Re: [PyPerSyst-Devel] Surrogates and nested entities

[<po...@or...>]

Peter Lyons <pe...@pe...> writes:

>  >>Yes, and recursively creating surrogates for all nested entity
>  >> instances in the graph.
> 
>  >No nesting.  Nesting is evil.
> 
> So let's say I have a Person entity with two fields that are Address
> Entities, homeAddress and workAddress.  Let's say I display this info
> in a web form and the user edit's the person's name and part of each
> address.  How many UpdateSurrogates would I need to create to get this
> transaction through the system? I'd like to do (pseudo code):
> --------
> surrogate = realPersonRef.getUpdateSurrogate()
> surrogate.firstName = newFirstName
> surrogate.homeAddress.postalCode = newPostalCode
> surrogate.workAddress.state = newState
> 
> engine.execute(surrogate)
> --------

A use case is good.  The example you give is not what I consider
evil.  I'm not completely sure yet how to handle attributes of
references.  I have to give more thought to this.

> (actually, I prefer accesing attributes by methods always, but this
> is just a for-instance)

Why is that?  Sounds like needless overhead to me.

> Would I need to do 3 calls to getUpdateSurrogate() or some similar
> method?  I prefer it when there is no distinction between editing a
> "leaf" object or a "branch" object.

I agree that there shouldn't necessarily be a distinction.  There
isn't on read access.  Making changes, however, is different.  I need
to work through some examples to figure out the best way to handle
this.  Sometimes a group of changes like this may actually logically
be three separate transactions.  So then it is a question of how to
simplify the creation of all three.  Other times the group of changes
might represent a single transaction (changes to an order and order
details).  Off the top of my head it sounds like if the relationship
is a composition (like order and order detail) then the changes would
represent a single transaction.  If not, the changes represent
separate transactions.

Good questions.  Much to think about.  ;-)

-- 
Patrick K. O'Brien
Orbtech      http://www.orbtech.com/web/pobrien
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