To understand how execution take place consider below code:

//Query not going to execute at this point
var query = from customer in db.Customers  
            where customer.City == "Paris" 
            select customer; 

Most of the people think that the query gets executed at this place but the its not right its get executed when I use query collection for
example

//Query get executed at this point
foreach( customer c in query) 
{
  // your code 
}

Or

int count = (from customer in db.Customers  
            where customer.City == "Paris" 
            select customer).Count();

or to .ToList() or any other function which cause execution.


Consider another scenario

I write code like this

var query = from customer in db.Customers  
            where customer.City == "Paris" 
            select customer;

than change code to below line

query = from customer in db.Customers  
            where customer.City == "Mumbai" 
            select customer; 

and than try to use query object

//it get count of all customer which is related to city Mumbai rather than paris.

int count = query.Count(); 

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