Selection behaviour breaks for non-determinate sort orders

[cmrgKoradir]

Reproduce

• set up a callbacks-based selection grid with items that share some properties (e.g. have the same creation date)
• generate more than one page worth of items
• add sorting support in the backend
• intentionally do not ensure a determinate sort order (e.g. do not specify an order for items with the same creation date)
• in the selection grid sort by that property (i.e. creation date, in our example)
• click on some rows in the selection grid

IS

• seemingly random rows get selected

SHOULD

• the rows clicked should get selected

[cmrgKoradir]

To be clear, I'd still consider it best practice to enforce a determinate sort order.

But I do not think the selection grid should break in the way it does if you do not.

[javier-godoy]

Hello. Shift-selection (which involves fetching all the rows in-between) requires that rows are always fetched in the same order, otherwise it will fail to find and select contiguous rows. Single-click happens to be implemented to select a range of length one, and as a result, it faces the same restriction.

selection-grid-flow/selection-grid-flow/src/main/resources/META-INF/resources/frontend/src/selection-grid.js

Line 62 in 770bab5

this.$server.selectRangeOnly(index, index);

selection-grid-flow/selection-grid-flow/src/main/java/com/vaadin/componentfactory/selectiongrid/SelectionGrid.java

Line 200 in d89d87f

private Optional<Stream<T>> fetchFromProvider(int offset, int limit) {

I think it could be possible to reduce the occurrence of failures, but in general, the behavior may not be well-defined.