Assembly: System.Web (in system.web.dll)
ASP.NET supports a data-binding architecture that enables Web server controls to bind to data in a consistent fashion. Web server controls that bind to data are referred to as data-bound controls, and the classes that facilitate that binding are called data source controls. Data source controls can represent any data source: a relational database, a file, a stream, a business object, and so on. Data source controls present data in a consistent way to data-bound controls, regardless of the source or format of the underlying data.
You use the data source controls that are provided with ASP.NET, including SqlDataSource, AccessDataSource, and XmlDataSource, to perform most Web development tasks. You use the base DataSourceControl and DataSourceView classes when you want to implement your own custom data source control.
You can think of a data source control as the combination of the IDataSource object and its associated lists of data, called data source views. Each list of data is represented by a DataSourceView object. The DataSourceView class is the base class for all data source views, or lists of data, associated with data source controls. Data source views define the capabilities of a data source control. Because the underlying data storage contains one or more lists of data, a data source control is always associated with one or more named data source views. The data source control uses the GetViewNames method to enumerate the data source views currently associated with the data source control and the GetView method to retrieve a specific data source view instance by name.
All DataSourceView objects support data retrieval from the underlying data source using the ExecuteSelect method. All views optionally support a basic set of operations, including operations such as ExecuteInsert, ExecuteUpdate, and ExecuteDelete. A data-bound control can discover the capabilities of a data source control by retrieving an associated data source view using the GetView and GetViewNames methods, and by querying the view at design time or run time.
The following code example demonstrates how to extend the DataSourceView class to create a strongly typed view class for a data source control. The
CsVDataSourceView class defines the capabilities of the
CsvDataSource data source control and provides an implementation for data-bound controls to use data stored in comma-separated value (.csv) files. For more information on the
CsvDataSource data source control, see the DataSourceControl class.
' The CsvDataSourceView class encapsulates the ' capabilities of the CsvDataSource data source control. Public Class CsvDataSourceView Inherits DataSourceView Public Sub New(owner As IDataSource, name As String) MyBase.New(owner, DefaultViewName) End Sub 'New ' The data source view is named. However, the CsvDataSource ' only supports one view, so the name is ignored, and the ' default name used instead. Public Shared DefaultViewName As String = "CommaSeparatedView" ' The location of the .csv file. Private aSourceFile As String = [String].Empty Friend Property SourceFile() As String Get Return aSourceFile End Get Set ' Use MapPath when the SourceFile is set, so that files local to the ' current directory can be easily used. Dim mappedFileName As String mappedFileName = HttpContext.Current.Server.MapPath(value) aSourceFile = mappedFileName End Set End Property ' Do not add the column names as a data row. Infer columns if the CSV file does ' not include column names. Private columns As Boolean = False Friend Property IncludesColumnNames() As Boolean Get Return columns End Get Set columns = value End Set End Property ' Get data from the underlying data source. ' Build and return a DataView, regardless of mode. Protected Overrides Function ExecuteSelect(selectArgs As DataSourceSelectArguments) _ As System.Collections.IEnumerable Dim dataList As IEnumerable = Nothing ' Open the .csv file. If File.Exists(Me.SourceFile) Then Dim data As New DataTable() ' Open the file to read from. Dim sr As StreamReader = File.OpenText(Me.SourceFile) Try ' Parse the line Dim dataValues() As String Dim col As DataColumn ' Do the following to add schema. dataValues = sr.ReadLine().Split(","c) ' For each token in the comma-delimited string, add a column ' to the DataTable schema. Dim token As String For Each token In dataValues col = New DataColumn(token, System.Type.GetType("System.String")) data.Columns.Add(col) Next token ' Do not add the first row as data if the CSV file includes column names. If Not IncludesColumnNames Then data.Rows.Add(CopyRowData(dataValues, data.NewRow())) End If ' Do the following to add data. Dim s As String Do s = sr.ReadLine() If Not s Is Nothing Then dataValues = s.Split(","c) data.Rows.Add(CopyRowData(dataValues, data.NewRow())) End If Loop Until s Is Nothing Finally sr.Close() End Try data.AcceptChanges() Dim dataView As New DataView(data) If Not selectArgs.SortExpression Is String.Empty Then dataView.Sort = selectArgs.SortExpression End If dataList = dataView Else Throw New System.Configuration.ConfigurationErrorsException("File not found, " + Me.SourceFile) End If If dataList is Nothing Then Throw New InvalidOperationException("No data loaded from data source.") End If Return dataList End Function 'ExecuteSelect Private Function CopyRowData([source]() As String, target As DataRow) As DataRow Try Dim i As Integer For i = 0 To [source].Length - 1 target(i) = [source](i) Next i Catch iore As IndexOutOfRangeException ' There are more columns in this row than ' the original schema allows. Stop copying ' and return the DataRow. Return target End Try Return target End Function 'CopyRowData ' The CsvDataSourceView does not currently ' permit deletion. You can modify or extend ' this sample to do so. Public Overrides ReadOnly Property CanDelete() As Boolean Get Return False End Get End Property Protected Overrides Function ExecuteDelete(keys As IDictionary, values As IDictionary) As Integer Throw New NotSupportedException() End Function 'ExecuteDelete ' The CsvDataSourceView does not currently ' permit insertion of a new record. You can ' modify or extend this sample to do so. Public Overrides ReadOnly Property CanInsert() As Boolean Get Return False End Get End Property Protected Overrides Function ExecuteInsert(values As IDictionary) As Integer Throw New NotSupportedException() End Function 'ExecuteInsert ' The CsvDataSourceView does not currently ' permit update operations. You can modify or ' extend this sample to do so. Public Overrides ReadOnly Property CanUpdate() As Boolean Get Return False End Get End Property Protected Overrides Function ExecuteUpdate(keys As IDictionary, _ values As IDictionary, _ oldValues As IDictionary) As Integer Throw New NotSupportedException() End Function 'ExecuteUpdate End Class 'CsvDataSourceView