AsEnumerable() in C#

The AsEnumerable() method in C# is used to cast a specific type to its IEnumerable<T> equivalent. It is an extension method from the System.Linq namespace that helps when you need to treat a collection as a basic enumerable sequence, often to force LINQ to Objects behavior over LINQ to SQL or Entity Framework queries.

Syntax

Following is the syntax for using AsEnumerable() −

public static IEnumerable<TSource> AsEnumerable<TSource>(this IEnumerable<TSource> source)

Usage example −

var enumerable = collection.AsEnumerable();

Parameters

• source − The sequence to type as IEnumerable<T>.

Return Value

Returns the input sequence typed as IEnumerable<T>.

Using AsEnumerable() with Arrays

The most common use case is converting arrays or other collection types to their IEnumerable equivalent −

using System;
using System.Linq;

class Demo {
    static void Main() {
        int[] arr = new int[5];
        arr[0] = 10;
        arr[1] = 20;
        arr[2] = 30;
        arr[3] = 40;
        arr[4] = 50;
        
        var res = arr.AsEnumerable();
        
        foreach (var ele in res) {
            Console.WriteLine(ele);
        }
    }
}

The output of the above code is −

10
20
30
40
50

Using AsEnumerable() to Force LINQ to Objects

A key benefit of AsEnumerable() is forcing database queries to execute locally instead of on the database server −

using System;
using System.Linq;
using System.Collections.Generic;

class Student {
    public int Id { get; set; }
    public string Name { get; set; }
    public int Score { get; set; }
}

class Program {
    static void Main() {
        var students = new List<Student> {
            new Student { Id = 1, Name = "Alice", Score = 85 },
            new Student { Id = 2, Name = "Bob", Score = 92 },
            new Student { Id = 3, Name = "Carol", Score = 78 }
        };
        
        // Force LINQ to Objects behavior
        var result = students.AsEnumerable()
                           .Where(s => s.Score > 80)
                           .Select(s => s.Name);
        
        foreach (var name in result) {
            Console.WriteLine(name);
        }
    }
}

The output of the above code is −

Alice
Bob

Comparison with Other Conversion Methods

Conclusion

The AsEnumerable() method provides a lightweight way to cast collections to IEnumerable<T> without creating new objects. It is particularly useful for forcing LINQ queries to execute locally instead of being translated to database queries, giving you more control over query execution.