1 files changed, 67 insertions, 0 deletions
diff --git a/app/graphql/resolvers/concerns/resolves_merge_requests.rb b/app/graphql/resolvers/concerns/resolves_merge_requests.rb
new file mode 100644
index 00000000000..a2140728a27
--- /dev/null
+++ b/app/graphql/resolvers/concerns/resolves_merge_requests.rb
@@ -0,0 +1,67 @@
+# frozen_string_literal: true
+
+# Mixin for resolving merge requests. All arguments must be in forms
+# that `MergeRequestsFinder` can handle, so you may need to use aliasing.
+module ResolvesMergeRequests
+  extend ActiveSupport::Concern
+  include LooksAhead
+
+  included do
+    type Types::MergeRequestType, null: true
+  end
+
+  def resolve_with_lookahead(**args)
+    args[:iids] = Array.wrap(args[:iids]) if args[:iids]
+    args.compact!
+
+    if project && args.keys == [:iids]
+      batch_load_merge_requests(args[:iids])
+    else
+      args[:project_id] ||= project
+
+      apply_lookahead(MergeRequestsFinder.new(current_user, args).execute)
+    end.then(&(single? ? :first : :itself))
+  end
+
+  def ready?(**args)
+    return early_return if no_results_possible?(args)
+
+    super
+  end
+
+  def early_return
+    [false, single? ? nil : MergeRequest.none]
+  end
+
+  private
+
+  def batch_load_merge_requests(iids)
+    iids.map { |iid| batch_load(iid) }.select(&:itself) # .compact doesn't work on BatchLoader
+  end
+
+  # rubocop: disable CodeReuse/ActiveRecord
+  def batch_load(iid)
+    BatchLoader::GraphQL.for(iid.to_s).batch(key: project) do |iids, loader, args|
+      query = args[:key].merge_requests.where(iid: iids)
+
+      apply_lookahead(query).each do |mr|
+        loader.call(mr.iid.to_s, mr)
+      end
+    end
+  end
+  # rubocop: enable CodeReuse/ActiveRecord
+
+  def unconditional_includes
+    [:target_project]
+  end
+
+  def preloads
+    {
+      assignees: [:assignees],
+      labels: [:labels],
+      author: [:author],
+      milestone: [:milestone],
+      head_pipeline: [:merge_request_diff, { head_pipeline: [:merge_request] }]
+    }
+  end
+end