//store
var Store_toponimia = new Ext.data.JsonStore({
                url: '../php/ruas.php',
                root: 'rows',
                fields: ['id', 'toponimia','geojson'],
                remoteSort: true,
                remoteFilter: true,
            });

//Combo
var combo = new Ext.form.ComboBox({
        id: 'combobox_ruas',
        store: Store_toponimia,
        displayField: 'toponimia',
        valueField:'toponimia',
        typeAhead: true,
        queryMode: 'remote',
        forceSelection: true,
        triggerAction: 'query',
        lastQuery: '',
        emptyText: 'Pesquisa por Ruas',
        selectOnFocus: true,
        loadingText: "A procurar...",
        minChars  : 1,
        hideTrigger: true,
    });