How to implement GWT editors for subclasses of a type?

Question

Let's say I have an object hierarchy like this:

Account > Site > Supply

An Account is an actual company, a Site is a building they have, and a Supply is either an ElecSupply or GasSupply. Supply is never instantiated and could be an abstract class in theory.

I am using Objectify for persistence, and have a page that displays the list of Supplies for each Site, regardless of whether they are an ElecSupply or GasSupply.

Now I am implementing the GWT Editor Framework and have come up against a problem with this polymorphic entity. How do I implement an Editor and set of sub-editors for an object like this?

@Entity
public class Supply implements Serializable
{
    @Id
    protected Long id;
    @Embedded
    protected List<BillingPeriod> billingPeriods = new ArrayList<BillingPeriod>();

    public Supply()
    {

    }
// ...
}

The subclasses: (ElecSupply has 5 unique fields and GasSupply has just one)

@Subclass
public class ElecSupply extends Supply implements Serializable
{
    private String profile;
    private String mtc;
    private String llf;
    private String area;
    private String core;

    public ElecSupply()
    {

    }
}

---

@Subclass
public class GasSupply extends Supply implements Serializable
{
    private String mpr;

    public GasSupply()
    {

    }
// ...
}

So I would like to know if anyone has any experience with this kind of structure? I have tried to make separate editors for ElecSupply and GasSupply, and then show or hide them as part of the edit page.

The other way I was thinking about doing it would be to have a single editor (for Supply), and then load different sub-editors depending on which type of object we are editing.

Any light shed will be gratefully received.

Farman

Answer 1

I've already been in this case, and I've implemented the following solution :

• First create an generic utilitary class named AbstractSubTypeEditor which will activate a specific editor when you edit one of your subclass object :

  import com.google.gwt.editor.client.CompositeEditor;
  import com.google.gwt.editor.client.Editor;
  import com.google.gwt.editor.client.EditorDelegate;
  import com.google.gwt.editor.client.LeafValueEditor;
  
  public abstract class AbstractSubTypeEditor<T, C extends T, E extends Editor<C>> implements CompositeEditor<T, C, E>, LeafValueEditor<T> {
          private EditorChain<C, E> chain;
          private T currentValue;
          private final E subEditor;
  
          /**
           * Construct an AbstractSubTypeEditor backed by the given sub-Editor.
           *
           * @param subEditor the sub-Editor that will be attached to the Editor
           *          hierarchy
           */
          public AbstractSubTypeEditor(E subEditor) {
                  this.subEditor = subEditor;
          }
  
          /**
           * Returns the sub-Editor that the OptionalFieldEditor was constructed
           * with.
           *
           * @return an {@link Editor} of type E
           */
          public E createEditorForTraversal() {
                  return subEditor;
          }
  
          public void flush() {
                  currentValue = chain.getValue(subEditor);
          }
  
          /**
           * Returns an empty string because there is only ever one sub-editor used.
           */
          public String getPathElement(E subEditor) {
                  return "";
          }
  
          public T getValue() {
                  return currentValue;
          }
  
          public void onPropertyChange(String... paths) {
          }
  
          public void setDelegate(EditorDelegate<T> delegate) {
          }
  
          public void setEditorChain(EditorChain<C, E> chain) {
                  this.chain = chain;
          }
  
          public void setValue(T value, boolean instanceOf) {
                  if (currentValue != null && value == null) {
                          chain.detach(subEditor);
                  }
                  currentValue = value;
                  if (value != null && instanceOf) {
                          chain.attach((C)value, subEditor);
                  }
          }
  }
  

• Now you can create an Editor for Supply, containing two sub-editors and two AbstractSubTypeEditor (one for each of your subtypes) :

  public class SupplyEditor extends Composite implements Editor<Supply> {
  
          public class ElecSupplyEditor implements Editor<ElecSupply> {
                  public final TextBox profile = new TextBox();
                  public final TextBox mtc = new TextBox();
                  public final TextBox llf = new TextBox();
                  public final TextBox area = new TextBox();
                  public final TextBox core = new TextBox();
          }
          @Ignore
          final ElecSupplyEditor elecSupplyEditor = new ElecSupplyEditor();
          @Path("")
          final AbstractSubTypeEditor<Supply, ElecSupply, ElecSupplyEditor> elecSupplyEditorWrapper = new AbstractSubTypeEditor<Supply, ElecSupply, SupplyEditor.ElecSupplyEditor>(elecSupplyEditor) {
                  @Override
                  public void setValue(final Supply value) {
                          setValue(value, value instanceof ElecSupply);
                          if (!(value instanceof ElecSupply)) {
                                  elecSupplyEditor.profile.setVisible(false);
                                  elecSupplyEditor.mtc.setVisible(false);
                                  elecSupplyEditor.llf.setVisible(false);
                                  elecSupplyEditor.area.setVisible(false);
                                  elecSupplyEditor.core.setVisible(false);
                          } else {
                                  elecSupplyEditor.profile.setVisible(true);
                                  elecSupplyEditor.mtc.setVisible(true);
                                  elecSupplyEditor.llf.setVisible(true);
                                  elecSupplyEditor.area.setVisible(true);
                                  elecSupplyEditor.core.setVisible(true);
                          }
                  }
          };
  
          public class GasSupplyEditor implements Editor<GasSupply> {
                  public final TextBox mpr = new TextBox();
          }
          @Ignore
          final GasSupplyEditor gasSupplyEditor = new GasSupplyEditor();
          @Path("")
          final AbstractSubTypeEditor<Supply, GasSupply, GasSupplyEditor> gasSupplyEditorWrapper = new AbstractSubTypeEditor<Supply, GasSupply, SupplyEditor.GasSupplyEditor>(gasSupplyEditor) {
                  @Override
                  public void setValue(final Supply value) {
                          setValue(value, value instanceof GasSupply);
                          if (!(value instanceof GasSupply)) {
                                  gasSupplyEditor.mpr.setVisible(false);
                          } else {
                                  gasSupplyEditor.mpr.setVisible(true);
                          }
                  }
          };
  
          public SupplyEditor () {
                  final VerticalPanel page = new VerticalPanel();
                  page.add(elecSupplyEditor.profile);
                  page.add(elecSupplyEditor.mtc);
                  page.add(elecSupplyEditor.llf);
                  page.add(elecSupplyEditor.area);
                  page.add(elecSupplyEditor.code);
                  page.add(gasSupplyEditor.mpr);
                  initWidget(page);
          }
  }
  

This should show/hide your fields according to the subclass you are editing, and bind the properties to the good fields.

Radbourne

Answer 2

You can have your SupplyEditor implement ValueAwareEditor<Supply>.

This way, the editor framework will pass you the actual value being edited in the setValue(Supply supply); In the implementation of setValue(Supply supply) you can inspect the type of Supply and choose to show/hide any additional relevant fields.

Journeywork

Thanks for the help. I am trying this but GWT is looking for the getters for profile, mtc, llf, area, core and mpr fields in Supply, when they are in the subclasses ElecSupply and GasSupply. How do I get round this? – Farman

Ok, i see. Maybe OptionalFieldEditor will help you there ? – Journeywork