Writing a LINQ query on an XML data file: Step by step explanation in VB.NET (VS2008)

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Introduction

I had to create a working prototype of a web project. I mocked up screens, created some fake data in an XML file, showed it on screens. Now, I wanted to work on the data (query XML file and present on other screens). I know that it’s achievable through LINQ. I searched for snippets online. I was able to find some help, but had to spend a lot of time. This led me to post this topic. Hope it would be helpful for a few beginners.

Using the code

Included is a Zip file containing the two ASP pages and an XML file. Feel free to use them. I am not going to explain anything here. Instead, I shall show you the step by step process to create the project, and you can go through the code.

Open VS 2008. Create a new web project by selecting the ASP.NET Web Site template. I name the project, “LinqDemo”. Select the language as “VisualBasic” and .NET framework 3.5.

Delete the default.aspx page. Add a new form, Employee.aspx, and set it as the start page. Modify the code for the page, Employee.aspx, to show as follows:

Employee.aspx:

Add the Employee.xml file to the App_Data folder in your project. Modify the file to show data as follows:

Modify the Employee.aspx.vb file to show the following code:

Partial Class Employee
    Inherits System.Web.UI.Page

    Protected Sub Page_Load(ByVal sender As Object, _
              ByVal e As System.EventArgs) Handles Me.Load
        If Not Page.IsPostBack Then
            BindGrid()
        End If
    End Sub

    Private Sub BindGrid()
        Dim xmlDS As New XmlDataSource
        xmlDS.DataFile = "~/App_Data/Employee.xml"
        xmlDS.XPath = ".//Employee/ROW"
        gvEmployee.DataSource = xmlDS
        gvEmployee.DataBind()
    End Sub
End Class

At this point, you should be able to build and Run the project. You should be able to see a page with the employee data in a grid.

When the Details button is clicked, we want to show some data on a new page. I am not doing anything incredible. I am just showing the same data in the grid in a new page.

Add a new page, and call it EmpDetails.aspx. Modify the page, to show as follows

EmpDetails.aspx:

Modify Employee.aspx.vb to show as follows:

Employee.aspx.vb:

Partial Class Employee
    Inherits System.Web.UI.Page

    Protected Sub Page_Load(ByVal sender As Object, _
              ByVal e As System.EventArgs) Handles Me.Load
        If Not Page.IsPostBack Then
            BindGrid()
        End If
    End Sub

    Private Sub BindGrid()
        Dim xmlDS As New XmlDataSource
        xmlDS.DataFile = "~/App_Data/Employee.xml"
        xmlDS.XPath = ".//Employee/ROW"
        gvEmployee.DataSource = xmlDS
        gvEmployee.DataBind()
    End Sub

    Protected Sub gvEmployee_SelectedIndexChanged(ByVal sender As Object, _
              ByVal e As System.EventArgs) Handles gvEmployee.SelectedIndexChanged
        Session("EMPID") = gvEmployee.SelectedRow.Cells(0).Text
        Response.Redirect("EmpDetails.aspx")
    End Sub
End Class

Modify the EmpDetails.aspx.vb page to show as follows:

EmpDetails.aspx.vb:

Partial Class EmpDetails
    Inherits System.Web.UI.Page

    Protected Sub Page_Load(ByVal sender As Object, _
              ByVal e As System.EventArgs) Handles Me.Load
        If Not Page.IsPostBack Then
            BindData()
        End If
    End Sub

    Private Sub BindData()
        Dim pk As Integer
        pk = CInt(Session("EMPID"))

        Dim xmlDS = XElement.Load(Request.PhysicalApplicationPath & _
                                  "/App_Data/Employee.xml")
        Dim query = From row In xmlDS.Elements Where _
                   (CType(row.Attribute("empno"), Integer) = pk) Select row

        For Each row As XElement In query
            lblEmpNo.Text = row.Attribute("empno")
            lblEmpName.Text = row.Attribute("ename")
            lblJob.Text = row.Attribute("job")
            lblHireDt.Text = row.Attribute("hiredate")
            lblSal.Text = row.Attribute("sal")
            lblDeptNo.Text = row.Attribute("deptno")
            lblDeptName.Text = row.Attribute("dname")
            lblLoc.Text = row.Attribute("loc")
        Next
    End Sub

    Protected Sub btnBack_Click(ByVal sender As Object, _
              ByVal e As System.EventArgs) Handles btnBack.Click
        Response.Redirect("Employee.aspx")
    End Sub
End Class

Run the project, and you should be able to click on Details, which will show the data returned from LINQ.

This is the first article I am posting. Reviews would be helpful for my future posts. Thanks.