IDataSource Interfaccia

Definizione

Rappresenta un'origine dati astratta alla quale stabiliscono un'associazione i controlli con associazione a dati.

public interface class IDataSource
public interface IDataSource
type IDataSource = interface
Public Interface IDataSource
Derivato

Esempio

Nell'esempio di codice seguente viene illustrato come una classe può implementare i metodi definiti dall'interfaccia per IDataSource fornire dati ai controlli con associazione a dati. Il controllo origine dati in questo esempio funge da origine dati in un file con valori delimitati da virgole e può essere usato da qualsiasi controllo associato a dati per visualizzare dati di file delimitati da virgole. Questo esempio di codice fa parte di un esempio più esaustivo fornito per la DataSourceControl classe .

using System;
using System.Collections;
using System.Data;
using System.IO;
using System.Security.Permissions;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

// The CsvDataSource is a data source control that retrieves its
// data from a comma-separated value file.
[AspNetHostingPermission(SecurityAction.Demand, Level=AspNetHostingPermissionLevel.Minimal)]
public class CsvDataSource : DataSourceControl
{
    public CsvDataSource() : base() {}

    // The comma-separated value file to retrieve data from.
    public string FileName {
        get {
            return ((CsvDataSourceView)this.GetView(String.Empty)).SourceFile;
        }
        set {
            // Only set if it is different.
            if ( ((CsvDataSourceView)this.GetView(String.Empty)).SourceFile != value) {
                ((CsvDataSourceView)this.GetView(String.Empty)).SourceFile = value;
                RaiseDataSourceChangedEvent(EventArgs.Empty);
            }
        }
    }

    // Do not add the column names as a data row. Infer columns if the CSV file does
    // not include column names.
    public bool IncludesColumnNames {
        get {
            return ((CsvDataSourceView)this.GetView(String.Empty)).IncludesColumnNames;
        }
        set {
            // Only set if it is different.
            if ( ((CsvDataSourceView)this.GetView(String.Empty)).IncludesColumnNames != value) {
                ((CsvDataSourceView)this.GetView(String.Empty)).IncludesColumnNames = value;
                RaiseDataSourceChangedEvent(EventArgs.Empty);
            }
        }
    }

    // Return a strongly typed view for the current data source control.
    private CsvDataSourceView view = null;
    protected override DataSourceView GetView(string viewName) {
        if (null == view) {
            view = new CsvDataSourceView(this, String.Empty);
        }
        return view;
    }
    // The ListSourceHelper class calls GetList, which
    // calls the DataSourceControl.GetViewNames method.
    // Override the original implementation to return
    // a collection of one element, the default view name.
    protected override ICollection GetViewNames() {
        ArrayList al = new ArrayList(1);
        al.Add(CsvDataSourceView.DefaultViewName);
        return al as ICollection;
    }
}

// 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 (!string.IsNullOrEmpty(selectArgs.SortExpression)) {
                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();
    }
}
Imports System.Collections
Imports System.Data
Imports System.IO
Imports System.Security.Permissions
Imports System.Web
Imports System.Web.UI
Imports System.Web.UI.WebControls

Namespace Samples.AspNet.VB.Controls

' The CsvDataSource is a data source control that retrieves its
' data from a comma-separated value file.
<AspNetHostingPermission(SecurityAction.Demand, Level:=AspNetHostingPermissionLevel.Minimal)> _
Public Class CsvDataSource
   Inherits DataSourceControl

   Public Sub New()
   End Sub

   ' The comma-separated value file to retrieve data from.
   Public Property FileName() As String
      Get
         Return CType(Me.GetView([String].Empty), CsvDataSourceView).SourceFile
      End Get
      Set
         ' Only set if it is different.
         If CType(Me.GetView([String].Empty), CsvDataSourceView).SourceFile <> value Then
            CType(Me.GetView([String].Empty), CsvDataSourceView).SourceFile = value
            RaiseDataSourceChangedEvent(EventArgs.Empty)
         End If
      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.

