In Deferred Execution, the query is not executed when declared. It is executed when the query object is iterated over a loop.

In Immediate Execution, the query is executed when it is declared.

Deferred Execution:

Now we will see both the executions using an example. For this I created a Visual Studio Solution. Here in the solution I added a new Class Employee as in the following screenshot:

Employee
Figure 1: Class Employee

Code

  1. using System;
  2. using System.Collections.Generic;
  3. using System.Linq;
  4. using System.Web;
  6. namespace DeferredVsImmediate_Query
  7. {
  8. public class Employee
  9. {
  10. public int Emp_ID { get; set; }
  11. public string Name { get; set; }
  12. public string Email { get; set; }
  13. public string Country { get; set; }
  14. }
  15. }
Add a New Web Page Default.aspx and add the following code:
  1. using System;
  2. using System.Collections.Generic;
  3. using System.Linq;
  4. using System.Web;
  5. using System.Web.UI;
  6. using System.Web.UI.WebControls;
  8. namespace DeferredVsImmediate_Query
  9. {
  10. public partial class Default : System.Web.UI.Page
  11. {
  12. protected void Page_Load(object sender, EventArgs e)
  13. {
  14. var Emp_List = new List<Employee>(
  15. new Employee[]
  16. {
  17. new Employee{Emp_ID=1, Name="Shambhu Sharma", Email="[email protected]", Country="India"},
  18. new Employee{Emp_ID=2, Name="Manu Khanna", Email="[email protected]", Country="India"},
  19. new Employee{Emp_ID=3, Name="Abhishek Nigam", Email="[email protected]", Country="USA"},
  20. new Employee{Emp_ID=4, Name="Yogesh Gupta", Email="[email protected]", Country="USA"},
  21. new Employee{Emp_ID=5, Name="Shweta Kashyap", Email="[email protected]", Country="India"},
  22. new Employee{Emp_ID=6, Name="Shraddha Gaur", Email="[email protected]", Country="India"},
  23. new Employee{Emp_ID=7, Name="Akhilesh Atwal", Email="[email protected]", Country="India"},
  24. new Employee{Emp_ID=6, Name="Mayank Dhulekar", Email="[email protected]", Country="USA"},
  25. new Employee{Emp_ID=7, Name="Saurabh Mehrotra", Email="[email protected]", Country="USA"},
  26. new Employee{Emp_ID=7, Name="Mehak Jain", Email="[email protected]", Country="India"},
  27. });
  29. var Result = from a in Emp_List
  30. where a.Country.Equals("India")
  31. select new { a.Name };
  33. foreach (var EMP in Result)
  34. Response.Write(EMP.Name + "</br>");
  35. }
  36. }
  37. }
Now run your application:

Now Run
Figure 2: Output

Now you can see the following when your query executes:

see when my query executed
Figure 3: Query Execution

Now add a new record after your query to see the deferred execution:

Add a new record after your query
Figure 4: Deferred Execution

Now run your app:

Now run your app
Figure 5: Output

Immediate Execution: We can force our query to execute immediately as in the following:

query to execute
Figure 6: Immediate Execution

Now run your application:

run your application
Figure 7: Output

Now let us see both the executions:

code
Figure 8: Both the executions