[fdo-internals] RFC15 posted

[Maksim Sestic]

Hi Orest,

Yes, that's another possibility (and much more elegent I guess). It also
resolves dictionary "refreshing", meaning - what and when triggers data
re-fetching upon dictionary elements collection. 

Let's see how it might work:

1) new class PropertyValueConstraintLookup (or
PropertyValueConstraintPickList, as Barbara proposed)
2) takes feature schema name as parameter
3) takes a source class/feature class name from 2) as parameter
4) takes Key property name from 3) for key data source
5) takes Value property name from 3) for value data source (can be same as
4) for that matter)
6) has a getter method returning... well... instantiated FdoReader instead
of a dictionary (?)
7) has GroupBy and SortBy optional properties being cast upon 3)
8) Throws an error if there're duplicate keys in 4) - acting as some sort of
proxy dictionary

There's also one tricky thing about such class - it's "persistancy" within
feature store when underlying data changes (4,5). In other words - it
doesn't represent a true constraint. Otherwise, it would probably make it
all too complex and resource-consuming to implement. For starters, let's
have a consumer developer keep track of underlying data versioning and
consistency.

Regards,
Maksim Sestic



Orest Halustchak wrote:
> 
> That's a good point about DictionaryElement, but before we dive into that
> one, I'm wondering about whether it would be used at all to define the
> constraint. If the constraint is defined based on data persisted in
> another class, don't we need just references to that other class and not
> an actual dictionary held in a structure in memory? Or ... are you
> thinking that the constraint can defined either way, an explicit
> dictionary attached to the property definition or a referenced dictionary
> in another class? Do we need both?
> 
> Thanks,
> Orest.
> 

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