set": lambda state, event: state.merge({
      "dob": event.payload["dob"]
    })
  }
)
profile = projector.project({}, stream.read())

# profile == {
#   "name": "Joe Bloggs", 
#   "email": "joe.bloggs@example.com", 
#   "dob": "1992-07-10"
# }

Features

• Event modelling:
  • Log / category / stream based: events are grouped into logs of categories of streams.
  • Arbitrary payloads and metadata: events can have arbitrary payloads and metadata limited only by what the underlying storage backend can support.
  • Bi-temporality support: events included timestamps for both the time the event was created and the time the event was recorded in the log.
• Event storage:
  • Immutable and append only: the event store is modelled as an append-only log of immutable events.
  • Consistency guarantees: concurrent stream updates can optionally be handled with optimistic concurrency control.
  • Write conditions: an extensible write condition system allows pre-conditions to be evaluated before publish.
  • Ordering guarantees: event writes are serialised (currently at log level) to guarantee consistent ordering at scan time.
  • Thread safety: the event store is thread safe and can be used in multithreaded applications.
• Storage adapters:
  • Storage adapter abstraction: adapters are provided for different storage backends, currently including:
    • an in-memory implementation for testing and experimentation; and
    • a PostgreSQL backed implementation for production use.
  • Extensible to other backends: the storage adapter abstract base class is designed to be relatively easily implemented to support other storage backends.
• Projections:
  • Reduction: event sequences can be reduced to a single value, a projection, using a projector.
  • Versioning: projections are versioned based on some attribute of the last event processed (position, sequence number, etc).
  • Storage: coming soon.
  • Snapshotting: coming soon.
• Types:
  • Type hints: includes type hints for all public classes and functions.
  • Value types: includes serialisable value types for identifiers, events and projections.
  • Pydantic support: coming soon.
• Testing utilities:
  • Builders: includes builders for events to simplify testing.
  • Data generators: includes random data generators for events and event attributes.
  • Storage adapter tests: includes tests for storage adapters to ensure consistency across implementations.

Documentation

• API docs

Development

To run the full pre-commit build:

./go

To run tests:

./go library:test:all          # all tests
./go library:test:unit         # unit tests
./go library:test:integration  # integration tests

To perform linting:

./go library:lint:check  # check linting rules are met
./go library:lint:fix    # attempt to fix linting issues

To format code:

./go library:format:check  # check code formatting
./go library:format:fix    # attempt to fix code formatting

To run type checking:

./go library:type:check  # check type hints

To build packages:

./go library:build

To see all available tasks:

./go -T

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/logicblocks/event.store. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.

License

Copyright © 2024 LogicBlocks Maintainers

Distributed under the terms of the MIT License.