CODEWITHSUNDEEP
asp.netvb.netlinqasp.net-4.5
EvilDr
EvilDr

Reputation: 9610

Read values from XDocument

I need to enumerate an XML (XDocument) document as such...

<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<applied>
  <ah ID="8298" userId="87459" roleId="2700" />
  <ah ID="8300" userId="87459" roleId="2699" />
  <ah ID="8299" userId="87460" roleId="2700" />
</applied>

...and extract all the values of userID and roleID into two separate StringBuilder objects.

I've been messing about with Linq for the first time, but am struggling, and would appreciate some help please (this is a VB webforms app). I have seen lots of Linq example that get a single value, but not two at the same time in the manner I need.

Also, this XML file could be up to 100,000 rows in length. Is Linq more memory efficient than, say, a FOR EACH loop? If not, could someone please provide a FOR EACH example?

Thanks in advance.

Update: The result would be:

Userids = "87459,87459,87460"
roleIds = "2700,2699,2700"

Upvotes: 0

Views: 326

Answers (1)

djv
djv

Reputation: 15774

First, you need to get the xml from your file system into memory. This is called deserialization. My preferred method of doing this is using a model for the xml, which is just a class with some attributes to tell the xml serializer how to parse the file:

<XmlRoot("applied")> _
Public Class Applied
    <XmlElement("ah")> _
    Public Property AhList As List(Of Ah)
End Class

Public Class Ah
    <XmlAttribute("ID")> _
    Public Property ID As Integer
    <XmlAttribute("userID")> _
    Public Property UserID As Integer
    <XmlAttribute("roleID")> _
    Public Property RoleID As Integer
End Class

Note that the XmlAttribute tells the serializer exactly what the attribute is called in xml, but you may use any name for it in the model, i.e. <XmlAttribute("userID")> Public Property UserID As Integer.

Now that you have this model, you need to deserialize from xml.

Dim appls As New Applied()
Dim serializer As XmlSerializer = Nothing
serializer = New XmlSerializer(GetType(Applied))
appl = serializer.Deserialize(xd.CreateReader()) ' xd is your XDocument

Now you should have all the xml deserialized into the appls object. This object has a property, according to the model, called AhList, which is a list of all the elements in your xml. Since List(Of Ah) is IEnumerable, you can use LINQ on it.

Upvotes: 1

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