Allow iteration ids to be passes as a Global ID

but still support passing raw ids

changelogs/unreleased/bw-iteration-globalid.yml

+---
+title: Allow a Global ID to be used when filtering issue by iterationId in GraphQL
+merge_request: 57620
+author:
+type: changed

ee/app/graphql/ee/resolvers/issues_resolver.rb

@@ -9,7 +9,7 @@ module EE
       prepended do
         argument :iteration_id, [::GraphQL::ID_TYPE, null: true],
                  required: false,
-                 description: 'Iterations applied to the issue.'
+                 description: 'List of iteration Global IDs applied to the issue.'
         argument :epic_id, GraphQL::STRING_TYPE,
                  required: false,
                  description: 'ID of an epic associated with the issues, "none" and "any" values are supported.'
@@ -18,8 +18,25 @@ module EE
                  description: 'Weight applied to the issue, "none" and "any" values are supported.'
       end
 
+      override :resolve_with_lookahead
+      def resolve_with_lookahead(**args)
+        args[:iteration_id] = iteration_ids_from_args(args) if args[:iteration_id].present?
+
+        super
+      end
+
       private
 
+      # Originally accepted a raw model id. Now accept a gid, but allow a raw id
+      # for backward compatibility
+      def iteration_ids_from_args(args)
+        args[:iteration_id].map do |id|
+          ::GitlabSchema.parse_gid(id, expected_type: ::Iteration).model_id
+        rescue ::Gitlab::Graphql::Errors::ArgumentError
+          id
+        end
+      end
+
       override :preloads
       def preloads
         super.merge(

ee/spec/graphql/ee/resolvers/issues_resolver_spec.rb

@@ -67,8 +67,23 @@ RSpec.describe Resolvers::IssuesResolver do
       end
 
       describe 'filtering by iteration' do
-        it 'returns issues with iteration' do
-          expect(resolve_issues(iteration_id: [iteration1.id.to_s])).to contain_exactly(issue1)
+        let_it_be(:iteration1) { create(:iteration, group: group) }
+        let_it_be(:iteration2) { create(:iteration, group: group) }
+        let_it_be(:issue_with_iteration1) { create(:issue, project: project, iteration: iteration1) }
+        let_it_be(:issue_with_iteration2) { create(:issue, project: project, iteration: iteration2) }
+        let_it_be(:issue_without_iteration) { create(:issue, project: project) }
+
+        it 'returns issues with iteration using raw id' do
+          expect(resolve_issues(iteration_id: [iteration1.id])).to contain_exactly(issue_with_iteration1)
+        end
+
+        it 'returns issues with iteration using global id' do
+          expect(resolve_issues(iteration_id: [iteration1.to_global_id])).to contain_exactly(issue_with_iteration1)
+        end
+
+        it 'returns issues with list iterations using global id' do
+          expect(resolve_issues(iteration_id: [iteration1.to_global_id, iteration2.to_global_id]))
+            .to contain_exactly(issue_with_iteration1, issue_with_iteration2)
         end
       end