Querying on the client

Question

I need to do some querying client side. As a simplified example, this works great:
var filter = "(substringof('Futterkiste', CustomerName) eq true)";
msls.application.activeDataWorkspace.ApplicationData.Customers
.filter(filter)
.top(1)
.execute()
.then(function (results) {
if (results.results.length >= 0) {
screen.prpCustomer = results.results[0];
function (error) {
alert(error);
However, if I already have the customer data loaded (or at least available as a local screen query), how can I filter and use that collection?  This produces Error: Object doesn't support property or method 'filter'.
var filter = "(substringof('Futterkiste', CustomerName) eq true)";
screen.getCustomers()
.filter(filter) // filter not supported
.top(1)
.execute() // is this necessary with getCustomers?
.then(function (results) {
if (results.results.length >= 0) {
screen.prpCustomer = results.results[0];
function (error) {
alert(error);
I also tried screen.Customers instead of screen.getCustomers and got the same error result.  How do you filter screen collections?  Or, should I just use the datasource and be happy something works?

Answer 1

Hi Hessc,
You can override the screen collection query with a hack like this:
In the screen design: Edit Query and add optional parameter called filterString - no filter needed.  Then do this in screen_created.   Upon setting screen.filterString, your collection will filter.
myapp.BrowseCustomers.created = function (screen) {
// Write code here.
screen.details.properties["Customers"]._entry.simpleDescriptor.createQuery =
function (filterString) {
return this.dataWorkspace.ApplicationData["Customers"]
.filter(filterString);
}; screen.filterString = "substringof('Futterkiste', CustomerName)";
The code above has limitations like, if your screen is based on a query having filters, it will override those and base on the table.  A more flexible way is to use a Monkey Patch to append the this filter on top of the screen query like so:
http://joshuabooker.com/Blog/Post/8/Monkey-Patched-LightSwitch-Screen-Collection-Queries
HTH,
Josh