Rank 1
I have this use case:
On the server I have a JSON file that changes (for example) every 15 minutes.
The client typically leaves his browser open and wants to see the changes as fast as possible.
On the server I solved it this way:
When getting the json file, the server uses a http 304 to indicate that the file hasn't changed since the last request.
Client side I solved it this way:
I have a kendo datasource, and an interval that is doing datasource.read (polling mechanism):
Problem:
The data isn't changed, but still the "change" event of the datasource is triggered.
Is there any way of achieving this with kendo datasource, without reprogramming the entire datasource with $.ajax?
Or is this maybe a good feature request :-) ?
As an extra: I don't want to use polling, but look at the Expires http header, to know when to do the next request.
My code:
01.var datasource = new k.data.DataSource({02. transport: {03. read: {05. url: 'test.txt',06. dataType: 'json'07. }08. },09. schema: {10. data: function (data) {11. return data.Layers || [];12. }13. }14.});15. 16.//polling..17.var _interval = window.setInterval(function () {18. datasource.read();19.}, 5000);20. 21.datasource.bind('change', function (e) {22. //This shouldn't be triggered every 5 seconds23. console.log(this.data().length);24.});HTTP/1.1 304 Not ModifiedLast-Modified: Mon, 02 Sep 2013 08:02:11 GMTExpires: Mon, 02 Sep 2013 08:15:00 GMTAccept-Ranges: bytesETag: "383bbbab2a7ce1:0"Server: Microsoft-IIS/7.5X-Powered-By: ASP.NETDate: Mon, 02 Sep 2013 09:23:10 GMT5 Answers, 1 is accepted
The change event of the Kendo UI data source is raised by design every time data is received. This is required in order for Kendo UI widgets to be rebound when data is refreshed. Currently the data source doesn't keep the old data and check against the new response to see if anything has changed.
If you want to use the expires HTTP header you would need to create a custom transport for the data source. In that transport you can avoid calling options.success(response) if you wish to suppress the change event. Something like this:
transport: {
read: function(options) {
$.ajax({
url: "test.txt",
success: function(response, status, xhr) {
if (xhr.status !== 304) {
options.success(response);
}
}
});
}
}
Atanas Korchev
Telerik
Rank 1
This sounds like a nice idea. Do you mind opening a feature request in our feedback portal?
Regards,
Atanas Korchev
Telerik
Rank 1
Rank 1
Also thanks for the feature request. I was going to do this, but you have beaten me in time. I gave it 3 votes.
I'm going to add another feature request, to automatically re-read the datasource on the moment the Expires-http-header indicates.
This is a standard http header that is used very often in cooperation with http 304.
kind regards