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Which ORM does fit best here?

I need to choose an ORM for a project and I only have some experience with NHibernate. I have been reading Q&A from StackOverflow, and the most similar to my needs is What ORM for .net should I use?, but I would like to have an answer more adequate to the present products (the link is from 2009) and that also take into account some points of my project.
The easiest solution for me would be to use NHibernate because it is mature, feature rich and I have already used it, but I prefer to choose the best option for the project even if I have to "study" again.
The project is going to start as a core that communicates with SAP. The core has to support standalone and/or co-dependent modules, and each one of them may need to work with its own data from the database. The final step will be to implement the part of SAP that we use. The characteristics I need are the ones from the previous link and here are some more things to have in mind:
I would like to be able to split the data access layer so that a user with one or two modules won't need the whole thing.
A designer would be appreciated.
It will start with about 20-30 tables and, within a couple of years, that number will grow in several hundreds.
The amount of registers per table will vary from two or three to 150000+ (very few).
IT DOES NOT NEED TO BE A ONE PRODUCT SOLUTION. Combinations like NHibernate and Devart Entity Develop are also welcome.
The team for this project will also have students that will have to learn C Sharp and some of them probably don´t know exactly what an ORM is, so it would be great if it is simple or, at least, the basic stuff is not very complex (mixing tons of lambdas, reflection, extension methods, etc.).
The last one is not very important. I hope this is specific enough to avoid been closed (the question I link is still open).
EDIT:
-It is a desktop application.
-Documentation and comunity are also very very important.

The most popular ORM for .Net these days is Entity Framework. It comes from Microsoft, so well documented in MSDN style. And it fits your criteria.
I worked with NHibernate and found that documentation is patchy, inconsistent and sometimes missing. Most of the time I had to use docs for Hibernate which were not for NHibernate, just similar.
EF can do the same things and more than NHibernate, and the latest release have Migrations, which was missing (when I worked with NHibernate).

Consider it Dapper: dapper-dot-net.
Dapper is a pretty simple ORM, developed and used by StackOverflow.
There is a lack of documentation, but that is because of it simplicity. You can find some usage example in the project page or in some websites like this.

I know this is a pretty old question, but I though I would post an answer for anyone who lands here. Check out SQL Data. It is extremely simple to use, very powerful and fits all the OP's requirements.

DataObjects.NET: a good (flawless, documented, support) ORM?

I am looking for ORM frameworks, came along to NHibernate, Genome, L2S, Entity Framework and now the DataObjects.NET.. So far a I read the documentation it seems pretty cabable, but have you ever tried this ORM?
Any issues/bugs with DO.NET would be approciated :)

I used DataObjects.Net v4.
It supports VS 2010 and .Net 4.0 and it is really good ORM.
It's easy to use and it constructs the database automatically so you do not design the database and reverse engineer it to classes like some other ORMs.
The only thing that was so annoying about it is the Session management and switching mechanism in case of web applications. I think even this is being taken care of in version 4.4 currently under development.

I think you should take a look at LLBLGen Pro as well. I think this is probably the best .NET ORM out there.

Aside from the fact that this question sound a lot like an informercial, there's a big problem with DataObjects.Net - it's dual-licensed as a GPL or commercial w/o evaluation. So the answer is - no, I have not tried it and it is quite unlikely I will try it.
I have no beef with GPL (though I do not like it for various reasons), or dual-licensed products - after all the license choice is a right to the copyright holder. However, I also want to reserve that right for my software as well. I am writing commercial software, which I have no problem releasing as open source, but under a license of my choice. If I am to adopt a new ORM, I want, nay - I need to be able to release a CTP preview of my product to a limited set of customers for real-life testing. And that would mean I either have to splurge the money for DO.Net upfront without knowing whether my investment will benefit me; or I have to release my sources under a license that effectively takes away the control over my app from me and has the potential to ruin my business by commoditizing my product.
Now, if there was a limited evaluation license, say one month noncommercial use, I might consider giving it a quick trial and see how it works.
If a product wants commercial adoption, it needs to have a risk-free way for early adopters to evaluate it.

Does DataObjects.NET support SQL identity columns yet? I abandoned v3 because I couldn't find a way to support identity columns.

