1 files changed, 52 insertions, 0 deletions
diff --git a/app/graphql/mutations/concerns/mutations/assignable.rb b/app/graphql/mutations/concerns/mutations/assignable.rb
new file mode 100644
index 00000000000..f6f4b744f4e
--- /dev/null
+++ b/app/graphql/mutations/concerns/mutations/assignable.rb
@@ -0,0 +1,52 @@
+# frozen_string_literal: true
+
+module Mutations
+  module Assignable
+    extend ActiveSupport::Concern
+
+    included do
+      argument :assignee_usernames,
+               [GraphQL::STRING_TYPE],
+               required: true,
+               description: 'The usernames to assign to the resource. Replaces existing assignees by default.'
+
+      argument :operation_mode,
+               Types::MutationOperationModeEnum,
+               required: false,
+               description: 'The operation to perform. Defaults to REPLACE.'
+    end
+
+    def resolve(project_path:, iid:, assignee_usernames:, operation_mode: Types::MutationOperationModeEnum.enum[:replace])
+      resource = authorized_find!(project_path: project_path, iid: iid)
+
+      Gitlab::QueryLimiting.whitelist('https://gitlab.com/gitlab-org/gitlab/issues/36098') if resource.is_a?(MergeRequest)
+
+      update_service_class.new(
+        resource.project,
+        current_user,
+        assignee_ids: assignee_ids(resource, assignee_usernames, operation_mode)
+      ).execute(resource)
+
+      {
+        resource.class.name.underscore.to_sym => resource,
+        errors: errors_on_object(resource)
+      }
+    end
+
+    private
+
+    def assignee_ids(resource, usernames, operation_mode)
+      assignee_ids = []
+      assignee_ids += resource.assignees.map(&:id) if Types::MutationOperationModeEnum.enum.values_at(:remove, :append).include?(operation_mode)
+      user_ids = UsersFinder.new(current_user, username: usernames).execute.map(&:id)
+
+      if operation_mode == Types::MutationOperationModeEnum.enum[:remove]
+        assignee_ids -= user_ids
+      else
+        assignee_ids |= user_ids
+      end
+
+      assignee_ids
+    end
+  end
+end