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DataSourceView Class

Serves as the base class for all data source view classes, which define the capabilities of data source controls.

Namespace: System.Web.UI
Assembly: System.Web (in system.web.dll)

public abstract class DataSourceView
public abstract class DataSourceView
public abstract class DataSourceView
Not applicable.

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 : DataSourceView
{

    public CsvDataSourceView(IDataSource owner, string name) :base(owner, DefaultViewName) {

    }

    // 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 static string DefaultViewName = "CommaSeparatedView";

    // The location of the .csv file.
    private string sourceFile = String.Empty;
    internal string SourceFile {
        get {
            return sourceFile;
        }
        set {
            // Use MapPath when the SourceFile is set, so that files local to the
            // current directory can be easily used.
            string mappedFileName = HttpContext.Current.Server.MapPath(value);
            sourceFile = mappedFileName;
        }
    }

    // Do not add the column names as a data row. Infer columns if the CSV file does
    // not include column names.
    private bool columns = false;
    internal bool IncludesColumnNames {
        get {
            return columns;
        }
        set {
            columns = value;
        }
    }

    // Get data from the underlying data source.
    // Build and return a DataView, regardless of mode.
    protected override IEnumerable ExecuteSelect(DataSourceSelectArguments selectArgs) {
        IEnumerable dataList = null;
        // Open the .csv file.
        if (File.Exists(this.SourceFile)) {
            DataTable data = new DataTable();

            // Open the file to read from.
            using (StreamReader sr = File.OpenText(this.SourceFile)) {
                // Parse the line
                string s = "";
                string[] dataValues;
                DataColumn col;

                // Do the following to add schema.
                dataValues = sr.ReadLine().Split(',');
                // For each token in the comma-delimited string, add a column
                // to the DataTable schema.
                foreach (string token in dataValues) {
                    col = new DataColumn(token,typeof(string));
                    data.Columns.Add(col);
                }

                // Do not add the first row as data if the CSV file includes column names.
                if (! IncludesColumnNames)
                    data.Rows.Add(CopyRowData(dataValues, data.NewRow()));

                // Do the following to add data.
                while ((s = sr.ReadLine()) != null) {
                    dataValues = s.Split(',');
                    data.Rows.Add(CopyRowData(dataValues, data.NewRow()));
                }
            }
            data.AcceptChanges();
            DataView dataView = new DataView(data);
            if (selectArgs.SortExpression != String.Empty) {
                dataView.Sort = selectArgs.SortExpression;
            }
            dataList = dataView;
        }
        else {
            throw new System.Configuration.ConfigurationErrorsException("File not found, " + this.SourceFile);
        }

        if (null == dataList) {
            throw new InvalidOperationException("No data loaded from data source.");
        }

        return dataList;
    }

    private DataRow CopyRowData(string[] source, DataRow target) {
        try {
            for (int i = 0;i < source.Length;i++) {
                target[i] = source[i];
            }
        }
        catch (System.IndexOutOfRangeException) {
            // There are more columns in this row than
            // the original schema allows.  Stop copying
            // and return the DataRow.
            return target;
        }
        return target;
    }
    // The CsvDataSourceView does not currently
    // permit deletion. You can modify or extend
    // this sample to do so.
    public override bool CanDelete {
        get {
            return false;
        }
    }
    protected override int ExecuteDelete(IDictionary keys, IDictionary values)
    {
        throw new NotSupportedException();
    }
    // The CsvDataSourceView does not currently
    // permit insertion of a new record. You can
    // modify or extend this sample to do so.
    public override bool CanInsert {
        get {
            return false;
        }
    }
    protected override int ExecuteInsert(IDictionary values)
    {
        throw new NotSupportedException();
    }
    // The CsvDataSourceView does not currently
    // permit update operations. You can modify or
    // extend this sample to do so.
    public override bool CanUpdate {
        get {
            return false;
        }
    }
    protected override int ExecuteUpdate(IDictionary keys, IDictionary values, IDictionary oldValues)
    {
        throw new NotSupportedException();
    }
}

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Windows 98, Windows Server 2000 SP4, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 3.0, 2.0

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