10 Things You Should Know About LINQ

10 fundamental things that you should know about LINQ

1. LINQ is Language INtegrated Query where the queries to data sources are written as part of the High Level .NET programming Language (like C# or VB.NET).

2. The queries, which are the language constructs, can be compiled using the language compilers. This ensures type-safety. The queries can also be debugged using the Visual Studio debugger (an awesome feature, I believe)

3. Intellisense can be used to access tables and their columns of a database. This feature is not present in the CTP versions but would be delivered with the Orcas release.

4. LINQ provides Standard Query Operators (SQOs) (like select, union, where etc) to retrieve data from any object whose class implements the IEnumerable interface. This is called "LINQ to Objects". The object, or rather data source, can be virtually anything: a registry collection or a File collection or a database.

5. LINQ also provides SQOs to work with relational data, also called as "LINQ to ADO.NET or DLINK". It is comprised of three parts: “LINQ to SQL”; to query relational databases like SQL Server, “LINQ to DataSet”; supports queries using ADO.NET datasets and datatables and “LINQ to Entities”; to query ADO.NET 3.0 entities (Entities are part of Entity Framework of ADO.NET 3.0)

6. LINQ provides SQOs for XML documents, called "LINQ to XML or XLINK". It also provides a host of new XML-specific features for XML document creation and queries. It can be considered as a powerful replacement for DOM and XPath.

7. WebLINQ, also known as BLINQ, creates CRUD ASP.NET pages (infact, a complete website) against a database using LINQ. It also preserves relationships between tables by providing an option on the aspx pages to view the related records from the related tables. I would suggest you to check this wonderful feature.

8. LINQ not just supports simple queries but also stored procedures.

9. LINQ can be used to query on a join of different datasources. For example an RSS feed of a Blog, a collection object (like registry) and a bunch of rows from a database can all be joined together (using a SQO) and then be queried on.

10. LINQ maintains object identity. In other words, if two queries return the same information (say form a table), only one instance of that table “as an object” is maintained. This makes sure that objects are not created unnecessarily. This is a classic issue in ORM models, which is eliminated here.

With every release of a framework, life for developers is being made easier. With LINQ, so much code has been made simple to write and manage, that it cannot be put in less than a bible. I wonder if someday I would be jobless!

Three cheers to LINQ!

(Reproduced from my Infosys Blog)

Every Type is derived from...

A simple question...

Which is the type from which every other type is derived? Think before you look forward!
If you are answer is System.Object, then it's partially correct. The actual answer is System.Object if it's a reference type. If it is a value type then it derives from System.ValueType.

Multiple Entry Points

A dot net program has a single point of entry (which is generally the Main function).
public static void Main(int args[])

A well-known fact:The execution of the program starts from here. If we look at the sig of the function we see that the Main function is publi. But ever wondered what happens if the sig is: private static void Main(int args[])?

The Main method is invoked from outside of the program. So it is, obviously, essential that the method be public. But would the program compile if it was private? The answer is: YES. It would compile. For some reason, not so obvious to me, the compiler/runtime doesn't see difference between a public and a private Main method. All it needs is a Main method.

So what if, in a program, we have two Main methods, either private or public or both? The compiler/runtime is confused. It doesn't know which is the actual point of entry. So, ambiguity! Hence, errors!

But what if for some reason you want to have two main methods? Can you make things work or is it the end of the road? It's definitely not the end. You can still make it work, with as many Main methods you want. Only condition being, the fully qualified name of the method (or the type containing it) should be different from each of the other Main methods.
namespace MainNamespace
{
class FirstMain
{
public static void Main(int args[]) {}
}

class SecondMain
{
public static void Main(int args[]) {}
}
}

To build this program use:
csc.exe Program.cs /main:MainNamespace.FirstMain

This will do the trick for you.
The next obvious question is how would we compile it using VS 2005? I would take this in my next post.

An Obvious Mistake

class MyClass
{
private void Sample()
{
int i=10;
int i=20;
}
}

Will this code compile?
Obviously it wouldn't!!

But why wouldn't it compile?
Obviously because i has multiple declarations!!

But what is not so obvious is the reason behind not allowing multiple declarations. To talk about those not so obvious reasons, first of all one basic point. What happens when you say int i=10?

4 bytes of memory gets allocated, 10 is stored in it and the identifier 'i' points to it. Simple!

Now let's say we do multiple declarations for i, like in the above program. int i=10 allocates 4 bytes of memory and i points to it. Then we have int i=20. Another 4 bytes is allocated, 20 stored in it and, again, identifier 'i' points to this new memory. So when you use 'i' again anywhere, the compiler or runtime doesn't know which chunk of memory you are trying to reference to! Hence, undesired results!

This is the not so obvious reason for the program not compiling!