feature: batch mapper

ruby_event_store/lib/ruby_event_store.rb

@@ -28,6 +28,7 @@
 require_relative "ruby_event_store/mappers/transformation/stringify_metadata_keys"
 require_relative "ruby_event_store/mappers/transformation/symbolize_metadata_keys"
 require_relative "ruby_event_store/mappers/transformation/preserve_types"
+require_relative "ruby_event_store/mappers/batch_mapping"
 require_relative "ruby_event_store/mappers/pipeline"
 require_relative "ruby_event_store/mappers/pipeline_mapper"
 require_relative "ruby_event_store/mappers/default"
@@ -46,4 +47,4 @@
 require_relative "ruby_event_store/instrumented_repository"
 require_relative "ruby_event_store/instrumented_dispatcher"
 require_relative "ruby_event_store/instrumented_subscriptions"
-require_relative "ruby_event_store/event_type_resolver"
+require_relative "ruby_event_store/event_type_resolver"

ruby_event_store/lib/ruby_event_store/mappers/batch_mapping.rb

@@ -0,0 +1,11 @@
+# frozen_string_literal: true
+
+module RubyEventStore
+  module Mappers
+    module BatchMapping
+      def map_records_to_events(records)
+        records.map { |record| record_to_event(record) }
+      end
+    end
+  end
+end

ruby_event_store/lib/ruby_event_store/mappers/instrumented_mapper.rb

@@ -3,6 +3,8 @@
 module RubyEventStore
   module Mappers
     class InstrumentedMapper
+      include BatchMapping
+
       def initialize(mapper, instrumentation)
         @mapper = mapper
         @instrumentation = instrumentation

ruby_event_store/lib/ruby_event_store/mappers/pipeline_mapper.rb

@@ -3,6 +3,8 @@
 module RubyEventStore
   module Mappers
     class PipelineMapper
+      include BatchMapping
+
       def initialize(pipeline)
         @pipeline = pipeline
       end

ruby_event_store/lib/ruby_event_store/specification_reader.rb

@@ -8,6 +8,10 @@ class SpecificationReader
     def initialize(repository, mapper)
       @repository = repository
       @mapper = mapper
+      @batch_mapper = mapper.respond_to?(:map_records_to_events)
+      if !@batch_mapper
+        warn "Your custom mapper does not support batch reading. This behaviour will be deprecated in future releases. You can include RubyEventStore::Mappers::BatchMapping to your mapper to make it compatible."
+      end
     end
 
     # @api private
@@ -20,7 +24,15 @@ def one(specification_result)
     # @api private
     # @private
     def each(specification_result)
-      repository.read(specification_result).each { |batch| yield batch.map { |record| mapper.record_to_event(record) } }
+      if @batch_mapper
+        repository.read(specification_result).each { |batch|
+          yield mapper.map_records_to_events(batch)
+        }
+      else
+        repository.read(specification_result).each { |batch|
+          yield batch.map { |record| mapper.record_to_event(record) }
+        }
+      end
     end
 
     # @api private

ruby_event_store/spec/specification_reader_spec.rb

@@ -0,0 +1,52 @@
+
+# frozen_string_literal: true
+
+require "spec_helper"
+require "ruby_event_store/spec/event_repository_lint"
+
+module RubyEventStore
+  ::RSpec.describe SpecificationReader do
+    mk_repository = -> { InMemoryRepository.new }
+
+    let(:repository) {
+      mk_repository.call.tap do |repo|
+        repo.append_to_stream(
+          [SRecord.new(event_id: "fbce0b3d-40e3-4d1d-90a1-901f1ded5a4a")],
+          Stream.new("other"),
+          ExpectedVersion.none
+        )
+      end
+    }
+    let(:mapper_klass) {
+      Class.new(Mappers::Default) do
+        attr_reader :invoked_map_records_to_events
+
+        def map_records_to_events(...)
+          @invoked_map_records_to_events = true
+          super(...)
+        end
+      end
+    }
+
+    specify "reading invokes the mapper in batches" do
+      mapper = mapper_klass.new
+      specification = Specification.new(
+        SpecificationReader.new(repository, mapper)
+      )
+      specification.to_a
+      expect(mapper.invoked_map_records_to_events).to eq(true)
+    end
+
+    specify "specification can still handle non batch compatible mappers" do
+      mapper_klass.undef_method(:map_records_to_events)
+      mapper = mapper_klass.new
+      expect(Warning).to receive(:warn).with("Your custom mapper does not support batch reading. This behaviour will be deprecated in future releases. You can include RubyEventStore::Mappers::BatchMapping to your mapper to make it compatible.\n", { category: nil }).once
+
+      specification = Specification.new(
+        SpecificationReader.new(repository, mapper)
+      )
+      specification.to_a
+      expect(mapper.invoked_map_records_to_events).to_not eq(true)
+    end
+  end
+end