【发布时间】：2015-04-24 22:19:47
【问题描述】：
我知道这个主题有很多，但我似乎无法获取这些信息并将其自定义到我的代码中。 我在保存数据时遇到问题，因此当我关闭程序并再次打开时数据仍然存在。这是一个简单的程序，其中数据通过文本框输入到数据网格视图中。起初什么都没有发生，但经过数小时的代码工作后，我开始在 dataAdapter.Update(dt) 行上收到此错误消息：
不支持对多个基表进行动态 SQL 生成。
我知道我的代码没有遵循最佳实践规则，但我对编程很陌生，所以玩得开心。在此先感谢您，我真的很感谢您的帮助。
这是我的代码：
Public Class frmGradeBook
'data grid view for recording students grades
Dim connStr As String = "Provider=Microsoft.ACE.OLEDB.12.0;" & _
"Data Source=GRADEBOOK.accdb"
Dim sqlStr As String = "SELECT firstName,lastName,firstExam,secondExam,finalExam " & _
"FROM Students INNER JOIN Grades ON Students.studentID = Grades.studentID "
Dim dataAdapter As New OleDb.OleDbDataAdapter(sqlStr, connStr)
Dim dt As New DataTable()
'secondary data grid view for displaying students grade
Dim connStr1 As String = "Provider=Microsoft.ACE.OLEDB.12.0;" & _
"Data Source=GRADEBOOK.accdb"
Dim sqlStr1 As String = "SELECT firstName, lastName, finalExam FROM Students INNER JOIN Grades ON Students.studentID = Grades.studentID "
Dim dataAdapter1 As New OleDb.OleDbDataAdapter(sqlStr1, connStr1)
Dim dt1 As New DataTable()
Private Sub frmGradeBook_Load(sender As Object, e As EventArgs) Handles MyBase.Load
dataAdapter.Fill(dt)
dgvRecordGrades.DataSource = dt
dataAdapter1.Fill(dt1)
dgvDisplayGrades.DataSource = dt1
dgvDisplayGrades.Visible = False
lstGrade.Visible = False
End Sub
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles btnRecord.Click
dgvDisplayGrades.Visible = False
dgvRecordGrades.Visible = True
lstGrade.Visible = False
'validates the data
Dim studentID As String = txtID.Text.ToUpper
Dim row As Integer
Dim dataGridRow As DataGridViewRow = dgvRecordGrades.Rows(1)
If IsNumeric(txtFirstExam.Text) And IsNumeric(txtSecExam.Text) And IsNumeric(txtFinalExam.Text) Then
If (txtFirstExam.Text).ToString().IndexOf(".") = -1 Then
Dim firstExam As Double = CDbl(txtFirstExam.Text)
Dim secondExam As Double = CDbl(txtSecExam.Text)
Dim finalExam As Double = CDbl(txtFinalExam.Text)
If firstExam <= 100 And secondExam <= 100 And finalExam <= 100 Then
If firstExam >= 0 And secondExam >= 0 And finalExam >= 0 Then
If studentID = "AJ-123456" Then
row = 0
ElseIf studentID = "FA-192837" Then
row = 1
ElseIf studentID = "GG-567876" Then
row = 2
ElseIf studentID = "GJ-987654" Then
row = 3
ElseIf studentID = "LS-222333" Then
row = 4
Else
MessageBox.Show("The student ID provided is not valid. Please try again.")
End If
'records the grades
dgvRecordGrades.Item(2, row).Value = firstExam
dgvRecordGrades.Item(3, row).Value = secondExam
dgvRecordGrades.Item(4, row).Value = finalExam
Else
MessageBox.Show("Invalid input. Please try again")
End If
Else
MessageBox.Show("Invalid input. Please try again")
End If
Else
MessageBox.Show("Please enter whole numbers. Try again.")
End If
Else
MessageBox.Show("Invalid input. Please try again")
End If
End Sub
Private Sub Button1_Click_2(sender As Object, e As EventArgs) Handles btnPostable.Click
dgvRecordGrades.Visible = False
dgvDisplayGrades.Visible = False
lstGrade.Visible = True
lstGrade.Items.Clear()
If Not IsDBNull((dgvDisplayGrades.Item(2, 0).Value)) Then
lstGrade.Items.Add("3456 " & LetterGrade(CDbl(dgvDisplayGrades.Item(2, 0).Value)))
Else
lstGrade.Items.Add("3456 NO GRADE AVAILABLE")
End If
If Not IsDBNull((dgvDisplayGrades.Item(2, 1).Value)) Then
lstGrade.Items.Add("2837 " & LetterGrade(CDbl(dgvDisplayGrades.Item(2, 1).Value)))
Else
lstGrade.Items.Add("2837 NO GRADE AVAILABLE")
End If
If Not IsDBNull((dgvDisplayGrades.Item(2, 2).Value)) Then
lstGrade.Items.Add("7876 " & LetterGrade(CDbl(dgvDisplayGrades.Item(2, 2).Value)))
Else
lstGrade.Items.Add("7876 NO GRADE AVAILABLE")
End If
If Not IsDBNull((dgvDisplayGrades.Item(2, 3).Value)) Then
lstGrade.Items.Add("7654 " & LetterGrade(CDbl(dgvDisplayGrades.Item(2, 3).Value)))
Else
lstGrade.Items.Add("7654 NO GRADE AVAILABLE")
End If
If Not IsDBNull((dgvDisplayGrades.Item(2, 4).Value)) Then
lstGrade.Items.Add("2333 " & LetterGrade(CDbl(dgvDisplayGrades.Item(2, 4).Value)))
Else
lstGrade.Items.Add("2333 NO GRADE AVAILABLE")
End If
End Sub
Private Sub Button1_Click_1(sender As Object, e As EventArgs) Handles btnDisplay.Click
dgvDisplayGrades.Visible = True
dgvRecordGrades.Visible = False
lstGrade.Visible = False
For col As Integer = 2 To 2
For row As Integer = 0 To 4
If Not IsDBNull(dgvRecordGrades.Item(col, row).Value) Then
Dim firstExam As Double = CDbl(dgvRecordGrades.Item(2, row).Value)
Dim secExam As Double = CDbl(dgvRecordGrades.Item(3, row).Value)
Dim finalExam As Double = CDbl(dgvRecordGrades.Item(4, row).Value)
dgvDisplayGrades.Item(2, row).Value = SemAvg(firstExam, secExam, finalExam)
Else
End If
Next
Next
End Sub
Function SemAvg(firstMid As Double, secondMid As Double, final As Double) As Double
Dim semAverage As Double
semAverage = (firstMid + secondMid + (2 * final)) / 4
Math.Round(semAverage)
Return semAverage
End Function
Function LetterGrade(semAvg As Double) As String
Select Case semAvg
Case Is >= 90
Return "A"
Case Is >= 80
Return "B"
Case Is >= 70
Return "C"
Case Is >= 60
Return "D"
Case Else
Return "F"
End Select
End Function
Private Sub btnSave_Click(sender As Object, e As EventArgs) Handles btnSave.Click
Dim changes As Integer
Dim commandBuilder As New _
OleDb.OleDbCommandBuilder(dataAdapter)
changes = dataAdapter.Update(dt)
If changes > 0 Then
MessageBox.Show(changes & " changed rows.")
Else
MessageBox.Show("No changes made.")
End If
End Sub
Private Sub frmGradeBook_FormClosing(sender As Object, e As FormClosingEventArgs) Handles MyBase.FormClosing
dataAdapter.Dispose()
dataAdapter1.Dispose()
End Sub
End Class
【问题讨论】：
标签： database vb.net datagridview save