How can i prevent duplicate entry with Deployd?

I'm using Deployd with Swift iOS. All I'm saving is two text strings. I just want to prevent duplicate entries.

This is how I'm checking if an element exists, to implement this just open the Deployd's dasboard choose your collection paste this snippet to POST section. Just dont forget to put your collection's name in the place of YOUR_COLLECTION_NAME. enjoy.!

var query=this; 
delete query.id;
    var resultAr = []; dpd.YOUR_COLLECTION_NAME.get(query ,function(result){
                        if (result) {
                            resultAr = result;
                            if (resultAr.length === 0){
                                emit ("success");
                             }
                            else {
                                error("same entry already exist", 400);
                            }
                        } });