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c#asp.netlinq
huMpty duMpty
huMpty duMpty

Reputation: 14460

What is the best way to check IQueryable result set is null

I just want to know what is the best way to check if an IQueryable result has no values.

eg. if we have a method like

public static IQueryable<Table> DisplayAll()
{
    var db = new DataContext();
    var list= from data in db.Table select data;
    return list;
}

and then we do something like this

var list = DisplayAll();
if(list != null)
{
     //do something --- in here even if the result set has no values it will
     // go to this line. It just say `enumeration yielded no results`
}

Any possible way to check the result set has content or not??

Thanks

Upvotes: 48

Views: 58915

Answers (3)

Dennis Guthrie
Dennis Guthrie

Reputation: 59

Here is what works for me:

    public IQueryable SomeFunc()
    {
        IQueryable result = Repo.SomeLinqQuery();
        if (result.GetEnumerator().MoveNext() == false)
        {
            throw new Exception("Results empty");
        }
        return result;
    }

Upvotes: -1

OzBob
OzBob

Reputation: 4520

An exception will be thrown if IQueryable yeilds no result. I use:

using System.Data.Entity; //for Async support in EF
var tQ = await _tableRepository.DisplayAll();
try { return await tQ.ToListAsync(); }
catch { return null; }

to trap the exception and return null; or an empty List if you prefer,

catch { return new List<Table>(); }

Upvotes: 4

Jon
Jon

Reputation: 437366

list will never be null with LINQ; it will simply represent an "empty collection" if need be. The way to test is with the Any extension method:

if (list.Any()) {
    // list has at least one item
}

Upvotes: 94

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