Question

I’m having unexpected behavior with the .Contains() function of the where clause in Linq to XML. It seems to be functioning like “==” not Contains() in the string function.

Example:

var q = from sr in SearchResults.Descendants("Result")
    where _filters.Contains((string)sr.Element("itemtype"))
    orderby (string)sr.Element("ipitemtype") ascending
    select new SearchItem
    {
        //Create Object
        ID = (string)sr.Element("blabla"),
    }

_filters is a list of strings. Let’s say it contains 3 values:

_filters[0] = "videos";
_filters[1] = "documents";
_filters[2] = "cat pictures";

What happens now, is that the Query works perfectly if

<itemtype>videos</itemtype> 

is the XML node.

However, if the node is

<itemtype>videos mission critical document advertising</itemtype>, 

the IEnumerable returns blank, which to me says the operand is functioning like “==” not “Contains()”.

Any idea what I’m doing wrong?

Winning answer from dtb:

replace

where _filters.Contains((string)sr.Element("itemtype"))

with

where _filters.Any(filter => ((string)sr.Element("itemtype")).Contains(filter))

Answer 1

Try this:

_filters.Any(s => ((string)sr.Element("itemtype") ?? "").Contains(s))

This way you’re checking that the element’s value contains any of the strings in _filters. The use of the null coalescing operator ensures a NullReferenceException isn’t thrown when the itemtype node doesn’t exist since it is replaced with an empty string.

The other approach is to use let and filter out the nulls:

var q = from sr in SearchResults.Descendants("Result")
        let itemtype = (string)sr.Element("itemtype")
        where itemtype != null &&
              _filters.Any(filter => itemtype.Contains(filter))
        orderby (string)sr.Element("ipitemtype") ascending
        select new SearchItem
        {
            //Create Object
            ID = (string)sr.Element("blabla")
        }

Note that String.Contains is case sensitive. So a check for “videos” won’t match on “Videos” with a capital “V”. To ignore case you can use String.IndexOf in this manner:

_filters.Any(filter => itemtype.IndexOf(filter, StringComparison.InvariantCultureIgnoreCase) >= 0)