How to correctly append value to REST proxy URL

This is my first time using REST and I'm having a bit of trouble. I'm using EXTJS 5.1 and Parse.com. I have a table of listObjects and I only want to load the store with certain listObjects. Here is the parse REST API on what I'm trying to do http://ift.tt/1wdUu0b

Here is my store:

Code:

Ext.define('top10.store.ListObjectStore' , {
    extend : ' Ext .data.Store' ,
    require :[
        'top10.model.ListObject'
 ],

 model : 'top10.model.ListObject' ,
    proxy : {
        type : 'rest' ,
        url : 'http://ift.tt/1EG2yWI' ,
        useDefaultXhrHeader : false ,
        withCredentials : false ,
        headers : {
            'X-Parse-Application-Id' : "xxx" ,
            'X-Parse-REST-API-Key' : 'xxx' ,
            'Content-Type' : 'application/json'
 },
        reader :{
            type : 'json' ,
            rootProperty : 'results' ,
            transform: function ( data ) {
                return  data.results  ? data.results  : {results :data};
            }
        },
        writer : {
            type : 'json' ,
            writeRecordId : false
 }
    }

});

Here is what I'm doing to manipulate the proxy URL:

Code:

onCmboListSelect: function (cmbo, rec){

    var  listStore = Ext  .create('top10.store.ListObjectStore' );
 listStore.proxy .url  = listStore.proxy .url  + '/?where={"listId": "' +rec.get('objectId' )+'"}' ;
    listStore.load();
}

This works, but I'd like to believe there is a more correct way to do this. Any suggestions?



How to correctly append value to REST proxy URL