SnapshotAggregateRoot

An extension of https://github.com/arkency/aggregate_root with support for concurrent writers.

Usage

Snapshots

Snapshots are created automatically as required by the #store method. Implementations of this class must implement 2 methods.

• #build_snapshot
• #apply_snapshot(snapshot)

Optionally Implementations may also override

• #snapshot_threshold - Override how often snapshots are taken
• #requires_snapshot?- Provide a custom implementation for when snapshots a required

Concurrent Writers

In order to be safe for current writes snapshot aggregate root exposes a #with_write_context(stream_name, event_store:) method. This method loads the aggregate, applies the block, then stores the events within a mutex so that only one concurrent writer can execute the block. Event handlers are triggered after the command is complete

The entire command handler for a snapshot aggregate root should be executed within this block eg.

  def apply_command(command)
    SomeAggregate.new.with_write_context(command.aggregate_id) do |aggregate|
      aggregate.do_command(command)
    end
  end