Re: [boost] [rdb] 0.04

Subject: Re: [boost] [rdb] 0.04
From: Jean-Louis Leroy (jl_at_[hidden])
Date: 2009-09-21 19:46:51

> that means that a user would have to manually define the tables his objects 
> should be mapped to.
> [snip]
> so an o-r mapper must be able to dynamically create columns, and even remove 
> columns, as there can be > 1 NVPs with the same name, so the column has to be 
> moved to it's own table and mapped as a 1:n relationship. (STL container 
> again)

I have seen two philosophies wrt orm: with or without a description 
(call it "schema", meta-data or whatever) of the objects to be mapped. 
Tangram uses a schema and it creates the tables for you (see 
http://tangram.utsl.gen.nz/docs/Tangram/Tour.html#creating_a_schema). In 
the Perl world you have several modules of both type.

The advantage of schema-less tools is that they are very easy to use 
(just throw objects at them). Schema-based tools otoh give you 
predictible behavior and known database schemas (i.e. that don't depend 
on the particular set of objects that have ben stored) that you can get 
past your average db admin ;-)

I have used a predecessor of Tangram to store a representation of the 
Belgian Justice. It had 400+ business classes with many levels of 
inheritance and complex relationships. I doubt that a 
create-the-db-as-you-go tool would have cut it. OTOH there are many 
situations in which schema-based tools are overkill.

J-L