Tài liệu Edit Data and Update Changes That Are Made to an ADO.NET pdf

How do you edit and update data using the DataSet object?. DataAdapter, DataSet, DataTable, and DataRow Properties and Methods Object /Method Property Description DataAdapter Fill Fills

4.1 Edit Data and Update Changes That Are Made to an ADO.NET DataSet Object

Listing and viewing data is easy What you really need to do is to be able to edit and update data You know you can use the DataSet object and some of its objects and

methods to perform this task How do you edit and update data using the DataSet object?

Technique

In this How-To, you will use the DataAdapter, DataSet, DataTable, and DataRow

objects You have experienced some of the properties and methods of each of these objects before In this chapter, you are going to be using the following properties and methods that are shown in Table 4.1

Table 4.1 DataAdapter, DataSet, DataTable, and DataRow Properties and Methods Object /Method Property Description

DataAdapter Fill Fills DataSet and DataTable objects

CommandBuilde

r

GetUpdateComman

d

Creates an Update command and places it into the data adapter's UpdateCommand property DataAdapter UpdateCommand Holds the SQL statement for the update DataAdapter Close Closes the connection off the

UpdateCommand The syntax is dataadapter.UpdateCommand.Connect.Close()

DataAdapter Update Performs the update command against the

dataset

DataSet Tables Represents a collection of tables found within

a dataset

DataSet Rows Contains a collection of rows within a

specified table in a dataset

DataSet AcceptChanges Sends the changes back to the server

DataRow ToString Retrieves the data from the column that is

specified in the DataRow and returns it as a string value

DataRow BeginEdit Begins the editing of a DataRow, allowing

you to replace values in the columns

DataRow EndEdit Completes the editing of a DataRow

You will see these objects with their properties and methods used in the following steps

Steps

Open and run the VB.NET-Chapter 4 solution From the main form, click on the

command button with the caption How-To 4.1 When the form loads, click on the Load List button to display the customers that begin with the letter A Click the Edit button You will notice that the fields have now taken on a sunken look Place the cursor into the City field and change the value to Dunkirk Now click Save If you move off the record and move back on, you will notice that the value has been saved

This form looks similar to the form created in Chapter 1 The difference is that this time you will not be using controls that are bound at design time You can see the form in Figure 4.1

1 Create a new Windows Form

2 Add the following controls, setting the properties as listed in Table 4.2

Table 4.2 Controls Property Settings Object Property Setting

Label Name

Caption

Label1 Customer TextBox Name

Text

txtCustLimit

A Button Name

Caption

btnLoadList Load List ListBox Name lstCustomers Label Caption Customer ID Label Caption Company Name Label Caption Contact

Label Caption Contact Title

Label Caption Address Label Caption City Label Caption Region Label Caption Country Label Caption Phone Label Caption Fax TextBox Name txtCustomerID TextBox Name txtCompanyName TextBox Name txtContact TextBox Name txtContactTitle TextBox Name txtAddress TextBox Name txtCity TextBox Name txtRegion TextBox Name txtPostalCode TextBox Name txtCountry TextBox Name txtPhone TextBox Name txtFax Button Name

Caption

btnEdit

&Edit Button Name

Caption

btnSave

&Save Button Name

Caption

btnCancel

&Cancel

3 Note

Notice that the Text property of the text boxes is not being set at design time In Chapter 1, "Developing Windows Forms Using Bound Controls," they were set to columns of a dataset that was included on the form In this How-To, they will be set at run-time

4 In the class module for the form, add the following three Private declarations just below the line of code that reads Windows Form Designer generated code These three objects will be used throughout the form

5 Dim mdsCustIndiv As New DataSet()

6 Dim modaCustIndiv As OleDb.OleDbDataAdapter

7 Dim mdrCustIndiv As DataRow

8 Enter the following code as the Click event for btnLoadList:

9 Private Sub btnLoadList_Click(ByVal sender As System.Object, _

10 ByVal e As System.EventArgs) Handles btnLoadList.Click

11

12 ' Move the loading of the list to a subroutine for

13 ' additional(calls)

14 LoadList()

15

16 End Sub

17 Create the LoadList routine by entering the following code into the form you created for this How-To This code creates and fills a data table using a data

adapter The string that the data adapter uses creates a Select statement by using the txtCustLimit text box The DataSource, DisplayMember, and ValueMember properties of the list box are then bound Last, the LoadIndividual routine is called, which is described in the next step

