function constraintActionToEnumType(constraintAction) {
  switch (constraintAction) {
    case 'cascade': return lf.ConstraintAction.CASCADE;
    case 'restrict': return lf.ConstraintAction.RESTRICT;
    default: throw new Error('Invalid constraint action: ' + constraintAction);
  }
}
@param {string} constraintAction
@return {!lf.ConstraintAction}
@suppress {missingRequire}