Good answer. Also be careful with how you define OO object identity. Some ORMs cache in-memory objects (eg: lookup by id) and determine if an object is the same

Good answer. Also be careful with how you define OO object identity. Some ORMs cache in-memory objects (eg: lookup by id) and determine if an object is the same through equals() implementation and hashCode(). IMHO ORMs are nice if you use a OO heavy language, and want to reuse ORM classes in your domain and/or as DTOs. The biggest gotcha is that you will have to understand the quirks of the ORM (N+1, lazy, object equality, eager vs. lazy, types of inheritance, pk generation, integration with legacy DBs, polymorphism, etc). Some legacy DBs make it very hard to integrate with an ORM (eg: no PK, Composite PKs with weird PK generation, etc).