Python gRPC Client for EventStoreDB

This package provides a Python gRPC client for EventStoreDB. It has been developed and tested to work with version 21.10 of EventStoreDB, and with Python versions 3.7, 3.8, 3.9, and 3.10.

Methods have typing annotations, the static typing is checked with mypy, and the test coverage is 100%.

Not all the features of the EventStoreDB API are presented by this client in its current form, however most of the useful aspects are presented in an easy-to-use interface (see below).

Installation

Use pip to install this package from the the Python Package Index.

$ pip install esdbclient

It is recommended to install Python packages into a Python virtual environment.

Getting started

Start EventStoreDB

Use Docker to run EventStoreDB from the official container image on DockerHub.

$ docker run -d --name my-eventstoredb -it -p 2113:2113 -p 1113:1113 eventstore/eventstore:21.10.2-buster-slim --insecure

Construct client

The class EsdbClient can be constructed with a uri that indicates the hostname and port number of the EventStoreDB server.

from esdbclient.client import EsdbClient

client = EsdbClient(uri='localhost:2113')

Append events

The method append_events() can be used to append events to a stream.

The arguments stream_name, expected_position and new_events are required.

The stream_name argument is a string that uniquely identifies the stream in the database.

The expected_position argument is an optional integer that specifies the expected position of the end of the stream in the database: either an integer representing the expected current position of the stream; or None if the stream is expected not to exist.

The events argument is a list of new event objects to be appended to the stream. The class NewEvent can be used to construct new event objects.

The method append_events() returns the "commit position", which is a monotonically increasing integer representing the position of the recorded event in a "total order" of all recorded events in all streams.

In the example below, a stream is created by appending a new event with expected_position=None.

from uuid import uuid4

from esdbclient.events import NewEvent

# Construct new event object.
event1 = NewEvent(type="OrderCreated", data=b"{}", metadata=b"{}")

# Define stream name.
stream_name1 = str(uuid4())

# Append list of events to new stream.
commit_position1 = client.append_events(
    stream_name=stream_name1, expected_position=None, events=[event1]
)

In the example below, two subsequent events are appended to an existing stream. Since the stream only has one recorded event, the current position of the end of the stream is 0.

event2 = NewEvent(type="OrderUpdated", data=b"{}", metadata=b"{}")
event3 = NewEvent(type="OrderDeleted", data=b"{}", metadata=b"{}")

commit_position2 = client.append_events(
    stream_name1, expected_position=0, events=[event2, event3]
)

Please note, whilst the appending in one operation of a list of events is atomic (either all or none will be recorded), by design it is only possible with EventStoreDB to atomically record events in one stream.

Read stream events

The method read_stream_events() can be used to read the recorded events in a stream. The argument stream_name is required. By default, all recorded events in the stream are returned in the order they were appended. An iterable object of recorded events is returned.

Read all the recorded events in a stream.

events = list(client.read_stream_events(stream_name=stream_name1))

assert len(events) == 3

assert events[0].stream_name == stream_name1
assert events[0].stream_position == 0
assert events[0].type == event1.type
assert events[0].data == event1.data

assert events[1].stream_name == stream_name1
assert events[1].stream_position == 1
assert events[1].type == event2.type
assert events[1].data == event2.data

assert events[2].stream_name == stream_name1
assert events[2].stream_position == 2
assert events[2].type == event3.type
assert events[2].data == event3.data

The method read_stream_events() also supports three optional arguments, position, backwards, and limit.

The argument position is an optional integer that can be used to indicate the stream position from which to start reading. This argument is None by default, meaning that the stream will be read from the start, or from the end if backwards is True.

The argument backwards is a boolean which is by default False meaning the stream will be read forwards by default, so that events are returned in the order they were appended, If backwards is True, the stream will be read backwards, so that events are returned in reverse order.

The argument limit is an integer which limits the number of events that will be returned.