Implementing C# Business Objects (CSLA)

We are about to commit to implementing Rocky Lhotka's CSLA as an application development Framework for our Visual Studio 2008 solutions. I would like to test the water on SO and am particularly interested in developer's opinions of the approach in comparison with other ORMs such as Entity Framework or nHibernate.
Also, what is the learning curve like and is it as easy (as I have heard) to maintain the applications written to this methodology?
Also would be very interested to hear from any Public Sector (especially Government Agencies) who have implemented this.
Thanks,
MaS

CSLA is not an ORM framework. It is a framework for implementing business objects. However, there are code generators available which can generate data access code for you. The CSLA framework is based on Active Record Pattern. This pattern will not scale for large scale project. In my opinion, you should implement a prototype. The goal of the prototype should be to:
Define a layering Scheme
Unit Testability of Classes
How the framework plays well with other framework
How it fits with other OR mapping tools
Learning Curve
If your evaluation seems to be positive against the above items, then go for it. In short, there should be a proper justification for using such a framework. You should not go with some one's advice, rather try it out by your own.

The learning curve of CSLA isn't too bad but be prepared to spend some time reading in the book. We have taken care of a lot of the learning curve for you by generating a DAL (Parameterized SQL or Stored Procedure support) for you, so it adds an ORM feel to CSLA only because it manages the DAL for you if you choose. But you can completely use it as just a set of BO templates. I find that active generation makes it much easier to upgrade to newer versions of CSLA as well as add functionality without having a strong need for an intermediate class.
Thanks
-Blake Niemyjski (Author of the CodeSmith CSLA Templates)

I love CSLA.
I used it to implement some ASP.NET 2.0 applications, some very large. It's easy to understand (after you understand Root, Child and Switchable objects), but you'll rely heavily on code generation (like CodeSmith).
Main question is: do you need CSLA? What feature do you like, or you just need to use some ORM? Today, I'm writing new applications with ADO.NET Entity Framework and it's more productive than CSLA.
Keep in mind CSLA isn't a metodology, but just a tool: you'll need to understand it and to tweak it when appropriate.

CSLA is a business object framework. There are many strategies for dealing with Data access - there is much overlap between ORM and data-access. I have had a lot of success using Linq-to-SQL in a Data Access Layer to simplify development. I think this is an approach that will work for you - especially given (based on your comments) your need to support both SQL Server and Oracle.
Using a seperate DAL is well documented in Rocky's book and samples on www.lhotka.net
As far as TFS - it's an ALM tool for Source Control, Project Managment and Build Automation. You would want to put the CSLA Source under source control like any other code. The simplest approach would be to include CSLA in your solution.
Another approach would be to compile it seperately and use a file reference in your projects to the CSLA.DLL. In TFS Automated build there is a property group which you could put the path to that DLL on your build server.
Lastly Rocky sells CSLA training videos on his website at http://download.lhotka.net/default.aspx?t=Core38

You can check Rocky's thoughts on SOA in the following broadcast:
http://www.slickthought.net/post/Minneapolis-Developer-Roundtable-Podcast---Talking-REST.aspx
The main thing you will need to grasp is that CSLA is a Business framework. Even though ORMs can give you basic validation (and other) features they do not IMHO really compensate for the lack of a solid business layer. You can of course use an ORM with CSLA (there is an example of using EF in the CSLA examples and NHibernate is used as an example in the CSLA Contrib project I believe) but the technologies are just complimentary.
The learning curve... well that depends on you. I found it quite easy to get started with. i think if you have a good grasp of OO you should be fine to get something basic up and running soon. The recent videos released are also very good to get yuo started.

Is it foolish of me not to use NHibernate for my project?

I am working on a .NET web application that uses an SQL Server database with approximatly 20 to 30 tables.
Most tables will be included in the .NET solution as class.
I have written my own data access layer to read the objects from, and write them to the database.
The whole thing is consist of just a few classes and very few lines of code en uses generics and reflection to find out what SQL and parameters to use.
Now, such thing could be done by using NHibernate (or similair framework) and some co-workers claim that is foolish of me not to use it.
My main argument for not using it is that i want maximum control over my application, know exactly what everything does and how everything works, even if that costs me more development time.
I also dont like the fact i have to map my database in XML files (my own solution lets me map it in the entity class files).
So, what i would like to hear from you is, is it really stupid to not use NHibernate in this situation?
Am i really being ignorant or is it not such a strange idea to use my own solution?

