Server Grouping with virtualization is duplicating records

[markcz]

Hi, we were testing Telerik Server Grouping with virtualization, as it is shown in the example for it and we are seeing strange behaviour.

When I select a group which has enough records inside, the scrolling in the group down to make it request another page will actually append again the same records which are already displayed - from the first page actually.

The easiest steps to reproduce this behaviour is

1. Go to demo page 

https://demos.telerik.com/kendo-ui/grid/server-grouppaging-virtualization and click to Edit in Dojo. It opens https://dojo.telerik.com/afoCefOJ

Then, to get rid of narrow groups I will change grouping from 

group: [{
                        field: "city",
                        dir: "asc"
                    }, {
                        field: "companyName",
                        dir: "asc"
                    }],

to

group: [{
                        field: "city",
                        dir: "asc"
                    }],

and also adjust pageSize to 10:

pageSize: 10,

2. Now, when I Run example, open Chrome Debug tools to Network traffic and expand Shady shores, I get records starting with:

GC30TRSSMTI706Z, Ireland

I can see first request starting wtih Page:1

3. Now I scroll the virtual view just a bit down to get another 10 records. Surprisingly, I get same records again.

GC30TRSSMTI706Z, Ireland

Is it expected behaviour, or how can I fix it to scroll to next records on another request ?

Thank you kindly,

Martin

[Neli]

Hi Martin,

Note, that when virtual scrolling is enabled the page size and the Grid height should be taken into account. As described in the Known Limitation section of the Virtual Scrolling article linked below - the page size of the Grid must be over three times larger than the number of visible table rows in the data area.

- https://docs.telerik.com/kendo-ui/controls/data-management/grid/scrolling/virtual-scrolling#known-limitations

I hope this helps.

Regards,

Neli
Progress Telerik

[markcz]

Hello Neli,
thank you for your reply.
I went through the limitations link you shared and as well tried your suggestion with increasing the page size to 200 items. My grid is about 400px high, so the number of visible rows I got was about 7.

Unfortunately It was still sending request for first page for the second time, when I scrolled down over 200th record.

We have prepared a dojo link here:
https://dojo.telerik.com/afoCefOJ/3.
Then I manually clicked to order by CustomerID and expanded Brazil.

In the dataset, Brazil returned first page, with total number of items 983.
The first item in the page was with Customer ID 00PFNDV1KNUOACC, Shop named "Spécialités du monde"
so I tried scrolling down in the group and my browser has sent again another request for page: 1.


This is how the first and second request body looks:
```
sort: customerID-asc
page: 1
pageSize: 200
group:
filter: country~eq~'Brazil'
```

This looks like a bug to me. Or is there anything else we can try ?
thank you very much,
Martin

[Neli]

Hello Martin,

I will need a little bit more time to review the issue and the provided details. I will get back to you once I have some information to share.

Thank you very much for your patience.

Regards,
Neli
Progress Telerik

[Neli]

Hi Martin,

 I would like to apologize for the big delay in my reply. Thank you very much for your patience, I appreciate it. 

I discussed the issue and the provided example with a developer from the team. However, the described behavior could be observed in some scenarios. As the issue is discussed in our Forum I would suggest you go through the Forum thread linked below, as it explains the described behavior in more detail. 

- https://www.telerik.com/forums/grid-with-remote-virtual-scrolling-fires-mutiple-read-requests-when-scrolling-fast

Thank you once again for your patience.

Regards,
Neli
Progress Telerik