Fix graphql boards filtering by iterationId

ee/app/graphql/ee/resolvers/board_item_filterable.rb

@@ -34,8 +34,22 @@ module EE
 
       def filter_by_iteration(filters)
         iteration_wildcard_id = filters.delete(:iteration_wildcard_id)
+        # passing string is not failing the check...should be an array
+        iterations = filters[:iteration_id]
 
-        if iteration_wildcard_id
+        if iterations.present? && iteration_wildcard_id
+          raise ::Gitlab::Graphql::Errors::ArgumentError, 'Incompatible arguments: iterationId, iterationWildCardId.'
+        end
+
+        if iterations.present?
+          filters[:iteration_id] = iterations.map do |global_id|
+            # TODO: remove this line when the compatibility layer is removed
+            # See: https://gitlab.com/gitlab-org/gitlab/-/issues/257883
+            parsed_id = ::Types::GlobalIDType[::Iteration].coerce_isolated_input(global_id)
+            parsed_id&.model_id
+          end
+
+        elsif iteration_wildcard_id
           filters[:iteration_id] = iteration_wildcard_id
         end
       end

ee/spec/graphql/ee/resolvers/board_list_issues_resolver_spec.rb

@@ -107,6 +107,12 @@ RSpec.describe Resolvers::BoardListIssuesResolver do
         expect(result).to contain_exactly(issue1, issue3)
       end
 
+      it 'accepts iteration iteration id' do
+        result = resolve_board_list_issues({ filters: { iteration_id: [iteration.to_global_id] } })
+
+        expect(result).to contain_exactly(issue2)
+      end
+
       context 'filterning by negated iteration' do
         it 'accepts iteration wildcard id' do
           result = resolve_board_list_issues({ filters: { not: { iteration_wildcard_id: 'CURRENT' } } })