I wasn't talking about the MVC model, I was talking about the ORM. The ORM is the problem here not the MVC model :)
What do you perceive is the problem with an ORM in this instance? Lets assume for a moment that we disregard very simplistic solutions which crudely map database rows to objects
It seems very logical in this instance to have objects like Person "has many" Invoices "has many" LineItems (which) "belong to" Parts (which has several subclasses)
I don't immediately see that this is likely to be the performance bottleneck for any normal installation (I'm sure that there are corner cases)
The benefits are quite significant though and it makes it so much simpler to package up the business logic and test it
I suspect that if you look at your perceived design that you will find that you are likely already doing something like the above, just slightly differently...?
Regards Ed W