Tài liệu Add and Delete Rows in a Dataset with ADO.NET pdf

4.2 Add and Delete Rows in a Dataset with ADO.NET Again using the OleDbDataAdapter and OleDbCommandBuilder objects, this How-To shows you how to use unbound controls with the dataset to add and delete rows from SQL Server. As with editing and updating data, you need to be able to add and delete rows using the dataset. How do you perform this task? Technique The main difference between this technique and the previous one will be which action command you will use with the DataAdapter object. You will also be presented with the Add method on the Rows collection. Steps Open and run the VB.NET-Chapter 4 solution. From the main form, click on the command button with the caption How-To 4.2. When the form loads, click on the Load List button to display the customers that begin with the letter A. Click the Add button. You will notice that the fields have now taken on a sunken look and that they are cleared. Fill in the Customer ID and Company Name text boxes with AAA1 and Another Example. Now click Save. If you move off the record and move back on, you will notice that the value has been saved. Now select the new record you added, and click the Delete button. The record disappears, and the list box is updated to reflect the deletion. 1. Make a copy of the form you created in the last How-To. 2. Add two buttons for adding and deleting records, setting the properties as listed here in Table 4.3. Table 4.3. Add and Delete Buttons Property Settings Object Property Setting Button Name Caption btnAdd &Add Button Name Text btnDelete &Delete 3. Add the following line of code where you placed the other module-level variable declarations. This variable will be set to True in the btnAdd click event, and it can be used when saving the record. 4. Dim mblnAdd As Boolean 5. Enter the following code to the Click event btnAdd. The first task is to set the mblnAdd variable to True. Then the routine clears the current text in the text boxes. It also enables the text boxes by calling ActiveEditing. 6. Private Sub btnAdd_Click(ByVal sender As System.Object, 7. ByVal e As System.EventArgs) Handles btnAdd.Click 8. 9. Dim oCtl As Object 10. Dim strName 11. 12. mblnAdd = True 13. 14. ' Clear the fields 15. For Each oCtl In Me.Controls 16. 17. If TypeOf oCtl Is TextBox And oCtl.name <> "txtCustLimit" Then 18. 19. strName = Mid(oCtl.Name, 4) 20. 21. ' By trapping the exception this way, errors are ignored. 22. Try 23. oCtl.text = "" 24. Catch oexp As Exception 25. End Try 26. 27. End If 28. 29. Next 30. 31. ActivateEditing(True) 32. 33. End Sub 34. Replace the SaveRecord routine with the following code in the form that you created for this How-To. The first change is to add the lines of code that test mblnAdd; if they're True, call the NewRow method off the dataset's Tables collection, specifying the Customers table. The DataRow returned is assigned to mdrCustIndiv. You can then enter the other changes wherever the blnAdd variable is queried. 35. Private Sub SaveRecord() 36. 37. Dim oCtl As Object 38. Dim strName As String 39. 40. If mblnAdd Then 41. mdrCustIndiv = mdsCustIndiv.Tables("Customers").NewRow 42. End If 43. 44. ' Start the editing in the datarow. 45. mdrCustIndiv.BeginEdit() 46. 47. ' Run through the text boxes on the form, and 48. ' if they match up with a field from the record, 49. ' place the value back in the record. 50. For Each oCtl In Me.Controls 51. 52. If TypeOf oCtl Is TextBox Then 53. 54. strName = Mid(oCtl.Name, 4) 55. 56. ' By trapping the exception this way, errors are ignored. 57. Try 58. mdrCustIndiv(strName) = oCtl.text 59. Catch oexp As Exception 60. End Try 61. 62. End If 63. 64. Next 65. 66. ' Finish the editing of the datarow 67. mdrCustIndiv.EndEdit() 68. 69. Try 70. 71. If mblnAdd Then 72. mdsCustIndiv.Tables("Customers").Rows.Add(mdrCustIndiv) 73. End If 74. 75. ' Create an instance of the command builder 76. Dim ocbCustIndiv As OleDb.OleDbCommandBuilder 77. ocbCustIndiv = New OleDb.OleDbCommandBuilder(modaCustIndiv) 78. 79. If mblnAdd Then 80. ' Have the command builder create an Insert SQL command 81. modaCustIndiv.InsertCommand = ocbCustIndiv.GetInsertCommand 82. Else 83. ' Have the command builder create an update SQL command 84. modaCustIndiv.UpdateCommand = ocbCustIndiv.GetUpdateCommand 85. End If 86. 87. ' Perform the specified SQL command; then close the connection 88. modaCustIndiv.Update(mdsCustIndiv, "Customers") 89. mdsCustIndiv.Tables("Customers").AcceptChanges() 90. 91. ' Close the connection 92. If mblnAdd Then 93. modaCustIndiv.InsertCommand.Connection.Close() 94. LoadList() 95. Else 96. modaCustIndiv.UpdateCommand.Connection.Close() 97. End If 98. 99. Catch excData As Exception 100. MessageBox.Show("Error Occurred: " & excData.Message) 101. End Try 102. 103. End Sub 104. Enter the following code to the Click event btnCancel. 105. Private Sub btnCancel_Click(ByVal sender As System.Object, _ 106. ByVal e As System.EventArgs) Handles btnCancel.Click 107. 108. ' Cancel the current editing. 109. 110. If mblnAdd Then 111. mblnAdd = False 112. End If 113. 114. LoadIndividual() 115. ActivateEditing(False) 116. 117. End Sub 118. Enter the following code to the Click event btnDelete. Follow the comments to see what is happening. 119. Private Sub btnDelete_Click(ByVal sender As System.Object, 120. ByVal e As System.EventArgs) Handles btnDelete.Click 121. 122. Dim ocbCustIndiv As OleDb.OleDbCommandBuilder 123. 124. Try 125. 126. ' Delete the record from the datarow object 127. mdrCustIndiv.Delete() 128. 129. ' Instantiate the command builder 130. ocbCustIndiv = New OleDb.OleDbCommandBuilder(modaCustIndiv) 131. 132. ' Have the command builder create a Delete SQL command 133. modaCustIndiv.DeleteCommand = ocbCustIndiv.GetDeleteCommand 134. 135. ' Perform the specified SQL command; then close the connection 136. modaCustIndiv.Update(mdsCustIndiv, "Customers") 137. mdsCustIndiv.Tables("Customers").AcceptChanges() 138. 139. ' Close the connection 140. modaCustIndiv.DeleteCommand.Connection.Close() 141. 142. Catch excData As Exception 143. MessageBox.Show("Error Occurred: " & excData.Message) 144. End Try 145. 146. LoadList() 147. ActivateEditing(False) 148. 149. End Sub How It Works When a user clicks the Add button, the text boxes are all blanked out, and the mblnAdd flag is set as True. Then, after the user adds his information and clicks the Save button, the new record is added back to the server. If the Cancel button is clicked, the individual customer to whom the list is currently pointed is loaded into the text boxes. When the Delete key is pressed, the current record is deleted from the server. Then the customer list is refreshed, and the first customer in the list is displayed in the text boxes. Comments As you can see, adding and deleting a record does not take much more than editing and updating a record using ADO.NET. Using the commands in this How-To and the prior one, you can set it up to handle updating and canceling of multiple records as well. . controls with the dataset to add and delete rows from SQL Server. As with editing and updating data, you need to be able to add and delete rows using the dataset. . 4.2 Add and Delete Rows in a Dataset with ADO. NET Again using the OleDbDataAdapter and OleDbCommandBuilder objects, this How-To