XElement query gives error: "Sequence contains no elements"

Question

I'm trying to query this xml: ``` ``` Here's my function: ``` protected string GetParent(Guid nodeId) { XDocument doc = XDocument.Parse(GetXml()); // parses xml displayed above // returns the 5 page map nodes displayed above IEnumerable nodes = doc.Descendants("pageMapNode"); // error: "Sequence contains no elements" XElement node = doc.Descendants("pageMapNode") .Where(n => n.Attribute("id").ToString().ToLower() == nodeId.ToString().ToLower()).Single(); ... } ``` The nodeId parameter I'm passing in is correct - I should get a match, so I don't know why it's returning an error. Anyone see what I'm doing wrong?

Accepted Answer

`n.Attribute("id")` returns an XAttribute, not a string. You need `.Value` instead of `.ToString()`

```
XElement node = doc.Descendants("pageMapNode")
    .Where(n => n.Attribute("id").Value.ToLower() == 
        nodeId.ToString().ToLower()).Single();
```

and you can shorten it to

```
XElement node = doc.Descendants("pageMapNode")
    .Single(n => n.Attribute("id").Value.ToLower() == 
        nodeId.ToString().ToLower());
```

XElement query gives error: "Sequence contains no elements"

Solution

Problem