Read recorded events in a stream from a specific stream position.

events = list(client.read_stream_events(stream_name1, position=1))

assert len(events) == 2

assert events[0].stream_name == stream_name1
assert events[0].stream_position == 1
assert events[0].type == event2.type
assert events[0].data == event2.data

assert events[1].stream_name == stream_name1
assert events[1].stream_position == 2
assert events[1].type == event3.type
assert events[1].data == event3.data

Read the recorded events in a stream backwards from the end.

events = list(client.read_stream_events(stream_name1, backwards=True))

assert len(events) == 3

assert events[0].stream_name == stream_name1
assert events[0].stream_position == 2
assert events[0].type == event3.type
assert events[0].data == event3.data

assert events[1].stream_name == stream_name1
assert events[1].stream_position == 1
assert events[1].type == event2.type
assert events[1].data == event2.data

Read a limited number of recorded events in stream.

events = list(client.read_stream_events(stream_name1, limit=2))

assert len(events) == 2

assert events[0].stream_name == stream_name1
assert events[0].stream_position == 0
assert events[0].type == event1.type
assert events[0].data == event1.data

assert events[1].stream_name == stream_name1
assert events[1].stream_position == 1
assert events[1].type == event2.type
assert events[1].data == event2.data

Read a limited number of recorded events backwards from given position.

events = list(client.read_stream_events(stream_name1, position=2, backwards=True, limit=1))

assert len(events) == 1

assert events[0].stream_name == stream_name1
assert events[0].stream_position == 2
assert events[0].type == event3.type
assert events[0].data == event3.data

Get current stream position

The method get_stream_position() can be used to get the current stream position of the last event in the stream.

current_position = client.get_stream_position(stream_name1)

assert current_position == 2

The sequence of stream positions is intended to be gapless. It is also usually zero-based, so that the position of the end of the stream when one event has been appended is 0. The position is 1 after two events have been appended, 2 after three events have been appended, and so on.

The position of a stream that does not exist is reported by this method to be None.

current_position = client.get_stream_position(stream_name="stream-unknown")

assert current_position == None

Read all recorded events

The method read_all_events() can be used to read all recorded events in all streams in the order they were committed. An iterable object of recorded events is returned.

Read events from all streams in the order they were committed.

events = list(client.read_all_events())

assert len(events) >= 3

The method read_stream_events() supports three optional arguments, position, backwards, and limit.

The argument position is an optional integer that can be used to indicate the commit position from which to start reading. This argument is None by default, meaning that all the events will be read from the start, or from the end if backwards is True. Please note, if given the commit position must be an actually existing commit position, and any other numbers will result in an exception being raised.

The argument backwards is a boolean which is by default False meaning all the events will be read forwards by default, so that events are returned in the order they were committed, If backwards is True, all the events will be read backwards, so that events are returned in reverse order.

The argument limit is an integer which limits the number of events that will be returned.

Please note, if backwards is used in combination with position, the recorded event at the given commit position will NOT be included. This differs from reading events from a stream backwards from a stream position, when the recorded event at the given stream position WILL be included.

Read recorded events in a stream from a particular position.

events = list(client.read_all_events(position=commit_position1))

assert len(events) == 3

assert events[0].stream_name == stream_name1
assert events[0].stream_position == 0
assert events[0].type == event1.type
assert events[0].data == event1.data

assert events[1].stream_name == stream_name1
assert events[1].stream_position == 1
assert events[1].type == event2.type
assert events[1].data == event2.data

assert events[2].stream_name == stream_name1
assert events[2].stream_position == 2
assert events[2].type == event3.type
assert events[2].data == event3.data

Read all the recorded events backwards from the end.

events = list(client.read_all_events(backwards=True))

assert len(events) >= 3

assert events[0].stream_name == stream_name1
assert events[0].stream_position == 2
assert events[0].type == event3.type
assert events[0].data == event3.data

assert events[1].stream_name == stream_name1
assert events[1].stream_position == 1
assert events[1].type == event2.type
assert events[1].data == event2.data

assert events[2].stream_name == stream_name1
assert events[2].stream_position == 0
assert events[2].type == event1.type
assert events[2].data == event1.data

Read a limited number of recorded events from a specific commit position.

