Linq with safe cast and null verification

Question

Given the code:

from i in this.GridViewFoo.SelectedItems
select new EmployeeEntity
{
    EmployeeID = (i as EmployeeDto).EmployeeID,
    Email = this.GetAllEmail((i as EmployeeDto).Email, (i as EmployeeDto).SecondaryEmails),
    EmployeeNumber = (i as EmployeeDto).EmployeeNumber,
    FirstName = (i as EmployeeDto).FirstName,
    LastName = (i as EmployeeDto).LastName
}

After the safe cast (i as EmployeeDto) may I receive a NullReferenceException. How can I ensure and safety of the code and not overload him with a lot of null checks?

Overview of solutions:

I did some tests to assert if the solutions are working. Both are working well and bring the same result, you can check HERE. After that I did some performance tests with OfTypeSolution and letSolution.

As OfType solution have better times in average, this will be the answer!

Possible duplicate of [When to use Cast() and Oftype() in Linq](http://stackoverflow.com/questions/4015930/when-to-use-cast-and-oftype-in-linq) — Michael Freidgeim, Aug 25 '16 at 08:05

score 11 · Accepted Answer · answered Sep 19 '12 at 15:22

11

You can use OfType before the Select:

from i in this.GridViewFoo.SelectedItems.OfType<EmployeeDto>()
select new EmployeeEntity
{
    EmployeeID = i.EmployeeID,
    Email = this.GetAllEmail(i.Email, i.SecondaryEmails),
    EmployeeNumber = i.EmployeeNumber,
    FirstName = i.FirstName,
    LastName = i.LastName
}

it will provide you only with the EmployeeDto type items from the SelectedItems so there is no need to cast and null checking.

answered Sep 19 '12 at 15:22

nemesv

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This avoids having numerous empty entries in the output, too. – Dan Puzey Sep 19 '12 at 15:24

score 2 · Answer 2 · answered Sep 19 '12 at 15:27

from si in this.GridViewFoo.SelectedItems
let i = si as EmployeeDto
where i != null
select new EmployeeEntity
{
    EmployeeID = i.EmployeeID,
    Email = this.GetAllEmail(i.Email, i.SecondaryEmails),
    EmployeeNumber = i.EmployeeNumber,
    FirstName = i.FirstName,
    LastName = i.LastName
}

Linq with safe cast and null verification

2 Answers2