如何在 VisualBasic 中使用 OLEDB 连接选择和存储具有相同 ID 的数据库的多行

Question

    Private Sub GetAffectedTraits(ByVal QuestionIndex)
        NumberOfTraitsAffected = 0
        Dim IndexTracker As Integer

        Dim TraitsAffected(23) As String
        'Set all to Null value
        For i As Integer = 1 To 23
            TraitsAffected(i) = " "
        Next

        Dim Command As New OleDbCommand("SELECT [Affected Trait] FROM Sheet1 WHERE QuestionIndex=" & QuestionIndex & "", TraitValuesConn)
        DB_Reader = Command.ExecuteReader
        While DB_Reader.Read()
            TraitsAffected(IndexTracker) = DB_Reader("Affected Trait")
            IndexTracker += 1
        End While

        For i As Integer = 1 To 23
            MsgBox(TraitsAffected(i)) 'Does not include affected traits yet for some reason
        Next
    End Sub

在这段代码中，我试图从使用相同 ID（或 QuestionIndex）存储的数据库中选择并存储每个“受影响的特征”。我希望它们单独存储在 TraitsAffected 数组中。这是我目前正在尝试的，但它根本没有改变数组。我想坚持我一直在使用 OLEDB 连接的语法。

这是一份学术作业。

Answer 1

如果您不确定受影响特征的数量，最好使用 List 而不是 Array。

检查以下代码，看看它是否适合您。

Private Sub GetAffectedTraits(ByVal QuestionIndex)
    Dim NumberOfTraitsAffected = 0
    Dim TraitsAffected As List(Of String) = New List(Of String)

    Using TraitValuesConn As OleDbConnection = New OleDbConnection("your connection string")
        TraitValuesConn.Open()

        Dim Command As New OleDbCommand("SELECT [Affected Trait] FROM Sheet1 WHERE QuestionIndex=" & QuestionIndex & "", TraitValuesConn)
        Dim DB_Reader = Command.ExecuteReader
        While DB_Reader.Read()
            TraitsAffected.Add(DB_Reader("Affected Trait"))
        End While
    End Using

    For Each value As String In TraitsAffected
        MsgBox(value)
    Next
End Sub