   Public Property IncludesColumnNames() As Boolean
      Get
         Return CType(Me.GetView([String].Empty), CsvDataSourceView).IncludesColumnNames
      End Get
      Set
         ' Only set if it is different.
         If CType(Me.GetView([String].Empty), CsvDataSourceView).IncludesColumnNames <> value Then
            CType(Me.GetView([String].Empty), CsvDataSourceView).IncludesColumnNames = value
            RaiseDataSourceChangedEvent(EventArgs.Empty)
         End If
      End Set
   End Property


   ' Return a strongly typed view for the current data source control.
   Private view As CsvDataSourceView = Nothing

   Protected Overrides Function GetView(viewName As String) As DataSourceView
      If view Is Nothing Then
         view = New CsvDataSourceView(Me, String.Empty)
      End If
      Return view
   End Function 'GetView

   ' The ListSourceHelper class calls GetList, which
   ' calls the DataSourceControl.GetViewNames method.
   ' Override the original implementation to return
   ' a collection of one element, the default view name.
   Protected Overrides Function GetViewNames() As ICollection
      Dim al As New ArrayList(1)
      al.Add(CsvDataSourceView.DefaultViewName)
      Return CType(al, ICollection)
   End Function 'GetViewNames

End 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

   ' 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
End Namespace

Commenti

ASP.NET supporta un'architettura di data binding dei controlli che consente ai controlli server Web di eseguire l'associazione ai dati in modo coerente. I controlli server Web associati ai dati sono detti controlli associati a dati e le classi che facilitano tale associazione sono denominate controlli origine dati. I controlli origine dati possono rappresentare qualsiasi origine dati: un database relazionale, un file, un flusso, un oggetto business e così via. I controlli origine dati presentano i dati in modo coerente ai controlli associati a dati, indipendentemente dall'origine o dal formato dei dati sottostanti.

L'interfaccia IDataSource viene implementata quando si vuole implementare un controllo origine dati personalizzato ASP.NET origine dati.

Qualsiasi classe che implementa IDataSource l'interfaccia è un controllo origine dati. L'interfaccia funge da base per tutti i controlli origine dati ASP.NET e definisce uno dei concetti fondamentali dell'architettura di data binding con i due metodi seguenti: il metodo e IDataSource GetView il metodo GetViewNames . Questo concetto è che tutti i controlli origine dati supportano una o più viste denominate nei dati. L'oggetto vista origine dati è simile DataView all'astrazione nello spazio dei nomi : una visualizzazione personalizzata e associabile ai dati per l'ordinamento, il filtro e altre operazioni sui dati definite dalla System.Data vista. Nella sua base, un controllo origine dati non esegue altro che recuperare le visualizzazioni sui dati.

Un controllo origine dati può avere uno o più oggetti vista origine dati associati. Alcuni controlli origine dati, inclusi quelli che rappresentano database relazionali come SqlDataSource e AccessDataSource , supportano una sola visualizzazione. Altri controlli origine dati, inclusi i controlli origine dati gerarchici, ad esempio SiteMapDataSource , supportano molte visualizzazioni. La vista origine dati definisce le funzionalità di un'origine dati e le operazioni supportate.

In sintesi, i controlli origine dati implementano l'interfaccia , supportano una o più viste denominate sui dati che rappresentano e supportano sempre il recupero dei dati IDataSource dall'origine dati che rappresentano. I controlli origine dati recuperano sempre i dati su richiesta, ad esempio quando DataBind viene chiamato su un controllo associato a dati.

Metodi

GetView(String)

Ottiene la visualizzazione origine dati denominata associata al controllo origine dati.

GetViewNames()

Ottiene un insieme di nomi che rappresentano l'elenco di oggetti visualizzazione associati all'interfaccia IDataSource.

Eventi

DataSourceChanged

Si verifica quando un controllo origine dati ha subito una qualsiasi modifica che influisce su controlli con associazione a dati.

Metodi di estensione

GetDefaultValues(IDataSource)

Ottiene l'insieme di valori predefiniti per l'origine dati specificata.

GetMetaTable(IDataSource)

Ottiene i metadati per una tabella nell'oggetto origine dati specificato.

TryGetMetaTable(IDataSource, MetaTable)

Determina se sono disponibili i metadati della tabella.

Si applica a

Vedi anche