On 5/7/07, Spider <[EMAIL PROTECTED]> wrote: > > I'm fairly new to this, and trying to understand the ORM relationship > between a class and a table row. In most of the examples in the > documentation, there is a one-to-one relationship; a class instance > corresponds to a row of a table. > > In my application, my data falls into a 3-tier structure, represented > by tables A, B and C. Each A has zero or more Bs, and each B and zero > or more Cs. So, A->B is one-to-many, and B->C is one-to-many. > > >From an application perspective, the only type of entity is a "A", the > only reason I have Bs and Cs is that SQL tables cannot have repeating > columns (my previous database experience is with a non-SQL database > that allows repeating data items!). I think of the Bs and Cs as just > part of the particular A to which they belong.
*If* I understood your point correctly (sorry if it's not the case), I think you are looking for one-to-many relationships to the object itself. This can very well be done. Just remember a one-to-many relationship from A to B is expressed in your table as a foreignkey from B to A ! http://www.sqlalchemy.org/docs/datamapping.html#datamapping_relations_onetomany > > Now, in Python I can represent all the data for a particular A (ie A+B > +C) together in one item, say a nested dictionary. A nested dictionary will probably be quite hard to do with SQLAlchemy alone. > My question is, can the SQLAlchemy ORM do this for me - i.e. have a > single class A which maps to my 3 tables A,B,C and "knows" how they > are joined? If so, what should my class and table declarations look > like (and for bounus points, can I specify the declaration using > Elixir). In elixir, what you asked above (again assuming I understood what you wanted) would translate to: class A(Entity): has_field('name', String) # or whatever fields has the table ... belongs_to('parent', of_kind='A') has_many('children', of_kind='A') -- Gaëtan de Menten http://openhex.org --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To post to this group, send email to sqlalchemy@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en -~----------~----~----~----~------~----~------~--~---
