IEnumerable & IQueryable

Hi,

pls refer this url

http://stackoverflow.com/questions/252785/what-is-the-difference-between-iqueryablet-and-ienumerablet/252857#252857



thanks.


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To return a collection we use IQueryable.But it differs in many ways from other return types.
Using IQueryable , you can save a lot of resources.
It is used for filtering the records in extension methods.
When we use:
 public static IQueryable GetEmployeeDetails()

  {

  return Employees.Where(e => e.Salary >= 10000);

  }
When the method is executed,the SQL executed will be "Select * from Employee where Salary>=10000".
It returns only those records in to the collection  which satisfy the condition.
but when we use IEnumerable ,the SQL executed will be "Select * from Employee" and returns every record.

IQueryable extends IEnumerable, and also stores the Expressions (not just Funcs).  Whereas a Func is a delegate and an Expression is, well, an expression that is able to be traversed at runtime.  And that means it can be translated into SQL.
The .Where extension method for an IEnumerable takes a Func whereas the .Where extension method for an IQueryable takes an Expression>.

What this means is that if we change our filter extension method to take an IEnumerable, it will be using the IEnumerable's .Where extension method, passing in a compiled delegate instead of a traversable expression (they both can be inferred from the same code, in the above case e => e.Salary >= 10000, how it gets compiled depends on which method you call).

For more information on Linq follow the link below:new link

LINQ supports two types of query - local queries for local object collections and interpreted queries for remote data sources.

Local queries operate over collections which implement IEnumerable and use the query operators in the Enumerable static class. These emit normal IL at compile time.

Interpreted queries operate over collections which implement IQueryable and use the query operators in the Queryable static class. These emit 'expression trees' that are interpreted at runtime - hence the name.

It is also possible to query non-generic collections which implement IEnumerable (for local queries) or IQueryable (for interpreted queries) by casting to a specific type.