Entity Framework Tutorial 1 - Single | SingleOrDefault | First | FirstOrDefault

                       

EF Core Method Comparison

Method	Description	Throws Exception	Returns Null	Use Case
Single	Returns the only element of a sequence, and throws an exception if there is not exactly one element.	If no elements or more than one element are found.	Never	When exactly one element is expected in the result set, and any deviation is an error condition.
SingleOrDefault	Returns the only element of a sequence, or a default value if the sequence is empty. Throws an exception if there is more than one element.	If more than one element is found.	If no elements are found.	When zero or one element is expected. More than one element is considered an error condition.
First	Returns the first element of a sequence. Throws an exception if no elements are found.	If no elements are found.	Never	When at least one element is expected, and only the first element is needed.
FirstOrDefault	Returns the first element of a sequence, or a default value if the sequence is empty.	Never	If no elements are found.	When zero or more elements are expected, and only the first element is needed.

Examples:

Single:

var item = dbContext.Items.Single(i => i.Id == 1);
// Throws InvalidOperationException if no item or more than one item with Id == 1.
        

SingleOrDefault:

var item = dbContext.Items.SingleOrDefault(i => i.Id == 1);
// Throws InvalidOperationException if more than one item with Id == 1.
// Returns null if no item with Id == 1.
        

First:

var item = dbContext.Items.First(i => i.Id == 1);
// Throws InvalidOperationException if no item with Id == 1.
        

FirstOrDefault:

var item = dbContext.Items.FirstOrDefault(i => i.Id == 1);
// Returns null if no item with Id == 1.