IDataSource Interface
Definition
Important
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Represents an abstract data source that data-bound controls bind to.
public interface class IDataSourcepublic interface IDataSourcetype IDataSource = interfacePublic Interface IDataSource- Derived
Examples
The following code example demonstrates how a class can implement the methods defined by the IDataSource interface to provide data to data-bound controls. The data source control in this example acts as a data source on a comma-separated value file, and can be used by any data-bound control to display comma-separated file data. This code example is part of a larger example provided for the DataSourceControl class.
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
Remarks
ASP.NET supports a control 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 implement the IDataSource interface when you want to implement your own custom ASP.NET data source control.
Any class that implements the IDataSource interface is a data source control. The IDataSource interface serves as the foundation for all ASP.NET data source controls and defines one of the fundamental data-binding architecture concepts with its two methods: the GetView method and the GetViewNames method. This concept is that all data source controls support one or more named views on their data. The data source view object is similar to the DataView abstraction in the System.Data namespace: a data-bindable, customized view of data for sorting, filtering, and other data operations that the view defines. At its core, a data source control does nothing more than retrieve views on data.
A data source control can have one or more associated data source view objects. Some data source controls, including those that represent relational databases such as SqlDataSource and AccessDataSource, support only one view. Other data source controls, including hierarchical data source controls such as SiteMapDataSource, support many views. The data source view defines the capabilities of a data source and the operations that it supports.
In summary, data source controls implement the IDataSource interface, support one or more named views on the data they represent, and always support data retrieval from the data source they represent. Data source controls always retrieve data on demand, such as when DataBind is called on a data bound control.
Methods
| GetView(String) |
Gets the named data source view associated with the data source control. |
| GetViewNames() |
Gets a collection of names representing the list of view objects associated with the IDataSource interface. |
Events
| DataSourceChanged |
Occurs when a data source control has changed in some way that affects data-bound controls. |
Extension Methods
| GetDefaultValues(IDataSource) |
Gets the collection of the default values for the specified data source. |
| GetMetaTable(IDataSource) |
Gets the metadata for a table in the specified data source object. |
| TryGetMetaTable(IDataSource, MetaTable) |
Determines whether table metadata is available. |
