Creating an ASP.NET Search Engine

The structure of the Site Search Engine is as follows:

Classes

The ability to define a class and create instances of classes is one of the most important capabilities of any object-oriented language. In the coming section, we see the classes that we have used in the search module.

SiteSearch.aspx

Web Forms are one of the new, exciting features in Microsoft's .NET initiative. SiteSearch.aspx is a web form which is also the start page for the search module.

A Web Forms page consists of a page (ASPX file) and a code behind file (.aspx.cs file or .aspx.vb file). Our web form consists of SiteSearch.aspx and SiteSearch.aspx.vb. I will be treating them simultaneously touching on the main elements of the web form.

ASP.NET is an event-driven programming environment. We will see some event handlers and methods in the coming section.

Page_Load

The server controls are loaded on the Page object and the view state information is available at this point. The Page_Load event checks if sSite is nothing and assigns the Session("Site") variable to it.

      Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        If IsNothing(sSite) Then
            sSite = Session("Site")
        End If
    End Sub

srchbtn_Click

The search button event is fired when the search button is clicked. Here we put the code to change control settings or display text on the page. Here we check if the search contains text and then call the SearchSite method. DisplayContent() is called to assign values to different controls in the web page.

    '*********************************************************************
    '
    ' srchbtn_Click event
    '
    ' Add code to this event.
    '
    '*********************************************************************
    Private Sub srchbtn_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles srchbtn.Click
        Dim strSearchWords As String
        'If there is no words entered by the user to search for then dont carryout the file search routine
        pnlSearchResults.Visible = False
        strSearchWords = Trim(Request.Params("search"))

        If Not strSearchWords.Equals("") Then
            Searchs.Site.ApplicationPath = String.Format("http://{0}{1}", Request.ServerVariables("HTTP_HOST"), Request.ApplicationPath)
            sSite = SearchSite(strSearchWords)
            Session("Site") = sSite
            dgrdPages.CurrentPageIndex = 0
            DisplayContent()

        End If
    End Sub

DisplayContent

DisplayContent() is called to assign values to different controls in the web page. The DataGrid content is set by calling the BindDataGrid method. ViewState("SortExpression") is used to store the sort expression.

    '*********************************************************************
    '
    ' DisplayContent method
    '
    ' The  data is bound to the respective fields.
    '
    '*********************************************************************
    Private Sub DisplayContent()
        If Not IsNothing(sSite.PageDataset) Then
            pnlSearchResults.Visible = True
            lblSearchWords.Text = sSite.SearchWords

            If ViewState("SortExpression") Is Nothing Then
                ViewState("SortExpression") = "MatchCount Desc"
            End If

            BindDataGrid(ViewState("SortExpression"))
            lblTotalFiles.Text = sSite.TotalFilesSearched
            lblFilesFound.Text = sSite.TotalFilesFound
        End If
    End Sub

Search

The main call to the search takes place in this method. UserSearch class which we will cover shortly stores the entire search information and the result of the search. UserSearch object, i.e. srchSite is created and its properties like SearchWords and SearchCriteria assigned. Also srchSite.Search method is called.

      '************************************************************
      '
      ' SearchSite method
      '
      ' The  sSite.PageDataset is used to populate the datagrid.
      '
      '************************************************************
      Private Function SearchSite(ByVal strSearch_
                   As String) As Searchs.UserSearch
        Dim srchSite As Searchs.UserSearch
        srchSite = New Searchs.UserSearch()
        'Read in all the search words into one variable
        srchSite.SearchWords = strSearch

        If Phrase.Checked Then
            srchSite.SearchCriteria = Searchs.SearchCriteria.Phrase
        ElseIf AllWords.Checked Then
            srchSite.SearchCriteria = Searchs.SearchCriteria.AllWords
        ElseIf AnyWords.Checked Then
            srchSite.SearchCriteria = Searchs.SearchCriteria.AnyWords
        End If

        srchSite.Search(Server.MapPath("./"))
        Return srchSite
    End Function

DataGrid

The DataGrid control renders a multi-column, fully templated grid and is by far the most versatile of all data bound controls. Moreover the DataGrid control is the ASP.NET control of choice for data reporting. Hence, I have used it to display the search results. Since the focus of the article is the internal search engine, I will just give a brief overview of the features of the DataGrid used here.

Databinding

Data binding is the process of retrieving data from a source and dynamically associating it to a property of a visual element. Because a DataGrid handles (or at least has in memory) more items simultaneously, you should associate the DataGrid explicitly with a collection of data—that is, the data source.

The content of a DataGrid is set by using its DataSource property. The entire search result is stored in the sSite.PageDataset.Tables("Pages"). Hence the content of the DataGrid is set to dvwPages i.e. sSite.PageDataset.Tables("Pages").DefaultView. BindDataGrid method is called every time the page loads.

