Hi Matthias,
(form NIL
(gui '(+Chart) 3)
(table NIL NIL '((NIL F1) (NIL F2) (NIL F3))
(do 4
(row NIL
(gui 1 '(+TextField) 25)
(gui 2 '(+TextField) 25)
(gui 3 '(+TextField) 25) ) ) )
This looks correct.
If I understand the examples, I can connect the TextField with a +E/R
prefix class to a relation
Right. The chart by itself can only handle a two-dimensional data
structure, i.e. a list of lists. Each row of the chart is filled with a
sublist, and the chart takes care of displaying the data, accept changes
and store them in the list of lists, scroll the contents, and so on.
So the chart must be given such a list of lists. It doesn't know
anything about the database or objects.
but how do I select the correct object? Do
I have to loop over all objects or does the chart do that for me?
As you observed, the +E/R class can do that. It connects a relation of
an entity to a GUI component, and says: Handle this relation for me.
How this exactly looks like depends very much on your actual situation.
If that relation is already a list of lists, i.e. a (+List +Bag)
relation, there is not more to do. In other cases you can pass
additional 'put' and 'get' functions to the +Chart, to have the
automatic conversions to/from the two-dimensional representation done
for you.
At other times, you don't connect the chart itself to an +E/R, but pass
it a list generated separately (e.g. as the result of a database search,
as is the case in the search dialogs). Typically this is done with
'+QueryChart', a subclass of '+Chart', which does the searching via a
Pilog query.
As you see, this is hard to explain without a concrete example.
Perhaps you can show where you got stuck at the moment?
Cheers,
- Alex
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