Dealing with NULL collection in Linq query

[Deckarep]

Hey everyone,

Is there a more elegant or cleaner way of accomplishing the following
null check?


List<stringmySt ring = null; //Purposely null list of strings to
show the example

XElement element = new XElement("Strin gs",
(myString != null) ?
(from string s in myString
where s.StartsWith("S ")
select s) : null
);

This XElement yields the following result: <Strings/and empty
Element.


I like that I can write linq to xml in nested declarations like this.
What I don't like now...is doing the null
check with the tertiary starts making the code ugly and less
readable. I know how to handle null values
when some of the contents in the collection may be null but what if
your collection is null itself??

If there's a better more Linq integrated way of handling this that
would be great.

Thanks,

[Jeroen Mostert]

Re: Dealing with NULL collection in Linq query

Deckarep wrote:

Is there a more elegant or cleaner way of accomplishing the following
null check?
>
>
List<stringmySt ring = null; //Purposely null list of strings to
show the example
>
XElement element = new XElement("Strin gs",
(myString != null) ?
(from string s in myString
where s.StartsWith("S ")
select s) : null
);
>
This XElement yields the following result: <Strings/and empty
Element.
>
>
I like that I can write linq to xml in nested declarations like this.
What I don't like now...is doing the null
check with the tertiary starts making the code ugly and less
readable. I know how to handle null values
when some of the contents in the collection may be null but what if
your collection is null itself??
>
If there's a better more Linq integrated way of handling this that
would be great.
>

Don't use null references for collections, use empty collections instead:

List<stringmySt ring = new List<string>();

Edge case disappears. Also, a lambda is clearer here:

XElement element = new XElement(
"Strings",
myString.Where( s =s.StartsWith(" S"))
);

--
J.

http://symbolsprose.blogspot.com

[Gilles Kohl [MVP]]

Re: Dealing with NULL collection in Linq query

On Thu, 15 May 2008 10:44:57 -0700 (PDT), Deckarep
<deckarep@gmail .comwrote:

>
>Hey everyone,
>
>Is there a more elegant or cleaner way of accomplishing the following
>null check?
>
>
>List<stringmyS tring = null; //Purposely null list of strings to
>show the example
>
>XElement element = new XElement("Strin gs",
(myString != null) ?
(from string s in myString
where s.StartsWith("S ")
select s) : null
);
>
>This XElement yields the following result: <Strings/and empty
>Element.
>
>
>I like that I can write linq to xml in nested declarations like this.
>What I don't like now...is doing the null
>check with the tertiary starts making the code ugly and less
>readable. I know how to handle null values
>when some of the contents in the collection may be null but what if
>your collection is null itself??
>
>If there's a better more Linq integrated way of handling this that
>would be great.

Hmm, do you need to be able to differentiate between a null myString
and an empty list of strings?

That is, could you use List<stringmySt ring = new List<string>();
and get rid of the tertiary?

Alternatively, something along these lines:

XElement element = new XElement("Strin gs",
(myString ?? new List<string>()) .Where(s =s.StartsWith(" S")));

Neither strike me as a lot cleaner or more elegant though :-)

Regards,
Gilles.

[Deckarep]

Re: Dealing with NULL collection in Linq query

Good point. I would use an empty collection if I could get away with
it. Unfortunately I'm using a system
that was not designed in this fashion so I often have to check for
null before knowing
if a collection is empty or not. :(

Thanks for the response tip on Lambda!

[Jeroen Mostert]

Re: Dealing with NULL collection in Linq query

Deckarep wrote:

Good point. I would use an empty collection if I could get away with
it. Unfortunately I'm using a system
that was not designed in this fashion so I often have to check for
null before knowing
if a collection is empty or not. :(
>

If you really need to do this a lot, you can cheat your way around it:

public static class EnumerableExten sions {
public static IEnumerable<TEm ptyIfNull<T>(th is IEnumerable<T>
source) {
return source ?? Enumerable.Empt y<T>();
}
}

Now

List<stringstri ngs = null;
strings.EmptyIf Null().Where(s =s.StartsWith(" S"));

will work.

Disclaimer: while neat, I have no idea if this is inefficient compared to
null checks and if so, exactly how much. Also, calling a method on a
reference that's notionally null is obviously a little counterintuitiv e, so
many people would just call this another abuse of extension methods. :-)

--
J.

http://symbolsprose.blogspot.com