IQueryable vs. IEnumerable in terms of LINQ to SQL queries

IQueryable inherited IEnumerable, so it obviously get all the functionality IEnumerable has. The working style of both is still different. There are still lot many differences exists between the two which impact the decision we took in usage of either one. Both of these suits for particular scenarios. Following are some differences using which we can took decision to use anyone of these optimally.

Parameter	IQueryable	IEnumerable
Extension Methods	Extension methods defined for IQueryable take expression objects. Means, the delegate IQueryable extension methods receives is an expression tree.	Extension methods defined for IEnumerable take functional objects. Means, the delegate IEnumerable extension methods receives is a method to invoke.
Great For	IQueryable allows out-of-memory things like remote data source operations, such as working with database or web service.	IEnumerable is great for working with sequences (in-memory collections), that are iterated in-memory.
Supported Queries	IQueryable supports LINQ to SQL queries.	IEnumerable supports LINQ to Object and LINQ to XML queries.
Deferred Execution	IQueryable supports lazy loading (Suited for scenarios like paging and composition based queries).	IEnumerable lost lazy loadnig ability on the external provider.
Moving between items	IQueryable provides many methods to move between the items.	IEnumerable doesn’t have the concept of moving between items, it is forward only collection.
Filtering Mechanism	IQueryable executes query on server side along with all the filters applied.	IEnumerable executes select query on server side, loads data in-memory and then executes filter at client side.
CreateQuery and Execute Methods	IQueryable has these two additional methods. Both takes expression as input. CreateQuery returns IQueryable representing expression tree. Execute returns result of the query.	NA
Custom Querying Capability	IQueryable provides additional functionality to implement custom querying with LINQ.	IEnumerable does not have custom querying capability.
Performance Perspective	IQueryable gives best performance when used for out-of-memory data store operations (that is external to .NET CLR memory).	IEnumerable gives best performance when used to manipulate in-memory collections.

IEnumerable: IEnumerable is best suitable for working with in-memory collection. IEnumerable doesn’t move between items, it is forward only collection.
IQueryable: IQueryable best suits for remote data source, like a database or web service. IQueryable is a very powerful feature that enables a variety of interesting deferred execution scenarios (like paging and composition based queries).


So when you have to simply iterate through the in-memory collection, use IEnumerable, if you need to do any manipulation with the collection like Dataset and other data sources, use IQueryable

Difference between XElement and XDocument

Both are the classes defined by System.Xml.Linq namespace

XElement class
represents an XML fragment
XDocument class represents an entire XML document with all associated meta-data.

example:

XDocument d = new XDocument(
      new XComment("hello"),
      new XElement("book",
              new XElement("bookname", "ASP.NET"),
             new XElement("authorname", "techmedia"),
       )
);

Advantages and disadvantages of LINQ over Stored procedures

Below is the three advantages of LINQ over stored procedures.

Debugging - As debug point concern, as LINQ is part of .NET, we can use the visual studio's debugger to debug the queries but it is tough to debug the Stored procedure as it will not support the visual studio debugger.

Deployment - In case of deployment, we need to provide an additional script for stored procedures to execute but in case of LINQ, it will complie into single DLL hence deployment becomes easier.

Type Safety - As LINQ is type safe, the queries errors are type checked at compile time. Better suggest to use LINQ because it helps to encounter an error at the compile time rather than at runtime exception.

 

 

The disadvantage with LINQ is, it is not a precompiled statement where as stored procedures are precompiled. In case of LINQ the queries need to be compile before the execution. So according to this, I can say stored procedures are faster in performance as compared to LINQ.