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check for empty results from linq to data entites query

Answer 1

A:

you can use Count

IEnumerable<string> xrefLineItems = from xref in db.wysLkupItemCrossRefs
                                    where xref.EndPointCustID == inCustID
                                    select xref.BuyersItemNo;  

if (xrefLineItems.Count() == 0)
{
  // empty
}

fampinheiro 2010-08-31 21:21:56

I tried that in the very beginning and recieved the NotSupported exception about The method 'First' can only be used as a final query operation. Consider using the method 'FirstOrDefault' in this instance instead. Evidently the Count() method calls first just like the .Any() method seems to.

Bob Cummings 2010-08-31 21:24:23

No. [Don't use Count when you mean Any.](http://blogs.teamb.com/craigstuntz/2010/04/21/38598/) Neither `Count` nor `Any` call `First`. His question is misleading.

Craig Stuntz 2010-09-01 12:46:31

Answer 2

A:

Any() is the correct method.

Neither Any() nor Count() call First(). If you are seeing this, then your bug is elsewhere. Look at the call stack for the exception.

Craig Stuntz 2010-09-01 12:48:24

OK I posted the stack trace. I am not the best at reading them, so if you can show me where the bug is generated, I would appreciate it very much.

Bob Cummings 2010-09-01 14:56:19

All that stack says is that you have a `First()` in some query you're not showing us. The EF is trying to translate it to SQL, but it's not used correctly. The error is in code which is not in your post.

Craig Stuntz 2010-09-01 15:22:20

Thanks, the only code is being show, where the query is done (first code section) then when I try to check to see if there were any results returned. I just wrote a stored procedure and call that instead of trying to build the query (shown in the first code section) and then the .ALL works.thanks again for your effortbob

Bob Cummings 2010-09-01 20:32:39

I know that's the only code you *see*, but with lazy evaluation it's likely not the only code which *runs.*

Craig Stuntz 2010-09-01 20:47:53

Thanks for tip about lazy evaluation. Any hints on where I can learn more about this concept? Otherwise I can just Google it, and work it out myself. I feel as if I am "Programming by Coincidence". And need to get beyond that, and fully understand what is going on, for my own piece of mind and to be able to ask better questions and understand the answers. thanks again for everything.cheersbob

Bob Cummings 2010-09-02 13:03:04

You could do worse than Googling LINQ + lazy. But the basic idea is that no query is executed or even translated to SQL until it *has to* be evaluated. `.Any()` forces translation to SQL. Errors elsewhere in the code won't surface until that point. Search your code for `First()`; it should never appear *inside* an L2E query; you can only apply it to the whole query itself.

Craig Stuntz 2010-09-02 13:11:30

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