Question

I’m writing a linq-to-sql query and I’m loading an ID (a bigint in the database and a long in my code) from a table, something like this:

var SomeQuery = (from x in ...
                 select x.ID).SingleOrDefault();

When I get the result, I use SingleOrDefault in case the return is empty. Does that mean that if the result is empty the SomeQuery variable will be 0 or null?

Thanks.

Answer 1

If you look the documenation for SingleOrDefault

Returns the only element of a sequence, or a default value if the
sequence is empty; this method throws an exception if there is more
than one element in the sequence.

It cleary states that if the sequence is empty it will return the default value which for long and bigint is 0. Why explained below

Documenation for default keyword states

In generic classes and methods, one issue that arises is how to assign
a default value to a parameterized type T when you do not know the
following in advance:

Whether T will be a reference type or a value type.

If T is a value type, whether it will be a numeric value or a struct.

Given a variable t of a parameterized type T, the statement t = null
is only valid if T is a reference type and t = 0 will only work for
numeric value types but not for structs. The solution is to use the
default keyword, which will return null for reference types and zero
for numeric value types.