如何从其他嵌套元素获取信息？

Question

I am struggling with using LINQ to SQL XML. I'm following examples and getting some good results. However I ran into a problem and hope that someone can help me.

<root>
<MyItem  Host="00155DFF045C" LastName="HOUSTON" FirstName="WHITNEY" >
    <TimeStamp ComputerTime="02/07/2011 - 21:41:53.715">
        <Group Name="Group1">
            <Variable ID="1001" Value="Happy" >
            </Variable>
        </Group>
        <Group Name="Group2">
            <Variable ID="2000" Value="Monday" >
            </Variable>
            <Variable ID="2001" Value="Tuesday" >
            </Variable>
        </Group>
        <Group Name="Group3">
            <Variable ID="3000" Value="January" >
            </Variable>
            <Variable ID="3001" Value="February" >
            </Variable>
        </Group>
        <Group Name="Groupe4">
            <Variable ID="4001" Value="108.000000" >
            </Variable>
            <Variable ID="4002" Value="800" >
            </Variable>
        </Group>
        <Group Name="CustomGroup">
            <Variable ID="1001000" Value="1.000000" >
            </Variable>
        </Group>
    </TimeStamp>
</MyItem>
<MyItem>
...
...
</MyItem>
</root>

I correctly get info like {Host="00155DFF045C" LastName="HOUSTON" FirstName="WHITNEY} thanks to the tutorial.

But I need to get some more information. How can I retrieve Value of the Variable element with ID="4001" which belongs to Groupe4 ?

My current code is:

XElement xmlTweets = XElement.Parse(e.Result);
var toto = from tweet in xmlTweets.Descendants("MyItem").Take(10)
           orderby tweet.Element("TimeStamp").Attribute("ComputerTime").Value descending
           select new History {
               DisplayName = tweet.Attribute("PatientFirstName").Value + " " +
                             tweet.Attribute("PatientLastName").Value
           };

With this code, I can correctly get value for DisplayName . I would like to get value of variable 4001 , ie, value 108.0000 .

Answer 1

If you have a reference to a particular element, you can get values from any of its nested elements using the Element() or Attribute() methods. You can get a list of these using Elements() or Attributes() to perform LINQ queries on them. Assuming we have a reference to the root element, you can get the following information:

XElement root = ...;
XElement myItem = root.Element("MyItem");               // get the first "MyItem" element
string Host = myItem.Attribute("Host").Value;           // get value of "Host" attribute
string LastName = myItem.Attribute("LastName").Value;   // get value of "LastName" attribute
string FirstName = myItem.Attribute("FirstName").Value; // get value of "FirstName" attribute

// find "Groupe4"
XElement Groupe4 = (from g in myItem.Element("TimeStamp")
                                    .Elements("Group")
                    where g.Attribute("Name").Value == "Groupe4"
                    select g)   // only one element should be found
                   .Single();   // assign that element to variable Groupe4

// Get Value of Variable with ID = 4001
double Value4001 = (from v in Groupe4.Elements("Variable") // of all Variable elements
                    where (int)v.Attribute("ID") == 4001   // choose elements where ID = 4001
                    select (double)v.Attribute("Value"))   // select the Value
                   .Single();                              // assign that value to variable Value 4001

So to apply that to your query, you can do something like this:

XElement xmlTweets = XElement.Parse(e.Result);
var id = 4001;   // the ID to find
var toto = from tweet in xmlTweets.Descendants("MyItem")
                                  .Take(10)
           orderby (DateTime)tweet.Element("TimeStamp")
                                  .Attribute("ComputerTime") descending
           select new History {
               DisplayName = String.Format("{0} {1}",
                   tweet.Attribute("PatientFirstName").Value,
                   tweet.Attribute("PatientLastName").Value),

               // find the Variable with matching ID and get its Value as a double
               Value = (from v in tweet.Descendants("Variable")
                        where (int)v.Attribute("ID") == id
                        select (double)v.Attribute("Value"))
                       .Single()
           };

Answer 2

Once you have and XElement variable named myItemElement ,

     myItemElement
            .Element("TimeStamp")
            .Elements("Group")
            .FirstOrDefault(x => x.Attribute("Name") != null && x.Attribute("Name").Value == "Groupe4")
            .Elements("Variable")
            .FirstOrDefault(x => x.Attribute("ID") != null && x.Attribute("ID").Value == "4001")
            .Attribute("Value").Value;