DynamoDB expression to Update if item does not exist or other field equals certain value

Question

I get the following error when I try to do a conditional update:

Invalid ConditionExpression: Syntax error; token: "-", near: "PageRouteee1181aa-8035"

I have the following class:

public class RestaurantPageRouteItem
{
    [DynamoDBHashKey]
    public string PageRoute { get; set; }

    public string RestaurantId { get; set; }
}

And Im creating the following expression:

new Expression
{
    ExpressionStatement = $"attribute_not_exists({item.PageRoute}) OR {item.RestaurantId} = :restaurantid",
    ExpressionAttributeValues =
    {
        [":restaurantid"] = item.RestaurantId
    }
}

Answer 1

Managed to come up with the following:

new Expression {
 ExpressionStatement =
  "(attribute_not_exists(#ID) OR :id = #ID) OR " +
  "(attribute_not_exists(PageRoute))",
  ExpressionAttributeValues = {
   [":id"] = item.RestaurantId
  },
  ExpressionAttributeNames = {
   ["#ID"] = "RestaurantId"
  }
}