I think these days there really isn't any reason to roll your own persistence framework since there are so many good choices out there. You don't have to use NHibernate (though it is a good choice) but I would seriously consider using something that is well tested and established in the industry as it will tend to perform better and have less bugs that something you write yourself.

It probably is foolish to write your own classes instead of using NHibernate, but it's less foolish to continue using your own classes, given that you've already written them. Maybe.

I won't call you foolish because I've done exactly the same thing in the past. Then I started using NHibernate and wondered why the hell I rolled my own. It's good, give it a go.

You have several possibilities that are probably better than you reinventing the wheel. Let me name two most likely choices:
Use Entity Framework for your DAL+DAO. This will make your classes (that you've already written) obsolete, since EF will create their own and you'll get up to date with latest language capabilities and technologies.
Use Fluent NHibernate so you don't have to work with XML mappings. This way you'll keep your business layer object classes you've written and avoid tedious NHibernation XML files. It's all C#.
Your way of thinking is good. You want control. That's fine. But using your own DAL is a bit foolish these days, because you are basically reinventing the wheel, plus you'll have not tested/buggy code that will take considerable time to develop+test+debug.
If I were you, I'd go with the #2 option, since I've done option #1 and I know I had to customize lots of things to make EF work as it should. EF will be ready with V2.

People tend to use frameworks that are already written because, well, they're already written (and tested).
But there IS merit to rolling your own. Only you and your colleagues can make assumptions about your domain. A generic framework like NHibernate cannot make many assumptions, because that wouldn't make it very universal.
When you roll your own, you can bake these assumptions into your framework, to make a more streamlined, natural API. That said, if you were starting over I would have suggested taking an existing framework and wrapping it to better suit your needs. But since you already have something and it works for you, I'm not sure that I would suggest swapping it out for something else.

It depends on what they mean by "foolish."
If by "foolish" they mean you shouldn't have written your persistence layer in the first place, they're probably right, but that's crying over spilled milk.
If by "foolish" they mean you should rewrite all your existing code to use another framework (like NHibernate) when it's already working with yours, they're probably wrong (although there's something to be said for # of bugs in NHibernate vs likely # of bugs in yours).
If by "foolish" they mean the entire team knows NHibernate cold, and it's already used in the rest of your code, so by using your framework you're making it harder on the team, they're absolutely right, and you should probably refactor the code in NHibernate as soon as possible, before any more code gets locked in to your framework.
If by "foolish" they mean no one there really knows NHibernate, they just like it, then... nobody wins. They're being fussy, you implemented a framework you didn't have to... let's call it a tie.
All of that said, everyone should write a persistence framework or three. Those probably shouldn't end up in anything that ships, but it's a good exercise. The only mistake you made was tying code the team had to maintain into your good exercise.

There are many good persistence tools out there that are well tested and have proven performance (NHibernate, Linq to entities, LLBL Gen Pro). If your needs are very different from the normal persistence frameworks that exist then I would roll my own. I would want to take advantage of the testing and optimizations of an existing tool if at all possible, however.
That being said, I might also roll my own if I wanted to have the experience of building my own ORM tool and was willing to live with the downsides (not as well tested or optimized as tools that have been around for years, speed to market).

Making your own solution, especially when it seems to work fine and be as simple as you say, is neither ignorant nor strange. There are lots of situations where it's better to do that than to add a dependency on a separate project like nHibernate.
That said, there are of course also a lot of situations where the complete opposite is true. :)
It really depends on your project and team. If you are developing an enterprise application that will eventually be supported by someone else, sticking to industry standards might be a good idea even if it means a bit more work up front.

All of the answers here are great, but I am really surprised that nobody has mentioned Castle ActiveRecord, it sounds very similar to what your framework does and really simplifies the interface to NHibernate. It's one of the patterns that made Ruby on Rails so popular after all!
Ayende Rahien (one of the principal NH developers) gave a GREAT presentation on ActiveRecord at Oredev a few years ago which I highly recommend: http://www.viddler.com/explore/oredev/videos/89

