So, why should you use any O/R mapping tool? I am not talking about a specific tool but rather all O/R mapping tools in general.

There are a number of reasons for using an O/R mapping tool but before I dive into that, let me give you a brief overview of what an O/R mapping tool really is.
An O/R mapping tool generates persistence objects for your .NET application. It is a modeling and code generation tool that connects to your database and reads its schema, then lets you map objects to database tables and views, specify single-row insert, update, load, and delete operations, queries and stored procedure calls, as methods to these objects. And, it also lets you define one-to-one, one-to-many, many-to-one, and many-to-many relationships between objects based on relationships between tables in the database. It then generates fully working persistence objects code for you.
There are many other features that a good O/R mapping tool provides but I’m keeping my description brief so I can talk more about the benefits.

Reason 1: Cuts down your development time

First benefit of an O/R mapping tool is that it saves you a ton of development time (20% to 50% time depending on your situation). Now, O/R mapping tool is not generating any “rocket science” code for you and you could definitely do it manually if you wanted. But, this is a lot of tedious work and you would definitely be happier if you didn’t have to do it yourself. Let’s do some simple math.
A typical application with 15-20 database tables has 30-50 objects (including domain and factory objects) and this is roughly 5000 to 10,000 lines of code. It is likely to take you a few weeks to a couple of months to develop and test this code. And, if your application has more tables than this (which many do), then just multiple the above numbers by that much.
On the other hand, an O/R Mapping tool would generate this code for you in a day or two. Even here, you need these 1-2 days primarily to determine your object mappings to the database. The actual code generation is instantaneous. So, your time saving is tremendous.

Reason 2: Produces better designed code

Second benefit of an O/R mapping tool is that it lets you produce better designed code than doing it yourself by-hand. I know what you’re thinking. You think you can do a better job than an O/R mapping tool because you write every aspect of your code. Some of you definitely can but not everyone. Consider this. An average development team has different levels of expertise and experience and not everybody is a good designer. As a result, they may not follow design patterns in their code and end up with a lesser quality code. And, if multiple developers are writing code, their code is very likely going to be inconsistent with each other. And, inconsistency itself is a big source of poor quality in an application’s code.
On the other hand, a good O/R mapping tool uses code templates that have excellent design because they are very likely designed and created by very senior (architect level) engineers. And, these code templates almost always follow known design patterns. So, the code that you’ll generate from an O/R mapping tool is very likely going to be better designed than code designed by your own development team.

Reason 3: You don’t have to be a .NET expert

Third benefit of using an O/R mapping tool is that you don’t have to be a .NET expert to develop your persistence code. As you know, data access code is critical for the overall performance of your application. If this code is designed and developed poorly, it can severely affect your application. So, if you developed this code by hand, you need to be an export of .NET, COM+, stateless components, and MTS.
However, if you use an O/R mapping tool, you can focus primarily on the “logical design” of your persistence objects including object mapping and the different types of interactions with the database including insert, update, load, delete, queries, stored procedure calls, relationships, and more. And, the O/R mapping tool would do the rest for it. It would ensure that the generated code follows all the best practices of writing stateless .NET components to run in COM+ and MTS.

Reason 4: Saves you testing time

Fourth benefit of an O/R mapping tool is that it reduces your testing effort dramatically. If you developed all the persistence code by hand, you would also be responsible for testing it yourself. And, as you know, testing is as much effort as development in any project.
On the other hand, if you generated code from an O/R mapping tool, it is coming from code templates that are very likely thoroughly tested by the software vendor itself (more so than you because it is their primary focus). And, on top of it, most likely hundreds or perhaps thousands of other customers are using this tool and have tested the code generated from this O/R mapping tool. As a result, many of the bugs that you might not find in your own testing have already been found and fixed in the generated code of an O/R mapping tool.

Reason 5: Simplifies your .NET development

If you have to write all the persistence code yourself, you’re bogged down into the details of ADO.NET, COM+, MTS, stateless .NET components, and more. And, you end up spending a lot of time in details that you really don’t need to. On the other hand, if you generate code from an O/R mapping tool, you get well design objects and you only need to deal with their public interface.
Below is an example of code you’ll write if you used an O/R mapping tool.

try { 
    Employees objInfo = new Employees();    
EmployeesFactory objFactory = new EmployeesFactory();
      objInfo.EmployeeID = EmployeeID;     
objFactory.Load(objInfo); 
    // code here to use the “objInfo” object  
}   
catch(Exception ex) { 
    // code here to handle the exception     
return;      
}

As you can see, the generated code is very simple to use than actually writing the .NET components yourself.
Many people have never heard of O/R mapping tools and many more have heard of them but are afraid to use them. I hope I have made a strong enough case here for you to give a serious consideration to O/R mapping for your project.
Iqbal Khan is the Director Sales & Marketing at AlachiSoft (http://www.alachisoft.com), a leading provider of O/R Mapping tool called TierDeveloper. You can reach him at [email protected].