instructure/canvas-lms · error · PeerReview::InvalidAssignmentSubmissionTypesError

Peer reviews cannot be used with Discussion Topic…

Error message

Peer reviews cannot be used with Discussion Topic assignments

What it means

The same validate_assignment_submission_types method raises PeerReview::InvalidAssignmentSubmissionTypesError when `assignment.submission_types == "discussion_topic"`. Discussion topic assignments are excluded from peer review sub assignments, so the library rejects them.

Solutions

1. Use a standard online-submission assignment instead of a graded discussion for peer reviews.
2. Check `assignment.submission_types == "discussion_topic"` and skip peer review creation for those.
3. Note that legacy discussion_topic peer review behavior differs from the new sub assignment flow; keep using the legacy path for discussions.

Example fix

// before
PeerReview::SubAssignmentCreator.new(assignment: discussion_assignment).call
// after
unless discussion_assignment.submission_types == "discussion_topic"
  PeerReview::SubAssignmentCreator.new(assignment: discussion_assignment).call
end

raise ArgumentError, "discussion topics cannot use peer review sub assignments" if assignment.submission_types == "discussion_topic"

begin
  service.call
rescue PeerReview::InvalidAssignmentSubmissionTypesError => e
  render json: { error: e.message }, status: :unprocessable_entity
end

When it happens

Trigger: Enabling peer reviews / creating a peer review sub assignment on an assignment whose submission_types is exactly 'discussion_topic'.

Common situations: Graded discussions with peer reviews requested by instructors; automation enabling peer review for every assignment type in a course; API clients copying settings from discussion assignments.

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

• Due date cannot be before available from date
• Invalid parent assignment
• Must be a group assignment to create group overrides
• Peer review sub assignment does not exist
• Peer review sub assignment exists

AI-assisted analysis of instructure/canvas-lms@1c9f0bb801 (2026-09-15). Data as JSON: /api/errors/7062f89f0822864a. Report an issue: GitHub.

Appendix: source

Thrown at app/services/peer_review/validations.rb:49

  end

  def validate_feature_enabled(assignment)
    unless assignment.context.feature_enabled?(:peer_review_allocation_and_grading)
      raise PeerReview::FeatureDisabledError, I18n.t("Peer Review Allocation and Grading feature flag is disabled")
    end
  end

  def validate_grading_type(grading_type)
    raise PeerReview::InvalidGradingTypeError, I18n.t("Peer review sub assignments cannot have a not_graded grading type") if grading_type == "not_graded"
  end

  def validate_assignment_submission_types(assignment)
    if assignment.external_tool?
      raise PeerReview::InvalidAssignmentSubmissionTypesError, I18n.t("Peer reviews cannot be used with External Tool assignments")
    end

    if assignment.submission_types == "discussion_topic"
      raise PeerReview::InvalidAssignmentSubmissionTypesError, I18n.t("Peer reviews cannot be used with Discussion Topic assignments")
    end
  end

  def validate_peer_review_sub_assignment_exists(assignment)
    if assignment.peer_review_sub_assignment.blank?
      raise PeerReview::SubAssignmentNotExistError, I18n.t("Peer review sub assignment does not exist")
    end
  end

  def validate_peer_review_sub_assignment_not_exist(assignment)
    if assignment.peer_review_sub_assignment.present?
      raise PeerReview::SubAssignmentExistsError, I18n.t("Peer review sub assignment exists")
    end
  end

  # Validates that peer review dates follow the restriction below
  # peer review unlock_at < peer review due_at <= peer review lock_at
  def validate_peer_review_dates(peer_review_dates)

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