18 Private Sub LoadList()

19

20 Dim odaCustList As OleDb.OleDbDataAdapter

21 Dim dtCustList As DataTable = New DataTable()

22

23 Dim strSQL As String

24

25 ' Create the SQL String

26 strSQL = "Select CustomerID, CompanyName " & _

27 From Customers Where CustomerID Like '" & _

28 Me.txtCustLimit.Text & "%'"

29

30

31 ' Set up the exception catch

32 Try

33

34 ' Create an instance of the data adapter; then fill the data

35 table

36 odaCustList = New OleDb.OleDbDataAdapter(strSQL, _

37 BuildCnnStr("(local)", "Northwind"))

38 odaCustList.Fill(dtCustList)

39

40 ' Bind the data to the list box

41 lstCustomers.DataSource = dtCustList

42 lstCustomers.DisplayMember = "CompanyName"

43 lstCustomers.ValueMember = "CustomerID"

44

45 LoadIndividual()

46 Catch oexpData As OleDb.OleDbException

47 MsgBox(oexpData.Message)

48 End Try

49

50 End Sub

51 Create the LoadIndividual routine by entering the following code in the form you created for this How-To Taking the SelectedItem from the list box, a data adapter

is created, and a dataset is filled Next, the individual DataRow is created Last, each of the TextBox controls is loaded with the value from the column with the corresponding name Notice the use of the Try-Catch-End-Try to ignore controls that don't have a like column in the DataRow

52 Private Sub LoadIndividual()

53

54 Dim strSQL As String

55 Dim strName As String

56 Dim oCtl As Object

57

58 mdsCustIndiv.Clear()

59

60 If Me.lstCustomers.SelectedIndex <> -1 Then

61

62 Try

63 ' Load the individual record into the dataset

64 strSQL = "Select * from Customers Where CustomerID = '" &

65 Me.lstCustomers.SelectedItem(0) & "'"

66 modaCustIndiv = New OleDb.OleDbDataAdapter(strSQL, _

67 BuildCnnStr("(local)", "Northwind"))

68

69 ' Fill the dataset

70 modaCustIndiv.Fill(mdsCustIndiv, "Customers")

71

72 ' Grab the individual data row

73 mdrCustIndiv = mdsCustIndiv.Tables("Customers").Rows(0)

74

75 Catch oexpData As OleDb.OleDbException

76

77 MessageBox.Show("Error loading individual data: " _

78 & oexpData.Message)

79 Exit Sub

80

81 End Try

82

83 ' Run through the text boxes on the form, and

84 ' if they match up with a field from the record,

85 ' load them

86

87 For Each oCtl In Me.Controls

88

89 If TypeOf oCtl Is TextBox Then

90

91 strName = Mid(oCtl.Name, 4)

92

93 ' By trapping the exception this way, errors are ignored

94 Try

95 oCtl.text = mdrCustIndiv(strName).ToString

96 Catch oexp As Exception

97 End Try

98

99 End If

100

101 Next

102

103 End If

104 End Sub

105 Enter the following code to the Click event for lstCustomers:

106 Private Sub lstCustomers_Click(ByVal sender As Object,

107 ByVal e As System.EventArgs) Handles lstCustomers.Click

108

109 ' Fill the current list item's individual dataset

110 LoadIndividual()

111

112 End Sub

113 Enter the following code to the Click event for btnEdit:

114 Private Sub btnEdit_Click(ByVal sender As System.Object,

115 ByVal e As System.EventArgs) Handles btnEdit.Click

116

117 ' Enable the editing of the form

118 ActivateEditing(True)

119

120 End Sub

121 Create the ActivateEditing routine by entering the following code in the form you created for this How-To Introduced in Chapter 1, this code goes through each of controls on the form, looking for text boxes, then setting the BorderStyle and BackColor properties based on whether the controls are to be enabled or disabled The Enabled property of each control is then set as well

