LINQ to XML - Trying to select a list of elements by the value of their attributes

Question

I'm trying to get a list of elements out of an XML document where the nodes have a specific attribute value. The document is structured something like this:

<root>
  <node type="type1">some text</node>
  <node type="type2">some other text</node>
  <node type="type1">some more text</node>
  <node type="type2">even more text</node>
</root>

The result I'd like to have is an IEnumerable<XElement> containing the two node with type="type1" eg

  <node type="type1">some text</node>
  <node type="type1">some more text</node>

I'm loading the document using var doc = XDocument.Load(@"C:\\document.xml");

I can get an IEnumerable<XAttribute> containing the attributes from the nodes I want using

var foo = doc.Descendants("node")
    .Attributes("type")
    .Where(x => x.Value == "type1")
    .ToList();

However, if I try to get the elements that contain those attributes using the code below I get an Object reference not set to an instance of an object. error. The code I used is

var bar = doc.Descendants("node")
    .Where(x => x.Attribute("type").Value == "type1")
    .ToList();

Any help on figuring out why I'm not getting the results I expect would be appreciated.

Answer 1

That may happen if a node lacks the attribute. Try:

 var bar = doc.Descendants("node")
    .Where(x => (string)x.Attribute("type") == "type1")
    .ToList();

Answer 2

var bar = doc.Descendants("node")
.Where(x => x.Attribute("type") != null && x.Attribute("type").Value == "type1")
.ToList();

Adding a guard for null values solves your problem.

Answer 3

var bar = doc.Descendants() //Checking all the nodes, not just the "node"
.Where(x => x.Attribute("type")?.Value == "type1")//if the attribute "type" is not null, check the Value == "type1",  
.ToList();//immediately executes the query and returns a List<XElement> by the value of attribute "type"

this is an option, if you need to check the value of a specific attribute in all nodes of a document / element.