1 files changed, 82 insertions, 0 deletions
diff --git a/lib/gitlab/import_export/json/streaming_serializer.rb b/lib/gitlab/import_export/json/streaming_serializer.rb
new file mode 100644
index 00000000000..d053bf16166
--- /dev/null
+++ b/lib/gitlab/import_export/json/streaming_serializer.rb
@@ -0,0 +1,82 @@
+# frozen_string_literal: true
+
+module Gitlab
+  module ImportExport
+    module JSON
+      class StreamingSerializer
+        include Gitlab::ImportExport::CommandLineUtil
+
+        BATCH_SIZE = 100
+
+        class Raw < String
+          def to_json(*_args)
+            to_s
+          end
+        end
+
+        def initialize(exportable, relations_schema, json_writer)
+          @exportable = exportable
+          @relations_schema = relations_schema
+          @json_writer = json_writer
+        end
+
+        def execute
+          serialize_root
+
+          includes.each do |relation_definition|
+            serialize_relation(relation_definition)
+          end
+        end
+
+        private
+
+        attr_reader :json_writer, :relations_schema, :exportable
+
+        def serialize_root
+          attributes = exportable.as_json(
+            relations_schema.merge(include: nil, preloads: nil))
+          json_writer.set(attributes)
+        end
+
+        def serialize_relation(definition)
+          raise ArgumentError, 'definition needs to be Hash' unless definition.is_a?(Hash)
+          raise ArgumentError, 'definition needs to have exactly one Hash element' unless definition.one?
+
+          key, options = definition.first
+
+          record = exportable.public_send(key) # rubocop: disable GitlabSecurity/PublicSend
+          if record.is_a?(ActiveRecord::Relation)
+            serialize_many_relations(key, record, options)
+          else
+            serialize_single_relation(key, record, options)
+          end
+        end
+
+        def serialize_many_relations(key, records, options)
+          key_preloads = preloads&.dig(key)
+          records = records.preload(key_preloads) if key_preloads
+
+          records.find_each(batch_size: BATCH_SIZE) do |record|
+            json = Raw.new(record.to_json(options))
+
+            json_writer.append(key, json)
+          end
+        end
+
+        def serialize_single_relation(key, record, options)
+          json = Raw.new(record.to_json(options))
+
+          json_writer.write(key, json)
+        end
+
+        def includes
+          relations_schema[:include]
+        end
+
+        def preloads
+          relations_schema[:preload]
+        end
+      end
+    end
+  end
+end