Why is ORM considered good but “select *” considered bad?

Question

Doesn\'t an ORM usually involve doing something like a select *?

If I have a table, MyThing, with column A, B, C, D, etc, then there typically would be an object, MyThin

Answer 1

People use ORM's for greater development productivity, not for runtime performance optimization. It depends on the project whether it's more important to maximize development efficiency or runtime efficiency.

In practice, one could use the ORM for greatest productivity, and then profile the application to identify bottlenecks once you're finished. Replace ORM code with custom SQL queries only where you get the greatest bang for the buck.

SELECT * isn't bad if you typically need all the columns in a table. We can't generalize that the wildcard is always good or always bad.

edit: Re: doofledorfer's comment... Personally, I always name the columns in a query explicitly; I never use the wildcard in production code (though I use it when doing ad hoc queries). The original question is about ORMs -- in fact it's not uncommon that ORM frameworks issue a SELECT * uniformly, to populate all the fields in the corresponding object model.

Executing a SELECT * query may not necessarily indicate that you need all those columns, and it doesn't necessarily mean that you are neglectful about your code. It could be that the ORM framework is generating SQL queries to make sure all the fields are available in case you need them.