In LINQ, SingleOrDefault operator is used to return a single element or default value in case if there are no elements present in the list / collection. In case if the list/collection returns more than one element then it will throw an exception like a Single() method.
Following is the syntax of using LINQ SingleOrDefault() method to get single element from the collection.
C# Code
int val = objList.SingleOrDefault();
VB.NET Code
Dim val As Integer = objList.SingleOrDefault()
If you observe above syntax it will return single element from the collection “objList” or in case, if the collection contains no elements then it will return the default value.
Following is the example of LINQ SingleOrDefault method to get single element from collection or default value in case if 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 above example we are trying to get single element from two list (objStudent, objList) objects by using LINQ SingleOrDefault method.
Following is the result of 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.
Following is the example which will throw an exception because collection will return more than one element.
C# Code
int[] objList = { 1,2,3,4,5 };
int val = objList.SingleOrDefault();
Console.WriteLine("Element from objList: {0}", val);
Console.ReadLine();
VB.NET Code
Dim objList As Integer() = {1, 2, 3, 4, 5}
Dim val As Integer = objList.SingleOrDefault()
Console.WriteLine("Element from objList: {0}", val)
Console.ReadLine()
If we run above example it will throw InvalidOperationException error because objList returns more than one value.