LINQ SingleOrDefault Method

In LINQ, the SingleOrDefault operator is used to return a single element or default value if there are no elements present in the list/collection. In case if the list/collection returns more than one element, it will throw an exception like a Single() method.

Syntax of LINQ SingleOrDefault() Example

Following is the syntax of using the LINQ SingleOrDefault() method to get a single element from the collection.

C# Code

int val = objList.SingleOrDefault();

VB.NET Code

Dim val As Integer = objList.SingleOrDefault()

If you observe the above syntax, it will return a single element from the collection “objList” or if the collection contains no elements, it will return the default value.

Example of LINQ SingleOrDefault Method

Following is the example of the LINQ SingleOrDefault method to get a single element from a collection or a default value if the collection contains no elements.

C# Code

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

 namespace LINQExamples
 {
  class Program
  {
    static void Main(string[] args)
    {
      List<Student> objStudent = new List<Student>()
      {
        new Student() { Name = "Suresh Dasari", Gender = "Male",Location="Chennai" },
        new Student() { Name = "Rohini Alavala", Gender = "Female", Location="Chennai" },
        new Student() { Name = "Praveen Alavala", Gender = "Male",Location="Bangalore" },
        new Student() { Name = "Sateesh Alavala", Gender = "Male", Location ="Vizag"},
        new Student() { Name = "Madhav Sai", Gender = "Male", Location="Nagpur"}
      };
      int[] objList = { 1,2,3,4,5 };
      var user = objStudent.SingleOrDefault(i => i.Name == "Suresh Dasari");
      string result = user.Name;
      int val = objList.SingleOrDefault(j=>j>5);
      Console.WriteLine("Element from objStudent: {0}", result);
      Console.WriteLine("Element from objList: {0}", val);
      Console.ReadLine();
    }
  }
  class Student
  {
    public string Name { get; set; }
    public string Gender { get; set; }
    public string Location { get; set; }
  }
 }

VB.NET Code

Module Module1

 Sub Main()
 Dim objStudent As New List(Of Student)() From {
 New Student() With {.Name = "Suresh Dasari", .Gender = "Male", .Location = "Chennai"},
 New Student() With {.Name = "Rohini Alavala", .Gender = "Female", .Location = "Chennai"},
 New Student() With {.Name = "Praveen Alavala", .Gender = "Male", .Location = "Bangalore"},
 New Student() With {.Name = "Sateesh Alavala", .Gender = "Male", .Location = "Vizag"},
 New Student() With {.Name = "Madhav Sai", .Gender = "Male", .Location = "Nagpur"}
 }
 Dim objList As Integer() = {1, 2, 3, 4, 5}
 Dim user = objStudent.SingleOrDefault(Function(s) s.Name = "Suresh Dasari")
 Dim result As String = user.Name
 Dim val As Integer = objList.SingleOrDefault(Function(i) i > 5)
 Console.WriteLine("Element from objStudent: {0}", result)
 Console.WriteLine("Element from objList: {0}", val)
 Console.ReadLine()
 End Sub
 Class Student
 Public Property Name() As String
 Get
 Return m_Name
 End Get
 Set(ByVal value As String)
 m_Name = value
 End Set
 End Property
 Private m_Name As String
 Public Property Gender() As String
 Get
 Return m_Gender
 End Get
 Set(ByVal value As String)
 m_Gender = value
 End Set
 End Property
 Private m_Gender As String
 Public Property Location() As String
 Get
 Return m_Location
 End Get
 Set(ByVal value As String)
 m_Location = value
 End Set
 End Property
 Private m_Location As String
 End Class
 End Module

If you observe the above example, we are trying to get a single element from two lists (objStudent, objList) objects using the LINQ SingleOrDefault method.

Output of LINQ SingleOrDefault() Method Example

Following is the result of the LINQ SingleOrDefault() method example.

Element from objStudent: Suresh Dasari
 Element from objList: 0

The LINQ SingleOrDefault() method will throw InvalidOperationException error in case if the list / collection returns more than one element.