Linq to XML Help

Question

Hi I have the following xml file that I am wanting to use:

<?xml version="1.0" encoding="utf-8"?>

<Roles>

    <Role name="Admin">

        <user>user1</user>

        <user>user2</user>

    </Role>

    <Role name="User">

        <user>user1</user>

        <user>user2</user>

        <user>user3</user>

    </Role>

    <Role name="Guest">

        <user>user4</user>

        <user>user5</user>

    </Role>

    <Role name="Power User">

        <user>user3</user>

    </Role>

</Roles>

I have the following class with this:

Public Class Role

        Public RoleName As String

        Public AssignedUsers As New StringCollection()

End Class

I am using the following code to try and fill the object/class created with the data from the xml file:  

Dim doc As XDocument = XDocument.Load(fileName)



                    Dim query = From xElem In doc.Descendants("Role") Select New With { _

                                .RoleName = xElem.Attribute("name").Value, _

                                .AssignedUsers = xElem.Element("user").Value}



                    _Roles = query

_Roles is declared with the following:

Private _Roles As List(Of Role)

The query works to an extent that it selects all the roles and JUST one user but will not allow itself to be placed into the object. I have tried a Directcast the the object but that does not work either!

Can anyone see where I am going wrong in placing the query in the store I am using for the roles within my app I am trying but at this moement failing miserably to create!??

Thanks!

Tuppers

Answer 1

For starters, you're creating an anonymous type.  Note you haven't specified the type after "New" in your select statement.  Change it to this:

Dim query = From xElem In doc.Descendants("Role") Select New Role With { _
            .RoleName = xElem.Attribute("name").Value, _
            .AssignedUsers = xElem.Element("user").Value}

Next, you need to check the type of the AssignedUsers property.  It's currently StringCollection.  Change it to a List(Of String).  It should now look like this:

Public Class Role
    Public RoleName As String
    Public AssignedUsers As List(Of String)
End Class

Next, we're going to change what we're getting from the query again.  This query modifies the one above, and is the final revision:

Dim query = From xElem In doc.Descendants("Role") Select New Role With { _
            .RoleName = xElem.Attribute("name").Value, _
            .AssignedUsers = xElem.Elements("user").Select(Function(x) x.Value).ToList()}

Now, LINQ queries return an IEnumerable(Of T), not a List(Of T), so you have two options here.  Either change the type of _Roles to an IEnumerable(Of Role), or use the .ToList() method off of query to convert the IEnumerable(Of T) to a List(Of T):

_Roles = query.ToList();

Make those changes, and it should work fine. 

---

Coding Light - Illuminated Ideas and Algorithms in Software
Coding Light Wiki • LinkedIn • ForumsBrowser

Answer 2

I wouldn't use a StringCollection in .NET 3.5 code. Why don't you use a List<string> e.g.

Public Class Role

    Private _roleName As String

    Public Property RoleName() As String
        Get
            Return _roleName
        End Get
        Set(ByVal value As String)
            _roleName = value
        End Set
    End Property

    Private _assignedUsers As List(Of String)

    Public Property AssignedUsers() As List(Of String)
        Get
            Return _assignedUsers
        End Get
        Set(ByVal value As List(Of String))
            _assignedUsers = value
        End Set
    End Property

End Class

        Dim doc As XDocument = XDocument.Load(FileName)
        Dim query As IEnumerable(Of Role) = _
        From role In doc.Root.Elements("Role") _
        Select New Role With { _
        .RoleName = CType(role.Attribute("name"), String), _
        .AssignedUsers = role.Elements("user").Select(Function(u) CType(u, String)).ToList() _
        }

        _Roles = query.ToList()

---

MVP XML My blog

Answer 3

Super thanks for that!! I do have a few questions on what just happened! but i have no time at the mo to really digest I will repost more than likely tomorrow!

again thankyou! I am still learning! sorry!

Tuppers 

Answer 4

Hi thanks for that yesterday I have a question about this part:

.AssignedUsers = role.Elements("user").Select(Function(u) CType(u, String)).ToList()

the select statement used here. I get that this selects the list of users within the role element. I have not seen this before could you please explain or point me in the direction of a good book for linq for this as well as in general and/or some online articles using this?

thanks again!

Answer 5

See the VB documentation on lamba expressions . With LINQ you have, for some queries, the choice between the query syntax and the method syntax. So
role.Elements("user").Select(Function(u) CType(u, String))
is the same as
From user In role.Elements("user") Select CType(u, String)

---

MVP XML My blog

Answer 6

Thanks your help is much appreciatted.

I am now having a problem with the following code as I have changed from the stringcollection to the List(Of String):

Public Overrides Function GetAllRoles() As String()
            Try
                Dim Results As String() = New String(CurrentStore.Roles.Count) {}
                For i As Integer = 0 To i < Results.Length
                    Results(i) = CurrentStore.Roles(i).RoleName
                Next
                Return Results
            Catch ex As Exception
                Throw
            End Try
        End Function

i think I should return an arry of results but I am not sure about changing the logic to get there.

Could you possibly help please?

regards

Tuppers and again thanks! Sorry if i should of created a new post!

Answer 7

I have tried something like:

 

Public Overrides Function GetAllRoles() As String()
            Try
                Dim Results As New List(Of String)
                Dim Role As List(Of Role) = CurrentStore.Roles
                If Role IsNot Nothing Then
                    For Each r In Role
                         NOT SURE WHAT TO PUT HERE!!!
                    Next

                Else
                    Throw New ProviderException("There are no roles to diplay!")
                End If
                Return Results.ToArray()
            Catch ex As Exception
                Throw
            End Try
        End Function

As you can see I am not sure what to place in the for loop!

 

 

Answer 8

What is CurrentStore.Roles exactly? A List(Of Role)? If you want an array of role names then you can simply do
Return CurrentStore.Roles.Select(Function(r) r.RoleName).ToArray()
or if you prefer query syntax then e.g.
Return (From role In CurrentStore.Roles Select role.RoleName).ToArray()

---

MVP XML My blog

Answer 9

what can I say! thank you and thank you some more I should be able to move on quite a bit from here I think!! I do have some questions about handling multiple updates on an xml file but I will post that in he XML forum!

and thank you!

do you recommend any books for vb or linq? its nice sometimes to get away from the computer screen!

Cheers

Tuppers