Difference Between First() and FirstOrDefault() in LINQ

LINQ Is becoming Important Part For Developers..But For New People who Are New To LINQ IS Difficult To Understand Difference Between Many Similar Syntaxes like First() and FirstOrDefault(),Single() and SingleOrDefault() etc.

Here I am going To Explain Difference Between First(0 and FirstOrDefault().

At The Time Of Interview And using LINQ its necessary To Understand Differences Between First() and FirstORDefault().It IS Commonly Used Syntax While Using LINQ().

Here Is Sample Table.

Member

ID	Name	Year	Address	Income	UserName
1	PQR	2010-2011	C	50000	S123
2	PQR	2012-2013	C	180000	S123
3	XYZ	2013-2014	B	200000	S789
4	ABC	2013-2014	A	350000	S253

A. First()

1. When we Use First() in LINQ in Query Syntax Or Method Syntax, At that Time If we Do not Get any Record Corresponding To Expression in Where Clause then It Will Throw You Exception as: InvalidOperationException: Sequence contains no elements.
   

   Var x=(from m in Member
   Where m.UserName=’S000’
   Select m.Name,m.Income,m.Year ).First()

   In The Member table There Is no Such Record Which Will Match the expression so Above Query will Throw: InvalidOperationException: Sequence contains no elements.
   
   We Can Handle This Exception In C# by using try Catch like:
   

   try
   {
      Var x=(from m in Member
      Where m.UserName=’S000’
      Select m.Name,m.Income,m.Year
      ).First()
   
   }
   catch (InvalidOperationException ex)
   {
      Console.WriteLine(ex.Message);
   }

2. When There Are Multiple Records Releted To TO Matching Expression and If You want only the First One Then You can Use First().
   
   i.e:
   

   Var x=(from m in Member
   Where m.UserName=’s123’
   Select m.Name,m.Income,m.Year).First()

   Then You Will get The Result Like:
   
   

   PQR

   2010-11

   50000

   S123

   
   
3. First() returns First Element Of Sequence.
   
   
4. First() throws Exception when There IS No element Presnt In Table.

B. FirstORDefault():

1. When we Use FirstORDefault () in LINQ in Query Syntax Or Method Syntax, At that Time If we Do not Get any Record Corresponding To Criteria in Where Clause then It Will return Some Default Value (Null).
   

   Var x=(from m in Member
   Where m.UserName=’S000’
   Select m.Name,m.Income,m.Year ).FirstOrDefault()

   In The Member table There Is no Such Record Which Will Match the expression so Above Query will Return Default value as Null but Not An Exception.
   
   But when we use above code in c# then it might throw an Exception like:
   

   Console.WriteLine(x.Name);

   It Will Throw An Exception ( because x has Got Null Value because Of Absence Of Record In Table):
   “object reference not set to an instance of an object”.
   
   We Can Handle This Exception In C# by using try Catch like:
   

   try
   {
      Var x=(from m in Member
      Where m.UserName=’S000’
      Select m.Name,m.Income,m.Year ). FirstOrDefault ()
      If(x!=null)
      {
          Console.WriteLine(x.Name);
      }
      else
      {
        Console.WriteLine("No Record Found");
      }
   }
   catch (Exception ex)
   {
      Console.WriteLine(ex.Message);
   }

2. When There Are Multiple Records Releted To TO Matching Expression and If You want only the First One Then You can Use First().
   
   i.e
   

   Var x=(from m in Member
   Where m.UserName=’S123’
   Select m.Name,m.Income,m.Year ).FirstOrDefault()

   Then You Will get The Result Like:
   
   

   PQR

   2010-11

   50000

   S123

   
   
3. FirstOrDefault () returns First Element Of Sequence.
   
   
4. FirstOrDefault () does not throws Exception when There IS No element Present in Table.