instructure/canvas-lms · error

This assignment can't be duplicated

Error message

This assignment can't be duplicated

What it means

AbstractAssignment#duplicate refuses to duplicate assignments whose can_duplicate? is false — assignments carrying non-cloneable associations (external tool/LTI submissions, quizzes with certain settings, discussions, etc.) raise this error up front.

Solutions

1. Check assignment.can_duplicate? before calling duplicate and hide/disable the Duplicate affordance otherwise
2. Use the supported duplicate path for quizzes/LTI tools (e.g. tool-provided duplicate handling)
3. If a new assignment type should be duplicable, update can_duplicate? and the duplication logic in abstract_assignment.rb

Example fix

// before
const canDuplicate = true; // assumed
// after
const canDuplicate = assignment.canDuplicate && !(assignment.externalToolTagId);
if (canDuplicate) duplicateAssignment(assignment); else showDuplicateDisabledTooltip();

const canDuplicate = assignment.canDuplicate !== false &&
  !assignment.externalToolTagId &&
  !['quiz','discussion_topic'].includes(assignment.submissionTypes?.[0]);
if (!canDuplicate) throw new SkipError('Assignment cannot be duplicated');

function isDuplicable(a) {
  return a != null && typeof a.id === 'number' && a.canDuplicate === true;
}

try {
  await duplicateAssignment(assignmentId);
} catch (e) {
  if (e.message.includes("can't be duplicated")) {
    showError('This assignment type cannot be duplicated.');
  }
}

When it happens

Trigger: Calling assignment.duplicate (or the duplicate assignment UI/API action) on an assignment where can_duplicate? returns false: LTI/external-tool assignments, assignments with submissions or provisional grades, unsupported discussion topics.

Common situations: Users clicking Duplicate on an external tool assignment; scripts bulk-duplicating mixed assignment sets; new submission types added without updating can_duplicate?.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

• Must be a group assignment to create group overrides
• Peer review sub assignment exists
• A course did not pass validation
• A # user did not pass validation (user: # , # : # , error…
• A maximum of 50 assessees can be provided at once

AI-assisted analysis of instructure/canvas-lms@1c9f0bb801 (2026-09-15). Data as JSON: /api/errors/998bfbdf613280d0. Report an issue: GitHub.

Appendix: source

Thrown at app/models/abstract_assignment.rb:385

  end

  # The relevant associations that are copied are:
  #
  # learning_outcome_alignments, rubric_association, wiki_page,
  # assignment_configuration_tool_lookups
  #
  # In the case of wiki_page, a new wiki_page will be created.  The underlying
  # rubric association, however, will simply point to the original rubric
  # rather than copying the rubric.
  #
  # Other has_ relations are not duplicated for various reasons.
  # These are:
  #
  # attachments, submissions, provisional_grades, lti stuff, discussion_topic
  # ignores, moderated_grading_selections, teacher_enrollment
  # TODO: Try to get more of that stuff duplicated
  def duplicate(opts = {})
    raise "This assignment can't be duplicated" unless can_duplicate?

    # Don't clone a new record
    return self if new_record?

    default_opts = {
      discussion_topic_for_checkpoints: nil,
      duplicate_wiki_page: true,
      duplicate_discussion_topic: true,
      duplicate_plagiarism_tool_association: true,
      duplicate_asset_processors: true,
      copy_title: nil,
      user: nil
    }
    opts_with_default = default_opts.merge(opts)

    result = clone
    result.saving_user = opts[:user]
    result.all_submissions.clear

View on GitHub (pinned to 1c9f0bb801)