Help with linq

  • Thread starter Thread starter Julie
  • Start date Start date
J

Julie

I have a situation where I have many methods that have a similar linq
expression. Is there a way to re-write to be more efficient?

int Qty1()
{
return (from each in MyData where each.Item1 == 1 select each).Count();
}

int Qty2()
{
return (from each in MyData where each.Item2 == 1 select each).Count();
}

int Qty3()
{
return (from each in MyData where each.Item3 == 1 select each).Count();
}

etc.


What I'd like is a generic Qty method that takes the 'where' condition:

int Qty(??? condition)
{
return (from each in MyData where condition select each).Count();
}

But I have no idea how to do this.

Thanks!
 
Peter said:
That depends a bit on the exact structure of the code, which you don't
show. But, assuming there's nothing too obstrusive going on, something
like this should work:

int Qty(Func<MyElement, bool> condition)
{
return MyData.Count(condition);
}

Assume MyData implements IEnumerable<MyElement>. In other words, just
replace "MyElement" with whatever type each element of MyData actually is.

Then in whatever code you want to use the method, you could call it like
this:

int result = Qty(x => x.Item1 == 1);

Alternatively, keep the methods named "Qty1", "Qty2", etc. and re-write
them to call Qty():

int Qty1()
{
return Qty(x => x.Item1 == 1);
}

Or, you could go straight to the source, and just call
Enumerable.Count() directly:

int result = MyData.Count(x => x.Item == 1);

If the property you're checking is always compared to "1", as your
example suggests, you can fold the comparison into the helper method
instead of making the caller provide it:

int Qty(Func<MyElement, int> funcGetProperty)
{
return MyData.Count(x => funcGetProperty(x) == 1);
}

Then call as so:

int result = Qty(x => x.Item1);

Mix and match the above variations to suit your needs. :)

Note that in all of the above examples, there's no need to write a LINQ
query. The Enumerable.Count() extension method includes an overload
that provides the same filtering behavior you're using the LINQ query to
do.

Pete
Click to expand...

Ok, thanks Pete, that got me a lot further. I prefer the second
solution using the funcGetProperty, but it I couldn't get it to work for
me. I neglected to mention that my I'm using LINQ to SQL, and when
evaluating funcGetProperty, I get an exception

"System.Object DynamicInvoke(System.Object[])' has no supported
translation to SQL."

In looking further into the exception, the error makes sense when
applied to SQL (to a non-SQL source, the code works fine). Are you
aware of a way to convert it to work w/ SQL?

Also, your first solution works fine w/ LINQ to SQL, so at least I've
cleaned up my code a lot from where I was before.

Thanks!
 
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