I think that it is a matter of balance of control. You say that you want control and you don't want mappings. If this control comes at the cost that there is an increased development and maintenance cost and that it takes longer to produce working code, then it is a problem.
I personally don't see a problem in rolling a framework as long as it simplifies a repetitive task and makes development more productive and code more stable due to less room for interpretation. We have rolled our own framework, that includes a persistence/data access implementation. Our reasons for doing it, though, were specific. In this case, it was to work within a DDD environment that was much closer to what Evans describes than what most off the shelf products were providing.
I think the difference is, though, that we understood that there was an upfront cost and that it would eventually balance itself out through savings in development time in the future. Of course, if you are writing code that you manually have to manage connections, map data, etc., you are probably going down the wrong path. At the very least, you could be using something like Enterprise Library to help you manage the tedium of connectivity and command construction. But, I also think, that if you have no reuse - nothing that is a "framework" type of implementation that you can abstract and apply to other projects, then you are creating a maintenance nightmare and time sink that you will be the sole owner of.

We were also using our own Data Access Layer and entity classes. We also had a code generator who used to generate all this classes for us. But now we are using Entity Framework and we are more then happy.
Simple advise : Start learning nHibernate or whatever you prefer and start using it in your next project.

Entity Spaces - http://www.entityspaces.net/Portal/Default.aspx
is also a good tool.

I ended up using Fluent NHibernate for the job.
All my entity classes were generated with ActiveRecordGenerator (http://code.google.com/p/active-record-gen/)

Compare and Contrast NHibernate and OpenAccess from Telerik

Have you used the OpenAccess ORM from Telerik? How does it compare to NHibernate? When should I consider using it over NHibernate?

I'm wondering the same thing myself. On one hand, there's NH with its free, open-source self, but with limited support options. On the other, a fairly new addition to a well-known tool provider's box, OA.
OA costs money, but you get support. NH is free, but support has been known at least in my brief experience to be limited and slow in coming.
I think both are likely fine products. I've decided to give OA a try since I am already a user of Telerik's tools. OA and its support are being paid for anyway.
NH uses plain classes and object with no decorations on the class properties whatsoever. OA requires decorations (nicely generated by the OA Visual Studio GUI).
NH requires a "session" in which to do a unit of work with the database; OA calls it "scope". Both use "transaction".
OA has integration with Visual Studio and can both forward- and reverse-map to and from a database. Forward mapping is so you can design your classes and then "push" those into the database for persistence. The "reverse" is for you "domain model" developers which is what I prefer.
OA is definitely undergoing some major updates as Telerik plays "catch up" per its recent acquisition and release of OpenAccess, formerly owned by Vanatec (out of Germany).
As far as an "ease of use" and "performance / scalability" standpoint, I wish I knew where each stood. I'm sure someone out there could put together an honest test between the two and make those determinations.
One thing I like about NH is the available templates to generate the needed code not just for the "dumb" business objects (which is all OA generates now), but for a BLL and DLL. After much conversation with Telerik, I have the impression they plan for more code-generating options so OA is more useful out of the box.
Hope this helps! Someone please try to get some stats on the performance issues.

I've not used it but one benefit obvious to me, is OpenAccess is supported by Telerik, where as nHibernate is supported by the community. Depending on your company this can be a deciding factor if your ready to embrace open source solutions with no guarentee of support.
Edit
For the record I am a big supporter of nHibernate, and open source in general. I have been using nHibernate for the last six months, using it for all new work in our web application. For my current company it is a good fit (Startups love free).
However, my previous employeer, would have had a very difficult time accepting a community supported component as a core piece of their infrastructure. This is perfectly reasonable as these companies' web sites are their sole source of revenue. Would you want to stake your entire business on software that has no accountability associated with it? Some people wouldn't want to take that risk on.
Personally I have found the support for nHibernate to be on par and even better with some commercial vendors.
My point is not to bash OSS, but to highlight one benefit of using software that has a coporate backing, with a fully staffed and dedicated support channel.

One more reason: Currently OpenAccess has better performance characteristics, if you need fast ORM for your project it will be a better choice. See ORM benchmarks for details.

I would say nHibernate is free and OpenAccess is $399. Although CodeSmith with nHibernate templates is $99-$399 if you want nHibernate easily automated. It looks like OpenAccess has more transparency in the data layer and is probably easier to maintain. But, if you used something like Spring.Net you would not only have nHibernate automating the data but the service layer automated as well. Although take that with a grain of salt because nHibernate and Spring.Net are another batch of configuration files that need to be maintained. I bet OpenAccess is GUI friendly. Either one works, but there is alot more info out there on nHibernate.