C# – getting a “Sequence contains no matching element” error when using .Any

clinqsql

I have a .Any() Linq Method:

db.MyTable.Any(x => x.Year == MyObj.Year && x.Quarter == MyObj.Quarter && x.Week == MyObj.Week)

That is returning the error:

 System.InvalidOperationException occurred
  HResult=0x80131509
  Message=Sequence contains no matching element
  Source=EntityFramework

However the MSDN documentation states that the .Any method returns "true if the source sequence contains any elements; otherwise, false."

Why is this method throwing the exception instead of returning False?

Best Answer

With this little code it is fairly difficult to see what the cause is. It certainly is not in this part of the code.

Try to do some debugging, use the debugger to check all values, or write some Debugging statements before you perform your function:

// Check myObj
MyObjectType myObj = ...         // instead of var, so you are certain you have the right type
Debug.Assert(myObj != null);

// only if Year, Quarter, Week are classes:
Debug.Assert(myObj.Year != null);   
Debug.Assert(myObj.Quarter != null);
Debug.Assert(myObj.Week != null);

// check your db:
Debug.Assert(db != null);
Debug.Assert(db.MyTable != null);
int count1 = db.MyTable.Count();
int count2 = db.MyTable
    .Where(x => x.Year == MyObj.Year 
        && x.Quarter == MyObj.Quarter
        && x.Week == MyObj.Week)
    .Count();
bool hasAny = db.MyTable
    .Where(x => x.Year == MyObj.Year 
        && x.Quarter == MyObj.Quarter
        && x.Week == MyObj.Week)
    .Any();

// if all this works, your statement should also work
hasAny = db.MyTable
    .Any(x => x.Year == MyObj.Year 
        && x.Quarter == MyObj.Quarter
        && x.Week == MyObj.Week);

Related Solutions

.net – LINQ: When to use SingleOrDefault vs. FirstOrDefault() with filtering criteria

If your result set returns 0 records:

SingleOrDefault returns the default value for the type (e.g. default for int is 0)
FirstOrDefault returns the default value for the type

If you result set returns 1 record:

SingleOrDefault returns that record
FirstOrDefault returns that record

If your result set returns many records:

SingleOrDefault throws an exception
FirstOrDefault returns the first record

Conclusion:

If you want an exception to be thrown if the result set contains many records, use SingleOrDefault.

If you always want 1 record no matter what the result set contains, use FirstOrDefault

C# – Sequence contains no matching element

Well, I'd expect it's this line that's throwing the exception:

var documentRow = _dsACL.Documents.First(o => o.ID == id)

First() will throw an exception if it can't find any matching elements. Given that you're testing for null immediately afterwards, it sounds like you want FirstOrDefault(), which returns the default value for the element type (which is null for reference types) if no matching items are found:

var documentRow = _dsACL.Documents.FirstOrDefault(o => o.ID == id)

Other options to consider in some situations are Single() (when you believe there's exactly one matching element) and SingleOrDefault() (when you believe there's exactly one or zero matching elements). I suspect that FirstOrDefault is the best option in this particular case, but it's worth knowing about the others anyway.

On the other hand, it looks like you might actually be better off with a join here in the first place. If you didn't care that it would do all matches (rather than just the first) you could use:

var query = from target in _lstAcl.Documents
            join source in _dsAcl.Document
            where source.ID.ToString() equals target.ID
            select new { source, target };
foreach (var pair in query)
{
    target.Read = source.Read;
    target.ReadRule = source.ReadRule;
    // etc
}

That's simpler and more efficient IMO.

Even if you do decide to keep the loop, I have a couple of suggestions:

Get rid of the outer if. You don't need it, as if Count is zero the for loop body will never execute
Use exclusive upper bounds in for loops - they're more idiomatic in C#:
```
for (i = 0; i < _lstAcl.Documents.Count; i++)
```

Eliminate common subexpressions:

var target = _lstAcl.Documents[i];
// Now use target for the rest of the loop body

Where possible use foreach instead of for to start with:
```
foreach (var target in _lstAcl.Documents)
```

Best Answer

Related Solutions

.net – LINQ: When to use SingleOrDefault vs. FirstOrDefault() with filtering criteria

C# – Sequence contains no matching element

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