IQueryable vs IEnumerable

Introduction

 

Hi folks, recently we have covered IEnumerable vs IEnumerator.

 

Today let's try to understand why we have Iqueryable in C# when IEnumerable can get the work done.

 

Say we have DB mapped into our project, If you want to learn how to do that, then you can visit dbfirst-approach step by step guide.

 

First, let's understand what IQueryable is:

• Iqueryable is an interface used to iterate through collections.
  
• It inherits the IEnumerable interface & can be found in System.Linq namespace.

 

There is a key difference between IQueryable & IEnumerable,

 

IEnumerable fetches all the data from SQLServer then it applies filters over fetched data. Let's break-down its flow from the client to the server.

• The client makes a call to fetch data with filters using Entity Framework with IEnumerable
• SQL Server receives a request, It returns all the data without applying any specified filters
• The client receives a response, then it applies filters on client-side.

 

The result of this is that it consumes more time as it transfers all the data without filtering through a network.

 

Where IQueryable fetches filtered records from SQLServer rather than fetching all the records altogether. Let's break-down its flow from the client to the server.

• The client makes a call to fetch data with filters using Entity Framework with IQueryable
• SQL Server receives a request, It returns all the data after applying all the specified filter
• The client receives a response as expected. Now the client won't worry about filtering the records as they are already been filtered.

It consumes less time, as it transfers only filtered records through a network. 

 

Let's see this in action.

 

Let's check what do we have in the database

 

8 records, we will filter these records based on salary. Fetch records with a salary greater than 45000

 

To understand the time consumed by both IEnumerable & IQueryable let's print the time taken by both

 

 

1st IEnumerable:

using (var db = new EmployeeDBEntities())
          {
              DateTime now = DateTime.Now;

              IEnumerable<Employee> employees= from emp in db.Employees
                                              where emp.Salary > 45000
                                              orderby emp.Salary
                                              select emp;
              Console.WriteLine("Time taken by IEnumerable:" + (DateTime.Now - now).Milliseconds + " Milliseconds");
              Console.WriteLine("Employess with salaries > 45000");
              foreach (var item in employees)
              {
                  Console.WriteLine("Name: "+item.FirstName + ",     Salary: " + item.Salary);
              }
           }

Output

 

Time taken by IEnumerable is 634 milliseconds.

 

 

Now let's filter data with IQueryable.

using (var db = new EmployeeDBEntities())
{
    DateTime now = DateTime.Now;

    IQueryable<Employee> employees= from emp in db.Employees
                                    where emp.Salary > 45000
                                    orderby emp.Salary
                                    select emp;
    Console.WriteLine("Time taken by IQueryable:" + (DateTime.Now - now).Milliseconds + " Milliseconds");
    Console.WriteLine("Employess with salaries > 45000");
    foreach (var item in employees)
    {
        Console.WriteLine("Name: "+item.FirstName + ",     Salary: " + item.Salary);
    }
 }

Output

 

Time taken by IQueryable is 325 milliseconds, almost half of IEnumerable.

 

 

Note

The difference between this time depends on a lot of factors.

• How fast is your network bandwidth?
• How many filters have been applied?
• How many records are transferring through the network?

Conclusion

 

In this article, we learned:

• What is IQuerable & how to use?
• Where to use IQueryable.
• What is the difference between Iqueryable & IEnumerable?

Thanks a lot. I hope this article was helpful to all of you.

 

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