Lesson 1: Using the ADO.NET Disconnected Classes in .NET framework

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Lesson 1: Using the ADO.NET Disconnected Classes
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combining two or more fields to achieve uniqueness. For example, a sales order typi cally contains line items. The primary key for each of the Line Item rows would typi cally be a combination of the order number and the line number. The PrimaryKey property must be set to an array of DataColumn objects to accommodate composite (multiple) keys. The following code shows how to set the PrimaryKey property for the Employee DataTable object:
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'VB 'Set the Primary Key
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employee.PrimaryKey = new DataColumn(){eid}
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//C# //Set the Primary Key
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employee.PrimaryKey = new DataColumn[] {eid};
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Adding Data with DataRow Objects
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After the DataTable is created with its schema, the DataTable is populated by adding DataRow objects. A DataRow object is created by a DataTable because the DataRow must conform to constraints of the DataTable object s columns.
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Adding Data to the DataTable The DataTable object contains a Rows collection, which contains a collection of DataRow objects. You can insert data into the Rows col lection by using the Add method on the Rows collection or by using the Load method on the DataTable object.
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The Add method contains an overload that accepts an array of objects instead of a DataRow object. The array of objects must match the quantity and data type of DataColumn objects in the DataTable. The Load method can be used to update existing DataRow objects or load new DataRow objects. The PrimaryKey property must be set so the DataTable object can locate the DataRow that is to be updated. The Load method expects an array of objects and a LoadOption enumeration value that has one of the following values:
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OverwriteRow
Overwrites the original DataRowVersion and the current DataRowVersion and changes the RowState to Unchanged. New rows also have the RowState of Unchanged. Overwrites the original DataRowVersion, but does not modify the current DataRowVersion. New rows have the RowState of Unchanged as well.
PreserveCurrentValues (default)
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UpdateCurrentValues
Overwrites the current DataRowVersion, but does not mod ify the original DataRowVersion. New rows have the RowState of Added. Rows that had a RowState of Unchanged have the RowState of Unchanged if the current DataRowVersion is the same as the original DataRowVersion, but if they are differ ent, the RowState is Modified.
The following code snippet demonstrates the methods of creating and adding data to the employee DataTable:
'VB 'Add New DataRow by creating the DataRow first Dim newemployee As DataRow = employee.NewRow() newemployee("Eid") = "123456789A" newemployee("FirstName") = "Nancy" newemployee("LastName") = "Davolio" newemployee("Salary") = 10.0 employee.Rows.Add(newemployee) 'Add New DataRow by simply adding the values employee.Rows.Add("987654321X", "Andrew", "Fuller", 15.0) 'Load DataRow, replacing existing contents, if existing employee.LoadDataRow( _ New Object() {"987654321X", "Janet", "Leverling", 20.0}, _ LoadOption.OverwriteChanges) //C# //Add New DataRow by creating the DataRow first DataRow newemployee = employee.NewRow(); newemployee["Eid"] = "123456789A"; newemployee["FirstName"] = "Nancy"; newemployee["LastName"] = "Davolio"; newemployee["Salary"] = 10.00m; employee.Rows.Add(newemployee); //Add New DataRow by simply adding the values employee.Rows.Add("987654321X", "Andrew", "Fuller", 15.00m); //Load DataRow, replacing existing contents, if existing employee.LoadDataRow( new object[] { "987654321X", "Janet", "Leverling", 20.00m }, LoadOption.OverwriteChanges);
This code adds new DataRow objects to the Employee DataTable. The first example explicitly creates a new DataRow using the NewRow method on the Employee DataTable. The next example adds a new DataRow by simply passing the values into the employee.Rows.Add method. Remember that nothing has been permanently stored to a database. We will cover that later in this chapter.
Lesson 1: Using the ADO.NET Disconnected Classes
Binding to the DataTable
A DataTable object is bound to any of the data-bound con trols by assigning it to the DataSource property of the data-bound control and execut ing the DataBind method of the control to render the data as follows:
'VB Protected Sub Button1_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles Button1.Click 'add grid to form
Dim gv As New GridView()
gv.Style.Add("position", "absolute")
gv.Style.Add("left", "275px")
gv.Style.Add("top", "20px")
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