Spear EventStoreDB adapter for Commanded

Commanded EvenstoreDB adapter based on spear. The code is based on commanded-extreme-adapter.

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Hex package

Changelog

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Getting started

The package can be installed from hex as follows.

1. Add commanded_spear_adapter to your list of dependencies in mix.exs:

   def deps do
     [{:commanded_spear_adapter, "~> 0.2"}]
   end

2. Define and configure your Commanded application:

   defmodule MyApp.Application do
     use Commanded.Application, otp_app: :my_app
   end

3. Configure the Commanded application to use the Commanded.EventStore.Adapters.Spear adapter and set the connection settings for the Event Store you are using:

   # config/config.exs
   config :my_app, MyApp.Application,
     event_store: [
       adapter: Commanded.EventStore.Adapters.Spear,
       serializer: Commanded.Serialization.JsonSerializer,
       stream_prefix: "myapp",
       spear: [
         connection_string: "esdb://localhost:2113"
       ]
     ]

   Refer to the Spear library documentation for details on the available connection settings.

   Note: Stream prefix must not contain a dash character ("-").

Partition

This adapter does not support partitioning via the partition_by option.

Multi-node setup

commanded_spear_adapter uses Erlang's :global registry to prevent duplicate subscriptions by stream/name.

Use a serializer other than JSON

To serialize and deserialize events in formats other than JSON, you must specify the content-type of the event body.

# config/config.exs
config :my_app, MyApp.Application,
  event_store: [
    adapter: Commanded.EventStore.Adapters.Spear,
    serializer: MyApp.MessagePackSerializer,
    content_type: "application/x-msgpack"
    ...
  ]

The content_type settings defaults to application/json.

Running the Event Store

You must run the Event Store with all projections enabled and standard projections started.

Use the --run-projections=all --start-standard-projections=true flags when running the Event Store executable.

Credits

• Ben Smith for commanded and commanded-extreme-adapter
• Michael Davis for spear
• Fabrizio Sestito hacking on this during SUSE/openSUSE Hack Week 21