Lesson 1: Using the ADO.NET Disconnected Classes in Visual Studio .NET

Paint QR Code 2d barcode in Visual Studio .NET Lesson 1: Using the ADO.NET Disconnected Classes

Lesson 1: Using the ADO.NET Disconnected Classes
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the Proposed version contains the current data and executing the GetDataRowInfo method displays the results shown in Figure 4-4.
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Figure 4-4
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The DataRow information after making changes.
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The RejectChanges method is used to roll back the DataRow to the point in time when you last called the AcceptChanges method. The AcceptChanges method overwrites the Original DataRowVersion, which means that you cannot roll back to a point in time that is earlier than the last time AcceptChanges was called.
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Explicitly Changing RowState with the SetAdded and SetModified Methods
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The SetAdded and SetModified methods on the DataRow allow you to explicitly set the RowState. This is useful when you want to force a DataRow to be stored in a data store that is different from the data store from which the DataRow was originally loaded.
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Deleting and Undeleting the DataRow The Delete method on the DataRow is used to set the RowState of the DataRow to Deleted. A DataRow object that has a RowState of Deleted indicates that the row needs to be deleted from the data store.
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There are many scenarios where you need to undelete a DataRow. The DataRow object doesn t have an undelete method, but you can use the RejectChanges method to per form an undelete that may satisfy some scenarios. The problem is that executing the RejectChanges method copies the Original DataRowVersion to the Current DataRowVersion, which effectively restores the DataRow object to its state at the time the last AcceptChanges method was executed. This means that any changes that were made to the data prior to deleting are lost.
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Copying and Cloning the DataTable
You often need to create a full copy of a DataTable in your application, possibly to pass it to another application, or to use as a scratch pad for operations that may be thrown out later. For example, you may want to assign a DataTable object to a GridView con trol to allow a user to edit the data, but you also may want to provide a cancel button that aborts all changes on the Web page. A simple way to implement this functionality is to create a copy of your DataTable object and use the copy for editing. If the user clicks the cancel button, the DataTable copy is thrown out. If the user decides to keep the changes, you can replace the original DataTable object with the edited copy. To create a copy of a DataTable object, use the Copy method on the DataTable, which copies the DataTable object s schema and data. The following code snippet shows how to invoke the Copy method:
'VB Dim copy as DataTable = employee.Copy( ) //C# DataTable copy = employee.Copy( );
You often require a copy of the DataTable schema without the data. You can accom plish this by invoking the Clone method on the DataTable. Use this method when an empty copy of the DataTable is required and to which DataRow objects will be added at a later time. The following code shows the Clone method:
'VB Dim clone as DataTable = employee.Clone( ) //C# DataTable clone = employee.Clone( );
Importing DataRow Objects into a DataTable
The ImportRow method on the DataTable object copies a DataRow from a DataTable that has the same schema. The ImportRow method also imports Current and Original version data. If you attempt to import a DataRow that has a primary key value that already exists in the DataTable object, a ConstraintException is thrown. The following code snippet shows the process for cloning the DataTable and then copying a single DataRow to the cloned copy:
'VB Dim clone as DataTable = employee.Clone( )
clone.ImportRow(employee.Rows(0))
Lesson 1: Using the ADO.NET Disconnected Classes
//C# DataTable clone = employee.Clone(); clone.ImportRow(employee.Rows[0]);
Using the DataTable with XML Data
You can use the WriteXml method of a DataTable to write the contents of the DataTable to an XML file or stream. This method should be used with the Server.MapPath method to convert a simple filename to the Web site path, as shown in the following code snippet:
'VB Protected Sub Button5_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) Handles Button5.Click
Dim employee As DataTable = GetDataTable()
employee.WriteXml(Server.MapPath("employee.xml"))
Response.Redirect("employee.xml")
End Sub //C# protected void Button5_Click(object sender, EventArgs e) { DataTable employee = GetDataTable(); employee.WriteXml(Server.MapPath("employee.xml")); Response.Redirect("employee.xml"); }
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