C# LINQ : SingleOrDefault() Vs. FirstOrDefault()

LINQ provides the operators like Single (), SingleOrDefault(), First() and FirstOrDefault(), they select a specific record from collection.SingleOrDefault() and FirstDefault() returns NULL or Default Value if there is no matching record found.

here is a list of customers :

 List<Customer>Customers = new List<Customer>

            {

                 new Customer { CustomerID = 1, Name= “Herry” },

                 new Customer { CustomerID = 2, Name=”Tom” }

            };

Select record by using FirstOrDefault() method

  Customer customer = Customers.FirstOrDefault(x => x.CustomerID = 1)

Select record by using SingleOrDefault() method

                Customer customer = Customers.SingleOrDefault(x => x.CustomerID = 2);

SingleOrDefault() vs FirstOrDefault()

• SingleOrDefault() throw exception if we have more than one matching records, and FirstOrDefault() returns the first matching record in sequence.
• Both SingleOrDefault() and  FirstOrDefault() return default value or NULL, If no matching record found.
• FirstOrDefault() generates the TSQL statement "SELECT TOP 1..." and SelectOrDefault() generates regular TSQL statement "SELECT ..”
• In Performance, FirstOrDefault() is usually faster than SingleOrDefault(). The FirstOrDefault() doesn’t care about record uniqueness and amount of record

Recommendations: if you sure, the query should result in at most a single result, you should use SingleOrDefault(), and on other side if query return any number of results, you should use FirstOrDefault() method.

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