p:dataTable selections are lost after paginating a LazyDataModel

datatable, jsf-2, lazy-loading, pagination, primefaces

Solution

This is because when `SelectionFeature` is decoded a new list is created.

And if `table.getRowData(rowKeys[i])` (related to your `LazyDataModel` implementation) returns null your old selectıons in the previous page are gone.may try to solve it by changing your LazyDataModel implementation I didn't try these but take a look at this and this

Had the same problem and I think this solution is easier if you have a lot of different tables implementing LazyDataModel.

This is what I did: check if it is lazy first then add currently selected rows to the selectionList.

For primefaces 4.0

1)Override DataTableRenderer

In faces-config.xml

<render-kit>
   <renderer>
       <component-family>org.primefaces.component</component-family>
       <renderer-type>org.primefaces.component.DataTableRenderer</renderer-type>
       <renderer-class>com.package.LazyDataTableRenderer</renderer-class>
   </renderer>
</render-kit>

And

public class LazyDataTableRenderer extends DataTableRenderer {
static Map<DataTableFeatureKey,DataTableFeature> FEATURES;

    static {
        FEATURES = new HashMap<DataTableFeatureKey,DataTableFeature>();
        FEATURES.put(DataTableFeatureKey.DRAGGABLE_COLUMNS, new DraggableColumnsFeature());
        FEATURES.put(DataTableFeatureKey.FILTER, new FilterFeature());
        FEATURES.put(DataTableFeatureKey.PAGE, new PageFeature());
        FEATURES.put(DataTableFeatureKey.SORT, new SortFeature());
        FEATURES.put(DataTableFeatureKey.RESIZABLE_COLUMNS, new ResizableColumnsFeature());
        FEATURES.put(DataTableFeatureKey.SELECT, new LazySelectionFeature());
        FEATURES.put(DataTableFeatureKey.ROW_EDIT, new RowEditFeature());
        FEATURES.put(DataTableFeatureKey.CELL_EDIT, new CellEditFeature());
        FEATURES.put(DataTableFeatureKey.ROW_EXPAND, new RowExpandFeature());
        FEATURES.put(DataTableFeatureKey.SCROLL, new ScrollFeature());
    }

    @Override
    public void decode(FacesContext context, UIComponent component) {
        DataTable table = (DataTable) component;

        for(Iterator<DataTableFeature> it = FEATURES.values().iterator(); it.hasNext();) {
            DataTableFeature feature = it.next();

            if(feature.shouldDecode(context, table)) {
                feature.decode(context, table);
            }
        }

        decodeBehaviors(context, component);        
    }
}

2)Override SelectionFeature's decode

Updated: edited to allow deselecting

public class LazySelectionFeature extends org.primefaces.component.datatable.feature.SelectionFeature{

    @Override
    public void decode(FacesContext context, DataTable table) {
        String clientId = table.getClientId(context);
        Map<String,String> params = context.getExternalContext().getRequestParameterMap();

        String selection = params.get(clientId + "_selection");

        if(table.isSingleSelectionMode())
            decodeSingleSelection(table, selection);
        else
            decodeMultipleSelection(context, table, selection);
    }

    void decodeSingleSelection(DataTable table, String selection) {
            if(ComponentUtils.isValueBlank(selection))
                table.setSelection(null);
            else
                table.setSelection(table.getRowData(selection));
        }

    void decodeMultipleSelection(FacesContext context, DataTable table, String selection) {
        Class<?> clazz = table.getValueExpression("selection").getType(context.getELContext());
        boolean isArray = clazz.isArray();

        if(!isArray && !List.class.isAssignableFrom(clazz)) {
            throw new FacesException("Multiple selection reference must be an Array or a List for datatable " + table.getClientId());
        }

        if(ComponentUtils.isValueBlank(selection)) {
            if(isArray) {
                table.setSelection(Array.newInstance(clazz.getComponentType(), 0));
            }
            else {
                table.setSelection(new ArrayList<Object>());
            }
        }
        else {
            String[] rowKeys = selection.split(",");
            List<Object> selectionList = new ArrayList<Object>();

            boolean lazy=table.isLazy();
            if (lazy) {

            List<String> currentRowKeys = new ArrayList<String>(Arrays.asList(rowKeys));
            if (table.getSelection() != null) {
                List<Object> alreadySelected = (List<Object>) table.getSelection();

                for (Object object : alreadySelected) {//For deselecting
                    Object rowKeyFromModel = table.getRowKeyFromModel(object);
                    if (currentRowKeys.contains(rowKeyFromModel)) {
                        selectionList.add(object);
                        currentRowKeys.remove(rowKeyFromModel);
                    } 
                }                    
            }
            for (String key : currentRowKeys) {//For selecting  
                Object rowData = table.getRowData(key);
                if (rowData != null && !selectionList.contains(rowData)) {
                       selectionList.add(rowData);
                }
            }

        }else{

                for(int i = 0; i < rowKeys.length; i++) {
                    Object rowData = table.getRowData(rowKeys[i]);

                    if(rowData != null)
                        selectionList.add(rowData);
                }

            }

            if(isArray) {
                Object selectionArray = Array.newInstance(clazz.getComponentType(), selectionList.size());
                table.setSelection(selectionList.toArray((Object[]) selectionArray));
            }
            else {
                table.setSelection(selectionList);
            }
        }
    }
}

Might not be the best solution but should work, let me know if there is a better way. Hope this helps someone.

Problem

Original source