[news.eclipse.modeling.gmf] Shortcut for 1:1:n containment reference cha

[Christian Muth <c.muth@xxxxxx>]

Hi all,



Few days ago, I asked another question here on the group: "ListLayout in 
compartments not working as expected".

After some investigation and playing around, i found a solution to my 
original question, although the actual problem is titled differently.


To make explanation easier, let's assume my domain model is as follows:

1 :  1 :  0..n
A => B => C
       => C
       => C

So one A owns exactly one B which in turn owns several Cs.

In my example, the core of the problem with my node mapping for A was 
that i had to use a rectangle inside A's compartment (for node mapping 
of B although not showing anything). One can't directly place 
ChildReferences of C into NodeMapping of A, a NodeMapping for B is 
necessary to hold the ChildReferences:

NodeMapping A
  ChildReference A.b : B
     NodeMapping B
        ChildReference B.cs : C
etc.

Rectangle B in turn should have been the container for the children C 
and should have grown to A's compartment dimensions, but Cs should be 
placeable freely inside B. B does not have attributes to be displayed 
though.

I couldn't figure out how to get this behavior so i started a different 
approach:

I solved this issue by creating kind of "shortcuts" in my EMF domain 
model so that i can ask A for instances of C. (containment, derived, 
transient references from A->C) - Remember: A->B is 1:1 containment 
reference. These references have to be containments to be selectable in 
.gmfmap.

The implementations for these derived features in EMF's AImpl.java 
simply forward to C's getter methods:

in AImpl:
/**
 * generated NOT
 */
public EList<C> getCs() {
  return this.getB().getCs();
}

So the domain model doesn't get screwed up.


To get this working, I needed a Feature Seq Initializer on the 
NodeMapping of A which creates the B instance on the fly when an A Node 
is created in the diagram. Generated initialization code for this goes 
into ElementInitializers class.

So i was able to remove standalone Figure Descriptor for Rectangle B and 
its Node definition completely - instead i created a Rectangle inside 
Rectangle A, created a ChildAccess for that inner Rectangle and used it 
in A's compartment "Accessor" property.

Now i placed a BorderLayout into Rectangle A, put BoderLayoutData 
(BEGINNING, vertical=true) as child into A's Label and created a 
BoderLayoutData (FILL, vertical=true) inside A's inner Rectangle (which 
is the compartment rectangle).

Now it works as desired & A's compartment's contents (which are XYLayout 
due to ListLayout=false in .gmfgen) are also layouted well by the 
"Arrange All" feature.


So my problem comes down to the fact(?) that you need to reflect your 
model's containment hierarchy in the .gmfmap and that one isn't able to 
shortcut the A->B 1:1 containment references so that the ChildReference 
of C can directly be placed inside A.

I have lots of these 1:1 containment references like A->B in my domain 
model, with B not only having one but many referenced types like C. I 
also have many occurrences of

A -> B -> C -> D
1 :  1 :  1 :  n

It would really be quite a painful task to address this issue with the 
workaround described here: shortcutting these containment hierarchies 
from A -> D.

Might it eventually be possible to extend GMF to support this? If so, 
could someone with more experience in GMF please point me to the places 
to look/modify? Or does GMF already support this?

If this might be useful for others as well, I would prefer sharing my 
solution back to the community.


Cheers

Christian