I'm aware of the different approaches (mostly from reading Fowler's PoEAA), but currently we use an Active Record-style ORM with a few extra features (like Class Table Inheritance) and we haven't found any major issues with this approach. What was the worst case scenario you experienced with the 1:1 approach?

Over the past 5 years I've been in two projects using 1:1 ORM Active Record == business model base approach. One completely failed in part because of this, second is barely manageable, but I managed to save it by moving business code mostly to the outside of Active Record classes.

The problem I encountered in those projects is the mismatch between storage mental model and business mental model, which lead to explosion of crappy code (AKA technical debt). In particular:

1. the classes I need for business model may have initially mapped well to database tables, but over time they stop; business logic and model changes much faster than you'd like your DB schema to

2. since many things in AR can fire SQL queries, you have to keep in mind the workings of your database when doing almost every operation on your model; it's an abstraction leak

3. code shooting off SQL queries is randomly called from all over your codebase; it's harder to keep track of it and, if needed, optimize those queries

I like AR as a convenient API to get data from/to database, but given the point 1., I eventually learned to isolate AR layer as something below business model layer, so that the pattern is that business model is explicitly serialized and deserialized from database, instead of the database being coupled with the logic of your program.

Now I vaguely recall complaining about this before on HN and getting my ass handed back to me by someone who pointed out that these are all ORM n00b mistakes. I wish I could find that comment (pretty sure I noted the link down somewhere). Yeah, I admit - in those two projects I mentioned, we were all ORM noobs. So we've learned those lessons the hard way.

> Approaches like "let's inherit from ORM class and add business-related methods", in my experience, lead to total disaster.

I don't disagree, in fact I'd go further and say that data and logic should not be coupled, but this is the Active record pattern which is far from the only way to use an ORM, most ORM's won't even support this pattern by default.

Moreover this is a terrible pattern. I would never use an ORM like that. An ORM implemented using the DataMapper pattern is so much better.