122 Private Sub ActivateEditing(ByVal bEnable As Boolean)

123

124

125 Dim oCurr As Object

126

127 ' Loop through each of the controls on the form

128 For Each oCurr In Me.Controls()

129

130 ' Check to see if the control is a text box

131 If TypeOf oCurr Is TextBox And oCurr.Name <> "txtCustLimit" Then

132

133 ' If so, toggle the properties

134 If bEnable Then

135

136 oCurr.BorderStyle() = _

137 System.Windows.Forms.BorderStyle.Fixed3D

138

139 oCurr.BackColor() = System.Drawing.Color.White

140

141 Else

142

143 oCurr.BorderStyle() = _

144 System.Windows.Forms.BorderStyle.FixedSingle

145

146 oCurr.BackColor() = Me.BackColor

147

148

149 End If

150

151 oCurr.Enabled = bEnable

152

153 End If

154 Next

155

156 End Sub

157 Enter the following code to the Click event btnSave:

158 Private Sub btnSave_Click(ByVal sender As System.Object, _

159 ByVal e As System.EventArgs) Handles btnSave.Click

160

161 ' Save the information

162 SaveRecord()

163

164 ' Disable the text boxes

165 ActivateEditing(False)

166

167 End Sub

168 Create the SaveRecord routine by entering the following code in the form that you created for this How-To Using a DataRow object, the BeginEdit method

is called, and then each of the controls is stored back into the columns of the same names, if they exist The EndEdit method is then called to complete the editing of the DataRow A CommandBuilder object is created to create the Update command for the DataAdapter object The DataAdapter Update method is called to update the dataset with the data changed and then the AcceptChanges of the DataSet object This accepts all the changes for all the objects and posts the data back to the server Finally, the connection is closed for the UpdateCommand of the

DataAdapter object

169 Private Sub SaveRecord()

170

171 Dim oCtl As Object

172 Dim strName As String

173

174 ' Start the editing in the datarow

175 mdrCustIndiv.BeginEdit()

176

177 ' Run through the text boxes on the form, and

178 ' if they match up with a field from the record,

179 ' place the value back in the record

180 For Each oCtl In Me.Controls

181

182 If TypeOf oCtl Is TextBox Then

183

184 strName = Mid(oCtl.Name, 4)

185

186 ' By trapping the exception this way, errors are ignored

187 Try

188 mdrCustIndiv(strName) = oCtl.text

189 Catch oexp As Exception

190 End Try

191

192 End If

193

194 Next

195

196 ' Finish the editing of the data row

197 mdrCustIndiv.EndEdit()

198

199 Try

200

201 ' Create an instance of the command builder

202 Dim ocbCustIndiv As OleDb.OleDbCommandBuilder

203 ocbCustIndiv = New OleDb.OleDbCommandBuilder(modaCustIndiv)

204

205 ' Have the command builder create an update SQL command

206 modaCustIndiv.UpdateCommand = ocbCustIndiv.GetUpdateCommand

207

208 ' Perform the update SQL command; then close the connection

209 modaCustIndiv.Update(mdsCustIndiv, "Customers")

210 mdsCustIndiv.Tables("Customers").AcceptChanges()

211 modaCustIndiv.UpdateCommand.Connection.Close()

212

213

214 Catch excData As Exception

215

216 End Try

217

218 End Sub

219 Enter the following code to the Click event btnCancel:

220 Private Sub btnCancel_Click(ByVal sender As System.Object, _

221 ByVal e As System.EventArgs) Handles btnCancel.Click

222

223 ' Use the BindingContext class to cancel the current editing

224 LoadIndividual()

225 ActivateEditing(False)

226

227 End Sub

Figure 4.1 Although this looks like the form created in Chapter 1, you have more

control over this version with unbound controls

How It Works

When the user clicks on the btnLoadList Button, the lstCustomers list box is loaded via the odaCustList data adapter and dtCustList data table The first customer's information is then loaded in the text boxes on the right side of the form When the btnEdit button is clicked, the look of the text boxes is changed to sunken, and they are enabled for editing

of the text After changing the data, when the user clicks on the btnSave button, the data

is then stored back into the server, and the text boxes are changed to disabled If the btnCancel is clicked, the text boxes are changed to disabled

Comments

Although it takes a bit more code to handle the editing and updating of data with unbound controls versus bound controls, you might like it better because you can control the code With bound controls, the code is written for you The code that is displayed here can be modified to be more generic so that you don't have to write individual routines for each form