The problem might be query.ref('+page.sales')
, you probably want something like query.ref('_page.sales')
instead.
Try the following, and make sure that you have added data to the collection.
var query = model.query('sales.dept',{price:100});
query.subscribe(function(err) {
query.ref('_page.sales');
console.log('Data', query.get());
});