      '************************************************************
      '
      ' BindDataGrid method
      '
      ' The  sSite.PageDataset is used to populate the datagrid.
      '
      '************************************************************
      Private Sub BindDataGrid(ByVal strSortField As String)
            Dim dvwPages As DataView
            dvwPages = sSite.PageDataset.Tables("Pages").DefaultView
            dvwPages.Sort = strSortField
            dgrdPages.DataSource = dvwPages
            dgrdPages.DataBind()
      End Sub

The control has the ability to automatically generate columns that are based on the structure of the data source. Auto-generation is the default behavior of DataGrid, but you can manipulate that behavior by using a Boolean property named AutoGenerateColumns. Set the property to False when you want the control to display only the columns you explicitly add to the Columns collection. Set it to True (the default) when you want the control to add as many columns as is required by the data source. Auto-generation does not let you specify the header text, nor does it provide text formatting. Hence, here I have set it to False. You typically bind columns using the <columns> tag in the body of the <asp:datagrid> server control.

 <Columns>
  <asp:TemplateColumn>
    <ItemTemplate>
      <%# DisplayTitle(Container.DataItem( "Title" ), _
                Container.DataItem( "Path" )) %>
      <br>
      <%# Container.DataItem( "Description" ) %>
      <br>
      <span class="Path">
        <%# String.Format("{0} - {1}kb", DisplayPath(Container.DataItem( "Path" )) ,Container.DataItem( "Size" ))%>
      </span>
      <br>
      <br>
    </ItemTemplate>
  </asp:TemplateColumn>
</Columns>

DisplayTitle method and DisplayPath method are used to display customized information to the columns in the DataGrid.

      '****************************************
      '
      ' DisplayTitle method
      '
      ' Display title of searched pages 
      '
      '****************************************
      Protected Function DisplayTitle(ByVal Title _ 
              As String, ByVal Path As String) As String
            Return String.Format("<A href="{1}">{0}</A>", Title, Path)
      End Function

      '****************************************
      '
      ' DisplayPath method
      '
      ' Path of the file is returned 
      '
      '****************************************
      Protected Function DisplayPath(ByVal Path As String) As String
            Return String.Format("{0}{1}/{2}", _ 
              Request.ServerVariables("HTTP_HOST"), _ 
              Request.ApplicationPath, Path)
      End Function

Pagination

Unlike the DataList control, the DataGrid control supports data pagination, that is, the ability to divide the displayed data source rows into pages. The size of our data source easily exceeds the page real estate. So to preserve scalability on the server and to provide a more accessible page to the user, you display only a few rows at a time. To enable pagination of the DataGrid control, you need to tell the control about it. You do this through the AllowPaging property.

The pager bar is an interesting and complimentary feature offered by the DataGrid control to let users easily move from page to page. The pager bar is a row displayed at the bottom of the DataGrid control that contains links to available pages. When you click any of these links, the control automatically fires the PageIndexChanged event and updates the page index accordingly. dgrdPages_PageIndexChanged is called when the page index changes.

      '*****************************************************************
      '
      ' dgrdPages_PageIndexChanged event
      '
      ' The CurrentPageIndex is Assigned the page index value.
      ' The datagrid is then populated using the BindDataGrid function.
      '
      '*****************************************************************
      Protected Sub dgrdPages_PageIndexChanged(ByVal s As Object, _ 
          ByVal e As DataGridPageChangedEventArgs) _ 
          Handles dgrdPages.PageIndexChanged
      dgrdPages.CurrentPageIndex = e.NewPageIndex
      DisplayContent()
      End Sub

You control the pager bar by using the PagerStyle property’s Mode attribute. Values for the Mode attribute come from the PagerMode enumeration. Here we have chosen a detailed series of numeric buttons, each of which points to a particular page.

<PagerStyle CssClass="GridPager" Mode="NumericPages"></PagerStyle>

Sorting

The DataGrid control does not actually sort rows, but it provides good support for sorting as long as the sorting capabilities of the underlying data source are adequate. The data source is always responsible for returning a sorted set of records based on the sort expression selected by the user through the DataGrid control’s user interface. The built-in sorting mechanism is triggered by setting the AllowSorting property to True.

dgrdPages_SortCommand is called to sort the DataGrid. The SortCommand event handler knows about the sort expression through the SortExpression property, which is provided by the DataGridSortCommandEventArgs class. In our code, the sort information is persisted because it is stored in a slot in the page’s ViewState collection.

Note: In my pages, I have disabled the header but if the header is shown, you can use it to sort the DataGrid.

      '*****************************************************************
      '
      ' dgrdAdditionalItems_SortCommand event
      '
      ' The ViewState( "SortExpression" ) is Assigned
      ' the sort expression value.
      ' The datagrid is then populated using the BindDataGrid function.
      '
      '*****************************************************************
      Protected Sub dgrdPages_SortCommand(ByVal s As Object, _ 
             ByVal e As DataGridSortCommandEventArgs) _ 
             Handles dgrdPages.SortCommand
            ViewState("SortExpression") = e.SortExpression
            DisplayContent()
      End Sub