What is so great about ORM?

Question

So I'm having a head against the wall moment and hoping somebody can come help either remove the wall or stop my head from moving!!

Over the last 3/4 weeks I've been investigating ORM's in readyness for a new project. The ORM must map to an existing, large and ageing SQL database.

So I tried Subsonic. I really liked v2 and v3 after modding to work nicely with VB and named schemas in SQL was running OK. However, its lack of flexibility of having separate entity properties names vs column names had me pulling my hair out (sorry Rob).

I tried Entity Framework but I found like others it lacking in certain areas.

So I bit the bullet and tried nHibernate but after a week or so getting it working how I liked (with help from Codesmith to generate classes/hbms for me) I'm frustrated with the time it takes to startup (build a config object), despite trying a number of tricks to reduce this time.

I'm essentially after building a DAL class that I can share between apps and websites. Am I barking up the wrong tree? For a legacy project with 100s of tables should I go back to ado.net and use DTOs? Aarrgh!

Sorry for the ranty style of question. I don't have much hair left and I'd like to keep what I have!!

Thanks in advance, Ed

PS. I should add that I know SQL very well and not scared of getting my hands dirty to write fast queries. If anything I don't need to be hid from SQL

Absorbent

What kind of app do you have so that nhibernate startup time is an issue? IMO, it should only bother you if you directly access DB from desktop, not in case of a middle-tier service. – Godhood

You could simplify this rant quite a bit by simply asking "How do I speed up an NHibernate application's startup time?". – Particia

Andre - I am looking to use NHibernate from the desktop! As part of a class library that will be referenced by a number of helper apps. Some of these small apps take seconds to run, no problem using traditional ado.net approach but painful using NHibernate – Absorbent

Michael - I've tried both suggestions - placing all mappings in one hbm file and binary serialization of the hbm. Both make improvements but there is still a noticeable lag. – Absorbent

Answer 1

ORM let's you:

1. To map table rows to objects, that are the the workable pieces of object oriented programming.
2. To automatically navigate through object relationships
3. To easily add, edit and remove table rows
4. To query the database in a more intuitive way as you don't have to think of joins (this one will depend on the ORM and the query method)
5. To transparently handle L1 and L2 cache.

All of the above would have to be handled by hand if you werent using ORM.

PS: I agree to Dmitry as to the startup time of NHibernate (see question comments). Besides, did you try Fluent NHibernate? Fluent NHibernate is impressively easy. I couldn't believe my eyes when I first mapped a database. It's even easier than proprietary ORMs like DevExpress XPO.

Shoemake

+1 for recommending FluentNHibernate. Currently using it on a project and it really is "impressively easy". – Richerson

Answer 2

The biggest benefit of an ORM tool is that it will help you layer your application correctly. Most project nowadays use a Data Layer to connect to the database. You start from the ORM tool to produce classes that correspond to your database objects. Then you define an interface using these methods. All persistence code uses the methods of this interface. This way the business logic layer is only coupled to this higher-layer interface and needs to know nothing about the database. In fact there should be no dependency on ADO.NET or even NHibernate.

Another advantage of ORM tools is that you de-couple your application from the database server. You could change the db engine and still use the same code. Also there isn't only the complexity of the SQL that the ORM hides from you. It can also help you with transactions logic and connection pooling.

I'd say that for new projects an ORM tool is a necessity. For legacy projects it isn't so much beneficial, unless of course you have the time/money to start from scratch.

Wag

+1 for emphasis on decoupling. This alone is the reason I strongly advocate ORM tools and utilizing the repository pattern. – Atomy

ORM tools do not help with decoupling. Presentation logic can still use ADO.NET or SQL through ORM mechanisms to talk to the database. LinqToSql wants to be your business layer and actually makes it tricky to separate business and data logic. In most cases ORMs can't hide any SQL from you other than very basic CRUD and lookup by name/id type of queries. ORMs can be useful for legacy projects and don't always make sense for new projects. – Particia

ORM tools do help with decoupling. As I wrote, this is not the only thing you need to do, as you still need to define interface methods, which will hide dependencies on the ORM libraries. These methods can use however classes like 'Customer' or 'Order' that have been created with the ORM tool and map to the database. – Wag

Answer 3

In my experience, most ORMs end up being way more complex than SQL. Which defeats the entire purpose of using them.

One solution I'm enthusiastic about is LINQ2SQL. It excels as a thin layer about stored procedures or views. It's really easy to use and doesn't try to hide SQL.

Arratoon

I can sympathize with the issue of complexity; most ORM tools are fiendishly complex to configure. I would argue that they do solve a significantly complex range of problems to justify their complexity, and that the value gained in using them outweighs to penalty of learning how to use them. – Atomy

Andomar: ORMs, in general, are exposing objects, not SQL. That is the whole point. Why are you using an ORM if not to map relational tables onto objects? Maybe ADO.NET is more suited to your needs. – Particia

Andomar: Have you looked @ PLINQO? I mapped the same database with it and Codesmith and ended up with less errors and far faster execution time - no startup delay out of the box. – Absorbent

..but with some nice additional ORM bits that you don't get with plain Linq2SQL – Absorbent

Answer 4

There are basically two questions here:

What's great about ORMs? There are similar questions on Stackoverflow. See:

• What are the advantages of using an ORM?
• Is everyone here jumping on the ORM band wagon?

How can I improve NHibernate startup time? See:

• http://ayende.com/Blog/archive/2007/10/26/Real-World-NHibernate-Reducing-startup-times-for-large-amount-of.aspx
• http://nhforge.org/blogs/nhibernate/archive/2009/03/13/an-improvement-on-sessionfactory-initialization.aspx

Mate