I gave up on ORMs after a year or so (back around 2006) of ActiveRecord doing the "makes the easy even easier, makes the hard impossible" syndrome someone else mentioned.
Then a couple of years ago, I started playing with a DataMapper/Unit-of-Work ORM (Doctrine2, in PHP-land). My experience, writing a moderately sized warehouse-management application, has been very good.
In Doctrine, you don't write your schema/DDL. Doctrine does, based on your Entity and Association mapping. You write plain-old-PHP-objects, and then map their relations (in XML, annotations, or YAML). Doctrine reads and validates your data model, and generates DDL statements to create the schema. Big surprise: it creates pretty much exactly the same schema you'd expect. (And it will generate and manage migrations, too)
Unit of Work is a powerful pattern, too, especially for web apps. You just worry about updating entities in memory. The ORM then flushes them to the datastore in a single transaction at the end of the request (so, by default, you have a one-to-one mapping between http requests and transactions in the RDBMS).
Datamapper/UoW is probably overkill for CRUD stuff; that's where ActiveRecord shines. But it pays dividends when you're dealing with more complicated state-transitions on your underlying entities, and there are lots of cross-cutting concerns.
I read Jeff's article and the comments here with interest. My only experience with an ORM is Doctrine2 (about 2.5 years) , and I've never really hit any issues. Whenever I've needed to duck out using the ORM in an edge case, its only been a few lines of code and very undisruptive.
In a recent project I manually mapped a large sprawling ancient schema manually using Doctrine2, and still never hit any major blockers. The code just abstracts away over the cracks.
Does anyone have any real world example articles on where an ORM has totally failed, and why?
Then a couple of years ago, I started playing with a DataMapper/Unit-of-Work ORM (Doctrine2, in PHP-land). My experience, writing a moderately sized warehouse-management application, has been very good.
In Doctrine, you don't write your schema/DDL. Doctrine does, based on your Entity and Association mapping. You write plain-old-PHP-objects, and then map their relations (in XML, annotations, or YAML). Doctrine reads and validates your data model, and generates DDL statements to create the schema. Big surprise: it creates pretty much exactly the same schema you'd expect. (And it will generate and manage migrations, too)
Unit of Work is a powerful pattern, too, especially for web apps. You just worry about updating entities in memory. The ORM then flushes them to the datastore in a single transaction at the end of the request (so, by default, you have a one-to-one mapping between http requests and transactions in the RDBMS).
Datamapper/UoW is probably overkill for CRUD stuff; that's where ActiveRecord shines. But it pays dividends when you're dealing with more complicated state-transitions on your underlying entities, and there are lots of cross-cutting concerns.