Save and query dependent objects

[Sebastian Sastre]

Hi Carsten,

	try to evade using rational model if the ODB gives you the power to
prioritize the conceptual model. This in your example will be storig the big
root composed object just the way you designed it conceptually and
prototyped it in the image.

	The MagmaCollections will be needed when you have to manage lots of
objects. In your example if the building has 200 floors you may or may not
justify a magma collection for that. If I need to query I'll tend to index
them in a magma collection regardeless they are 100 or 100 thousand.

	If instead of your example you have car part's you will easily need
to query among 50 thousand instances. For sure they should be stored indexed
in a magma collection.

	As far as I know nothing stops you to have in other part of the odb
the cars that also refers (have in its instVars) lots of those parts. That
way you won both: the easiness of having all the parts indexed in a magma
collection (usually the only efficient approach in the relational world) and
the conceptual model of it's position in the "car space".

	I hope this helps,

	cheers,

Sebastian Sastre


> -----Mensaje original-----
> De: magma-bounces at lists.squeakfoundation.org 
> [mailto:magma-bounces at lists.squeakfoundation.org] En nombre 
> de Carsten Karkola
> Enviado el: Jueves, 22 de Noviembre de 2007 18:03
> Para: magma at lists.squeakfoundation.org
> Asunto: Save and query dependent objects
> 
> Hi,
> 
> I'm new to magma and I've read the docs in the swiki and 
> browsed the magma tests to get a basic understanding how to 
> work with it. In the FAQs I found an answer: "With the 
> standard dependency mechanism, dependents are not directly 
> connected, so they will not be persisted". What does this 
> mean? Lets say I have some classes:
> 
> Building
> Floor
> Room
> 
> A Buidling has floors and floors have rooms. As far as I 
> understand - if I save a building instance in magma, the 
> assoicated floors and there rooms will also be saved. So I 
> can get a building instance from magma and ask it  for its 
> children. But how do I look for a specific room in magma 
> without traversing the whole tree structure starting at the 
> building node. In a RDBMS I would query for the room - get 
> the foreign key of the floor and so on.
> 
> Or should I put all tree nodes (building, floor and room 
> instances) in there own MagmaCollection to use them with a 
> MagmaCollectionReader? What would be the best way to save 
> such a tree like structure with the ability to query for one 
> of the nodes and to get after that the parents of that node? 
> The goal is not only to traverse the tree from top but also 
> to answer questions like "What room has the user carsten and 
> in which building can I find this room?".
> 
> Thanks, Carsten
> 
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