使用LINQ C＃在XML中使用XElement的值过滤查询

Question

Using LINQ C#, I am querying a database table. The table has a column which contains XML and I would like to filter the results based on an element's value inside the XML being equal to a predefined string. I am using the following query:

(from data in DataObjects.Items
where data.DataItemTimeUtc < DateTime.UtcNow && 
data.DataItemXml.XDocument
   .Descendants("Items")
   .Descendants("MetaData")
   .Descendants("Device")
   .First().Value == "abc123"
orderby data.DataItemTimeUtc descending
select data).ToArray();

but it is failing with an error:

The expression of type 'System.Collections.Generic.IEnumerable`1[System.Xml.Linq.XElement]' is not a sequence

Answer 1

What about this?

var x = DataObjects.Items
 .Where(data => data.DataItemTimeUtc < DateTime.UtcNow
 && data.DataItemXml.XDocument
  .Elements("Items")
  .Elements("MetaData")
  .Elements("Device")
  .First().Value == "abc123")
 .OrderBy(data => data.DataItemTimeUtc);

I've just tried to remove your syntax errors, changed Descendants to Elements which takes only immediate children. Then I changed it to Method Syntax instead of Expression Syntax to keep things together that belong together. You have to be aware though that the .First() might not result any element and then the .Value will throw a null reference exception.