Grid selected items returns wrong data

[knoobie]

Description

When selecting "old" data - the grid does not update the selected items correctly.

Expected outcome

• Clicking Print current selection returns updated data

Minimal reproducible example

import com.vaadin.flow.component.button.Button;
import com.vaadin.flow.component.grid.Grid;
import com.vaadin.flow.component.grid.Grid.SelectionMode;
import com.vaadin.flow.component.grid.GridMultiSelectionModel;
import com.vaadin.flow.component.html.Paragraph;
import com.vaadin.flow.component.orderedlayout.VerticalLayout;
import com.vaadin.flow.data.provider.ListDataProvider;
import com.vaadin.flow.router.Route;
import java.util.ArrayList;
import java.util.Collection;
import java.util.List;
import java.util.Objects;

@Route(value = "grid-bug")
public class GridBugView extends VerticalLayout {

  public GridBugView() {
    var grid = new Grid<MyBean>();
    grid.setSelectionMode(SelectionMode.MULTI);
    grid.addColumn(e -> e.id).setHeader("ID");
    grid.addColumn(e -> e.increasingValue).setHeader("Value");

    grid.setItems(new MyBeanDataProvider(callExternalServiceToGetLatestData(0, 0, 0)));

    add(grid);
    add(new Button("Increment selected items", e -> {
      var selectedItems = grid.getSelectedItems();

      grid.setItems(new MyBeanDataProvider(callExternalServiceToGetLatestData(
        selectedItems.contains(new MyBean("1", 0)) ? 1 : 0,
        selectedItems.contains(new MyBean("2", 0)) ? 1 : 0,
        selectedItems.contains(new MyBean("3", 0)) ? 1 : 0
      )));

      if (grid.getSelectionModel() instanceof GridMultiSelectionModel<MyBean> selectionModel) {
        // reselect after applying new data provider
        // this creates the problem - this does not "selects" the items from within the grid, but the old instances with value=0 which are passed as arguments.
        // -- Expectations: the grid is selecting the items that are stored inside the grid.
        selectionModel.selectItems(selectedItems.toArray(MyBean[]::new));
      }
    }));

    add(new Button("Print current selection", e -> {
      add(new Paragraph("Selected items: " + grid.getSelectedItems().size()));
      grid.getSelectedItems().forEach(item -> {
        add(new Paragraph("item: " + item.id + " - " + item.increasingValue));
      });
    }));
  }

  static List<MyBean> callExternalServiceToGetLatestData(int _1, int _2, int _3) {
    var data = new ArrayList<MyBean>();
    data.add(new MyBean("1", _1));
    data.add(new MyBean("2", _2));
    data.add(new MyBean("3", _3));
    return data;
  }


  static class MyBeanDataProvider extends ListDataProvider<MyBean> {

    MyBeanDataProvider(Collection<MyBean> items) {
      super(items);
    }

    @Override
    public Object getId(MyBean item) {
      return item.id;
    }
  }

  static class MyBean {

    final String id;
    final int increasingValue;

    MyBean(String id, int increasingValue) {
      this.id = id;
      this.increasingValue = increasingValue;
    }

    @Override
    public boolean equals(Object o) {
      if (o == null || getClass() != o.getClass()) {return false;}
      return Objects.equals(id, ((MyBean) o).id);
    }

    @Override
    public int hashCode() {
      return Objects.hashCode(id);
    }
  }
}

Steps to reproduce

1. Select 2 and 3
2. Press Increment selected items
3. Press Print current selection
4. Expectation: grid::getSelectedItems() contains the correct values (2=1, 3=1)

Environment

Vaadin version(s): 25.2.1 / latest

Browsers

No response

[sissbruecker]

I think we do not guarantee that the items in selected items match "live data", we only guarantee that their identity matches. Though we should definitely state this somewhere in the documentation.

This design has been identified as flawed already and some ideas were put forth, but there are no substantial plans yet. Updating the selected items on data provider updates could be also considered, but that would require figuring some things:

• This can be easily implemented for in-memory data providers, but for lazy providers it would arguably require a new API to query for the "fresh" version of a set of items. That also complicates the behavior somewhat in that in some configurations you get live data and in others you don't.
• In your example you pass the old items to selectItems and then expect them to be "upgraded" to their live versions from the data provider. I feel that would be unexpected and could trip people up (for example comparing selected items by reference). Maybe the grid should not tamper with data passed to it, but should only do the upgrade on data provider changes, when configured to preserve existing selection.

For now a workaround is to map the grid selection to live data with a separate query, potentially with a caching layer to avoid duplicate queries when selection didn't change.