Question

Using LINQ to XML, XElements and XAttributes I’d like to filter a query using an exact match on an XElement’s Attributes() IEnumerable collection of XName/Value pairs, against a provided IEnumerable Attributes collection of XName/Value pairs.

<container>
   <!-- logical group of settings -->
   <group name="group-one">
      <!-- setting with multiple key-value key options to return value -->
      <setting>
         <key app="a" command="go" />
         <key app="a" type="z" command="go" />
         <key app="a" type="z" flag="1" command="go" />
         <key app="a" type="z" target="OU812"/>
         <value>group-one item value A</value>
      </setting>
      <setting>
         <key app="a" />
         <key app="a" type="z" />
         <key app="a" type="z" flag="1" />
         <key app="c" type="z" command="go" />
         <value>group-one item value B</value>
      </setting>      
      ...
      ...
   </group>
   <group name="group-two">
      ...
      ...
   </group>
</container>

I suspect using Attributes().SequenceEqual() with a custom IEqualityComparer to compare both XAttribute.XName and XAttribute.Value is the way to go, but the sequence never matches because XElement(“key”).Attributes() returns a collection of all attributes for all elements in a given element. I have tried any number linq queries similar to following code snippet, including nested queries and using the “let” statement, but I can’t seem to get it right.

var myAttributes = new List<XAttribute> {
                                        new XAttribute("app", "a"), 
                                        new XAttribute("type", "z")
                                        };

var xGroup = doc.Elements("group").First(g=>g.Attribute("name").Value==groupName);
var xSetting = (from s in xGroup.Elements("setting")
               // AttributesComparer() compares both the XAttribute.XName and XAttribute.Value properties to determine equality
               where s.Elements("key").Attributes().SequenceEqual(myAttributes, new AttributesComparer())
               select s).FirstOrDefault();

var xValue = xSetting.Element("value");

It should return an XElement representing <value>group-one item value B</value>

For now, I have settled on using XPathSelectElement() — passing an XPath string built from the name/values in the provided XAttributes() collection. In this case, the generated string would be:

group[@name='group-one']/setting[key[@app='n' and @type='z' and count(@*)=2]]/value

But, I’m generally resistant to looping through collections to build strings in an application. I have been hammering away at this for a while now, and unfortunately, I am stumped as to how to impliment a more “elegant” solution using a compact linq query (or series of queries) with existing methods.

Any feedback and/or suggestions would be greatly appreciated!

Answer 1

You need to find a setting where any key matches so use the Any extension method. Only a small change is required:

    var xSetting = (from s in xGroup.Elements("setting")
                    // AttributesComparer() compares both the XAttribute.XName and XAttribute.Value properties to determine equality
                    where s.Elements("key").Any(key => key.Attributes().SequenceEqual(myAttributes, new AttributesComparer()))
                    select s).FirstOrDefault();