Re: Computed fields in Dexterity?

Sean Upton <[email protected]> writes:

> Is there any facility to do computed fields (similar to Archetypes) in
> zope.schema fields and z3c.form?
>
> I want to apply some kind of function (sum, average, etc) callable across
> other fields' respective values on the same form/context -- e.g. computed
> field_d = SUM(field_a, field_b, field_c).
>
> My only current constraint is that it be plone.supermodel-friendly
> (possible to serialize; maybe something syntactically similar to the way
> spreadsheets handle expressions).
>
> My sense is that there is not anything yet out there to do this?

You might be able to do something like this in the "invariant" part
of a "zope.interface.Interface". Its primary purpose is to verify
global interface conditions (relations among all fields in your case),
but I assume that you can also adjust such conditions (e.g. compute
field variables).

Note that your computed fields are not first class fields.
At the least, they must be "read_only". You might therefore
decide not to model them as fields at all but as properties
or "ComputedAttribute"s.


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