Good Features for an ORM

Question

I'm currently working on putting together a fairly simple ORM tool to serve as a framework for various web projects for a client. Most of the projects are internal and will not require massive amounts of concurrency and all will go against SQL Server. I've suggested that they go with ORM tools like SubSonic, NHibernate, and a number of other open source projects out there, but for maintainability and flexibility reasons they want to create something custom. So my question is this: What are some features that I should make sure to include in this ORM tool? BTW, I'll be using MyGeneration to do the code generation templates.

Answer 1

For the love of all that's holy (and the women and the children), do everything possible to convince them not to go with a custom O/RM solution. Why are people wanting to re-invent the wheel when there are perfectly-good, open-source wheels already in existence?!?!

Answer 2

If your client isn't interested in OSS because of (real or imagined) perceptions about support, have you considered any of the top-quality commercial third-party ORMs such as LightSpeed that comes with a nice GUI designer tool

_{(source: mindscape.co.nz)}

Mindscape (the company that sells LightSpeed) is a New Zealand company based near where I live, I have met some of the devs there, and I know they are famous for having incredible customer support. And they give you the source code when you buy the software, so you can tweak it any way you like.

You probably don't want to have to roll your own ORM unless you have to and your client is willing to hand over a stupid amount of cash for you to do so.

Answer 3

IMO writing your own OR/M is one the worst design decisions you could ever make. "maintainability and flexibility" are reasons exactly NOT to write your own OR/M.

Please read See 25 Reasons Not To Write Your Own Object Relational Mapper, and see if your client really wants to pay what it costs to build something like NHibernate ($7.6M) or SubSonic ($1.5M). Because, like ChanChan said above, you will end up with something similar to that.