Re: Finally which ORM tool?

AliRezaGoogle wrote:
Hi
Currently there are some good ORM tools like NHibernate and LLBGL.
Microsoft is working on it's own one ( I think it's name is
EntitySpace) but not released yet.
I want to know members idea about selecting one of these ORMs:

--Should we wait untill Microsoft release his own ORM? ( and maybe
after two or three years again releases another one and we have to
throw our experiences away and styart to learn new one?)
--Choosing current ORMs is nice? (Does for example NHibernate remain
with .NET forever with support? What about future release of .NET? Is
there any quaranty that future features of .NET remain compatible with
current ORM frameworks? )

I'm almost universally not happy with any of them to be honest... but that's because I'm developing WCF web services and the only framework that I've tried so far, which is built with n-tier in mind, was netTiers - which I don't like because it's a code generation framework (meaning it builds all your business objects for you and then rebuilds these every time you make a changes to the databases... implying you can't modify your business classes to support IMyInterface or anything like that, making polymorphism often very difficult to use).

Otherwise I've used both DevExpress XPO and nHibernate. XPO is much slicker in terms of generating and maintaining the underlying databases and also has much better multi database support than nHibernate (which chokes when doing simple stuff like using Guid fields with MS Access). XPO also has a much more logical Attribute design since the nHibernate attributes are basically a hack wrapper around an XML mapping document (in fact, the attributes in nHibernate are simply used to generate an XML document on the fly in memory, which is then used to generate the object map). In XPO, as a consequence, you generally have to use far fewer attributes (sometimes none, on a persistent class, other times just one - for the class itself) and you don't have to worry about work arounds to the inherently hacky nature of the attributes in nHibernate (such as the fact that you have to give each attribute an "Order" parameter to specify the order in which it should be processed - attributes shouldn't have an order... they're meta data not logic).

Either of the above frameworks (nHibernate and XPO) are pretty good all in all. But neither of them do n-tier at all well. Both of them depend on the idea of "Sessions" and presume that you've got long lived sessions that last the lifetime of the application and REQUIRE you to save an object using the same session that it was loaded in (something that will almost never be the case when doing n-tier). They also both pretty much depend on the concept of lazy loading in order to decide what needs to be loaded and what doesn't... something that doesn't work at all when you're doing n-tier since the object and everything you need to know about it needs to be streamed across to the client and the session closed BEFORE you know what properties of the object the client is interested in. Finally, both nHibernate and XPO require you define the relationships between different classes if you want to create queries joining those classes and ONLY let you join those classes in your queries using the relationships that you defined using foreign keys... so no ad-hoc query joins (not without resorting to writing your own Views in the underlying database engine that you're using and mapping these to a persistent nHibernate/XPO class).

All in all the move to an ORM has been a bit of a mixed blessing for me in n-tier. I can see for plain vanilla desktop applications that none of the above would really be issues and both of the above frameworks would be huge time savers, but in n-tier you're going to spend about a month working around their various issues before either of them are usable.

Best Regards,

James Crosswell
Microforge.net LLC
http://www.microforge.net
.

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