C# LINQ XML Query

问题

I am brand new to working with LINQ. For whatever reason, I am having a very hard time digesting it. The XML document I have seems to be pretty simple, but I am not finding any pages that are helping me.

I need to extract the AttributeValue field from each. (Not as a for each, but discreetly and store in a dedicated var for each AttributeId.)

This is the XML:

    <?xml version="1.0" encoding="UTF-8"?>
    <Request xmlns="urn:oasis:names:tc:xacml:2.0:context:schema:os">
        <Subject SubjectCategory="urn:oasis:names:tc:xacml:1.0:subject-category:access-subject">
            <Attribute AttributeId="urn:oasis:names:tc:xacml:1.0:subject:role-id" DataType="http://www.w3.org/2001/XMLSchema#string" Issuer="requestor">
                <AttributeValue>CISCO:UC:UCMPolicy</AttributeValue>
            </Attribute>
            <Attribute AttributeId="urn:Cisco:uc:1.0:callingnumber" DataType="http://www.w3.org/2001/XMLSchema#string">
                <AttributeValue>10000</AttributeValue>
            </Attribute>
            <Attribute AttributeId="urn:Cisco:uc:1.0:callednumber" DataType="http://www.w3.org/2001/XMLSchema#string">
                <AttributeValue>94146172510</AttributeValue>
            </Attribute>
            <Attribute AttributeId="urn:Cisco:uc:1.0:transformedcgpn" DataType="http://www.w3.org/2001/XMLSchema#string">
                <AttributeValue>10000</AttributeValue>
            </Attribute>
            <Attribute AttributeId="urn:Cisco:uc:1.0:transformedcdpn" DataType="http://www.w3.org/2001/XMLSchema#string">
                <AttributeValue>888884146172510</AttributeValue>
            </Attribute>
        </Subject>
        <Resource>
            <Attribute AttributeId="urn:oasis:names:tc:xacml:1.0:resource:resource-id" DataType="http://www.w3.org/2001/XMLSchema#anyURI">
                <AttributeValue>CISCO:UC:VoiceOrVideoCall</AttributeValue>
            </Attribute>
        </Resource>
        <Action>
            <Attribute AttributeId="urn:oasis:names:tc:xacml:1.0:action:action-id" DataType="http://www.w3.org/2001/XMLSchema#anyURI">
                <AttributeValue>any</AttributeValue>
            </Attribute>
        </Action>
        <Environment>
            <Attribute AttributeId="urn:Cisco:uc:1.0:triggerpointtype" DataType="http://www.w3.org/2001/XMLSchema#string">
                <AttributeValue>translationpattern</AttributeValue>
            </Attribute>
        </Environment>
    </Request>

What I have managed to try so far is not working:

 var query = from t in root.Descendants("Action") where (string)t.Attribute("Attribute") == "urn:oasis:names:tc:xacml:1.0:action:action-id" select t;

As I am still trying to figure this out, I am sure I am giving all the info needed. Let me know what I am missing.

回答1:

You're looking for an Action element that has a Attribute attribute with the value urn:oasis:names:tc:xacml:1.0:action:action-id. That doesn't sound right, does it?

What you actually want to find is an AttributeValue element that belongs to an Attribute element with the AttributeId attribute with the value urn:oasis:names:tc:xacml:1.0:action:action-id.

You also need to take the namespace into account, which is specified in the root element as urn:oasis:names:tc:xacml:2.0:context:schema:os.

XNamespace ns = "urn:oasis:names:tc:xacml:2.0:context:schema:os";

var id = "urn:oasis:names:tc:xacml:1.0:action:action-id";

var value = (string) doc.Descendants(ns + "Attribute")
    .Where(x => (string)x.Attribute("AttributeId") == id)
    .Elements(ns + "AttributeValue")
    .Single();

See this fiddle for a working demo.

来源：https://stackoverflow.com/questions/38125692/c-sharp-linq-xml-query