I have a grouping store and need to assign the url at runtime after the user has chosen some criteria.

    var storeAVL = new Ext.data.GroupingStore(
        proxy: new Ext.data.HttpProxy(),
        reader:     new Ext.data.JsonReader({root: 'Rows'}, [
                    {name: 'M_AverageSpeed', type: 'int'},
                    {name: 'M_City'},
                    {name: 'M_Country'},
                    {name: 'M_Date', type: 'date', dateFormat: 'j/n/Y'},
                    {name: 'M_Distance', type: 'int'},
                    {name: 'M_Duration', type: 'int'},
                    {name: 'M_Location'},            
                    {name: 'M_Time', type: 'date', dateFormat: 'h:i:s'},
                    {name: 'M_TopSpeed', type: 'int'}
        id:             'tabs-body-report-store',
        sortInfo:       {field: 'M_Time', direction: "ASC"},
        groupField:     'M_Date',
        autoLoad: false
    storeAVL.proxy = new Ext.data.HttpProxy({
                        url: '/api/BusinessLogic/....', 
                        timeout: 300000,
                        method: "GET",
                        disableCaching: false,
                        timeout:        60000

      callback: function(){
I am assigning the store to the datagrid initially and then need to assign the URL after.

thanks in advance for any help.