Grid SelectionMode.MULTI is missing the header checkbox to select all for BackEndDataProvider - vaadin-grid

Question

I am working with a new application written to version 8 (currently testing with 8.1.0.rc2).
The issue surrounds the "select all" checkbox that appears in the header of a Grid when using SelectionMode.MULTI. In particular, the problem is that the checkbox appears and operates as expected when the DataProvider implements InMemoryDataProvider, but the checkbox does not appear when the DataProvider implements BackEndDataProvider.
The following code creates two grids that differ only in whether they use InMemory or BackEnd:
public class Test {
public void setName(String name) {
this.name = name;
}
public String getName() {
return name;
}
private String name;
}
public class TestView extends BaseView {
public TestView() {
super("Test");
addComponent(new TestGrid(new TestDataProvider0()));
addComponent(new TestGrid(new TestDataProvider1()));
}
}
public class TestGrid extends Grid<Test> {
public TestGrid(DataProvider<Test, ?> dataProvider) {
setHeightByRows(4);
setSelectionMode(SelectionMode.MULTI);
setDataProvider(dataProvider);
addColumn(Test::getName).setCaption("Name");
}
}
public class TestDataProvider0 extends AbstractDataProvider<Test, SerializablePredicate<Test>> implements
BackEndDataProvider<Test, SerializablePredicate<Test>> {
public Stream<Test> fetch(Query<Test, SerializablePredicate<Test>> query) {
List<Test> tests = new ArrayList<>(query.getLimit());
for (int i = 0; i < query.getLimit(); i++) {
Test test = new Test();
test.setName(String.valueOf(query.getOffset() + i));
tests.add(test);
}
return tests.stream();
}
public int size(Query<Test, SerializablePredicate<Test>> query) {
return 100;
}
public void setSortOrders(List<QuerySortOrder> sortOrders) {
}
}
public class TestDataProvider1 extends AbstractDataProvider<Test, SerializablePredicate<Test>> implements
InMemoryDataProvider<Test> {
public Stream<Test> fetch(Query<Test, SerializablePredicate<Test>> query) {
List<Test> tests = new ArrayList<>(query.getLimit());
for (int i = 0; i < query.getLimit(); i++) {
Test test = new Test();
test.setName(String.valueOf(query.getOffset() + i));
tests.add(test);
}
return tests.stream();
}
public int size(Query<Test, SerializablePredicate<Test>> query) {
return 100;
}
public SerializablePredicate<Test> getFilter() {
return null;
}
public void setFilter(SerializablePredicate<Test> filter) {
}
public SerializableComparator<Test> getSortComparator() {
return null;
}
public void setSortComparator(SerializableComparator<Test> comparator) {
}
}
Here is how the grids are rendered:
Have I missed a critical step in setting up my BackEnd-based data provider/grid? The related documentation does not seem to address this issue.
Is there a known issue related to this?
Is select-all not available by design? Obviously, this could interact really badly with the concept of lazy-loading on a large data set...

Answer 1

MultiSelectionModelImpl has this method:
protected void updateCanSelectAll() {
switch (selectAllCheckBoxVisibility) {
case VISIBLE:
getState(false).selectAllCheckBoxVisible = true;
break;
case HIDDEN:
getState(false).selectAllCheckBoxVisible = false;
break;
case DEFAULT:
getState(false).selectAllCheckBoxVisible = getGrid()
.getDataProvider().isInMemory();
break;
default:
break;
}
}
This indicates that the default behavior for non-in-memory providers is to not show the select-all checkbox, but that this behavior can be overridden by setting the visibility to VISIBLE.
Tweaking the original code here:
public class TestGrid extends Grid<Test> {
public TestGrid(DataProvider<Test, ?> dataProvider) {
setHeightByRows(4);
MultiSelectionModel<Test> selectionModel = (MultiSelectionModel<Test>) setSelectionMode(SelectionMode.MULTI);
selectionModel.setSelectAllCheckBoxVisibility(SelectAllCheckBoxVisibility.VISIBLE);
setDataProvider(dataProvider);
addColumn(Test::getName).setCaption("Name");
}
}
Specifically, this call is required for the checkbox to appear for data providers that implement BackEndDataProvider:
MultiSelectionModel<Test> selectionModel = (MultiSelectionModel<Test>) setSelectionMode(SelectionMode.MULTI);
selectionModel.setSelectAllCheckBoxVisibility(SelectAllCheckBoxVisibility.VISIBLE);
With this change, the select-all checkbox now appears: