I like WODisplayGroups. OK, call me crazy – or lazy – but I like them alot. However, I do find that I often need more control over them than the drag and drop creation gives me. So here is how I like to set up WODisplayGroups programatcially:

Just to prevent any potential confusion: This example demonstrates creating a WODisplayGroup from scratch, and will not work if you’ve created one by dragging an Entity from EOModeler into WebObjects Builder. – Thanks Alex!

Using this pattern setup the _displayGroup object

protected WODisplayGroup _displayGroup;
 
public WODisplayGroup displayGroup() {
	if (_displayGroup == null) {
		prepDisplayGroup();
		find();
	}
	return _displayGroup;
}
public void setDisplayGroup(WODisplayGroup dg) {
	_displayGroup = dg;
}

Add the prepDisplayGroup() method:

public void prepDisplayGroup() {
	_displayGroup = new WODisplayGroup();
	_displayGroup.setNumberOfObjectsPerBatch(10); 
	EOSortOrdering asc = EOSortOrdering.sortOrderingWithKey(
			"keyToSortOn", 
			EOSortOrdering.CompareAscending);
	NSArray ordering = new NSArray(new Object[] {asc});
	_displayGroup.setSortOrderings(ordering);
}

The WODisplayGroup API is here

Finally add the find() method:

public void find() {
	NSArray foundObjects = //fetch your objects here
	displayGroup().setObjectArray(foundObjects);
}

In my find() method I usually take advantage of the objectsFor... methods that can be generated by EOGenerator. These wrap your EOModel’s fetchSpecs in static methods in your EO’s, very cool. Take a look at the EOGenerator EOGJavaSource.eotemplate for more details. Update: I’ve blogged more details about my EOGenerator templates here

I often base my search pages on a common super class that includes a displayGroup along with variables for setting objects per batch and a search string amongst other things.