Select Xml Node using Linq to XML

问题:

my Xml file :

<?xml version="1.0" encoding="utf-8"?>
<ArrayOfCustomer xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"  xmlns:xsd="http://www.w3.org/2001/XMLSchema">
    <Customer>
        <CustomerId>1f323c97-2015-4a3d-9956-a93115c272ea</CustomerId>
        <FirstName>Aria</FirstName>
        <LastName>Stark</LastName>
        <DOB>1999-01-01T00:00:00</DOB>
    </Customer>
    <Customer>
        <CustomerId>c9c326c2-1e27-440b-9b25-c79b1d9c80ed</CustomerId>
        <FirstName>John</FirstName>
        <LastName>Snow</LastName>
        <DOB>1983-01-01T00:00:00</DOB>
    </Customer>
</ArrayOfCustomer>  

my attempt :

XElement toEdit = 
    (XElement)doc.Descendants("ArrayOfCustomer")
                 .Descendants("Customer")
                 .Where(x => Guid.Parse((x.Descendants("CustomerId") as XElement).Value) == customer.CustomerId)
                 .First<XElement>();

this throws the following exception :

 Object reference not set to an instance of an object.

1) isn't x an XElement?

2) is this a proper where lambda for selecting an Xml node?

3) and of course how would you find this node according to CustomerId?

回答1:

Your problem is that Descendents and Where return an IEnumerable<XElement> not a single XElement which is what you're after. You can fix this like this:

XElement toEdit = doc.Descendants("ArrayOfCustomer")
                     .Descendants("Customer")
                     .Where(x => Guid.Parse(x.Descendants("CustomerId").Single().Value) == customer.CustomerId)
                     .FirstOrDefault();

回答2:

You are not casting x you are casting x.Descendants(). x.Descendants() returns a collection, hence the plural method semantic. Off the top of my head you should be able to do x.Descendants("CustomerId").FirstOrDefault() as XElement

回答3:

XElement toEdit = (from c in doc.Descendants("Customer")
     where Guid.Parse(c.Value) == customer.CustomerId
     select c).SingleOrDefault();

回答4:

I would restructure your query like this:

 XElement toEdit = doc.Descendants("Customer")
                      .Where(x => (Guid)x.Element("CustomerId") == customer.CustomerId)
                      .FirstOrDefault();