events = list(client.read_all_events(position=commit_position1, limit=1))

assert len(events) == 1

assert events[0].stream_name == stream_name1
assert events[0].stream_position == 0
assert events[0].type == event1.type
assert events[0].data == event1.data

Read a limited number of recorded events backwards from the end.

events = list(client.read_all_events(backwards=True, limit=1))

assert len(events) == 1

assert events[0].stream_name == stream_name1
assert events[0].stream_position == 2
assert events[0].type == event3.type
assert events[0].data == event3.data

Catch-up subscriptions

The method subscribe_all_events() can be used to create a "catch-up subscription" to EventStoreDB. The optional argument position can be used to specify a commit position from which to receive recorded events. Please note, returned events are those after the given commit position.

This method returns an iterable object, a CatchupSubscription, from which recorded events can be obtained by iterating over the subscription object.

The recorded events can be processed. The commit position of the recorded event should be stored atomically with the results of processing the event. The value of the position argument can then be determined by reading the recorded commit position. This will accomplish "exactly once" processing of the events, from the point of view of the recorded results of processing the events, so long as there is a uniqueness constraint on the recorded commit position.

# Get the current commit position.
commit_position = client.get_commit_position()

# Append three more events.
stream_name = str(uuid4())
event1 = NewEvent(type="OrderCreated", data=b"", metadata=b"{}")
event2 = NewEvent(type="OrderUpdated", data=b"", metadata=b"{}")
event3 = NewEvent(type="OrderDeleted", data=b"", metadata=b"{}")
client.append_events(
    stream_name, expected_position=None, events=[event1, event2, event3]
)

# Subscribe from the last commit position.
subscription = client.subscribe_all_events(position=commit_position)

# Check the stream name of the newly received events.
events = []
for event in subscription:
    assert event.stream_name == stream_name
    events.append(event)
    if len(events) == 3:
        break

del subscription

The CatchupSubscription subscription object might be used within a thread, with recorded events put on a queue, for processing in a different thread. However, this client doesn't provide such a thing.

The NewEvent class

The NewEvent class can be used to define new events.

The attribute type is a unicode string, used to specify the type of the event to be recorded.

The attribute data is a byte string, used to specify the data of the event to be recorded.

The attribute metadata is a byte string, used to specify metadata for the event to be recorded.

new_event = NewEvent(
    type="OrderCreated",
    data=b"{}",
    metadata=b"{}",
)

The RecordedEvent class

The RecordedEvent class is used when reading recorded events.

The attribute type is a unicode string, used to indicate the type of the event that was recorded.

The attribute data is a byte string, used to specify the data of the event that was recorded.

The attribute metadata is a byte string, used to specify metadata for the event that was recorded.

The attribute stream_name is a unicode string, used to indicate the type of the name of the stream in which the event was recorded.

The attribute stream_position is an integer, used to indicate the position in the stream at which the event was recorded.

The attribute commit_position is an integer, used to indicate the position in total order of all recorded events at which the event was recorded.

from esdbclient.events import RecordedEvent

new_event = RecordedEvent(
    type="OrderCreated",
    data=b"{}",
    metadata=b"{}",
    stream_name="stream1",
    stream_position=0,
    commit_position=512,
)

Stop EventStoreDB

Use Docker to stop and remove the EventStoreDB container.

$ docker stop my-eventstoredb
$ docker rm my-eventstoredb

Developers

Clone the project repository, set up a virtual environment, and install dependencies.

Use your IDE (e.g. PyCharm) to open the project repository. Create a Poetry virtual environment, and then update packages.

$ make update-packages

Alternatively, use the make install command to create a dedicated Python virtual environment for this project.

$ make install

The make install command uses the build tool Poetry to create a dedicated Python virtual environment for this project, and installs popular development dependencies such as Black, isort and pytest.

Add tests in ./tests. Add code in ./esdbclient.

Start EventStoreDB.

$ make start-eventstoredb

Run tests.

$ make test

Stop EventStoreDB.

$ make stop-eventstoredb

Check the formatting of the code.

$ make lint

Reformat the code.

$ make fmt

Add dependencies in pyproject.toml and then update installed packages.

$ make update-packages