How can I use the conditional null operator to check for null string?

Question

I'm trying to execute the LINQ to objects query as follows:

var c1 = allCustomers
    .Where(x => x.CompanyName.Replace("'", "").StartsWith(searchText))
    .ToList();

This works fine as long as CompanyName is not null.

So, I thought this seems like the perfect place for the new null conditional operator! Just change to:

var c1 = allCustomers
    .Where(x => x.CompanyName?.Replace("'", "").StartsWith(searchText))
    .ToList();

and everything should work!

Instead, I get the error:

Cannot implicitly convert type 'bool?' to 'bool'. An explicit conversion exists (are you missing a cast?)

I'm not quite sure how to accomplish what I want here. How would I use the null conditional in this scenario?

Jeffrey Hantin · Accepted Answer · 2016-04-22 23:52:18Z

5

You need a coalesce operator to convert the tri-state to a proper boolean.

var c1 = allCustomers
    .Where(x => x.CompanyName?.Replace("'", "").StartsWith(searchText) ?? false)
    .ToList();

I call bool? a tri-state because it can have three values: true, false and null; therefore, converting bool? to bool is a narrowing conversion that requires explicit treatment.

answered Apr 22, 2016 at 23:52

Jeffrey Hantin

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Comments

John Gardner · Accepted Answer · 2016-04-22 23:52:10Z

1

you need more question marks! i think you need null coalescing as well, since x.CompanyName?.Replace could now also return null.

(x.CompanyName?.Replace("'", "") ?? string.Empty).StartsWith(searchText))

the ?? string.empty forces that to be a non-null string, which now supports .startswith

answered Apr 22, 2016 at 23:52

John Gardner

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3 Comments

John Gardner Over a year ago

ack, i put mine on the string instead of the bool. i think mine will work, but the ?? false versions are better.

Scottie Over a year ago

Yeah, the other 2 will short circuit on the .? and simply return false.

John Gardner Over a year ago

i interpreted the question tool literally on the "check for null string" part, not on the `bool?' part in the details.

Tomasz Sołtysik · Accepted Answer · 2016-04-22 23:52:52Z

1

Use ?? operator like:

Where(x => x.CompanyName?.Replace("'", "").StartsWith(searchText) ?? false)

answered Apr 22, 2016 at 23:52

Tomasz Sołtysik

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1 Comment

Lukazoid Over a year ago

Could you provide some explanation of why the null-coalescing operator would solve this?

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