我正在尝试将从 SQL 查询检索到的数据写入 Visual Basic 2012 中的文本文件中。这是一些代码 - 我只需要朝正确的方向推动:
Imports System.Data.SqlClient
Imports System.IO
Public Class frmResults
Dim cn As New SqlConnection("Data Source=(LocalDB)\v11.0;AttachDbFilename=C:\Users\bryan\Documents\TeamGFinalProject\BookCollection.MDF;Integrated Security=True;Connect Timeout=30")
Dim cmd As New SqlCommand
Dim dr As SqlDataReader
Dim table As New DataTable("sales")
Private Sub frmResults_Load(sender As Object, e As EventArgs) Handles MyBase.Load
cmd.Connection = cn
End Sub
Private Sub BtnReport_Click(sender As Object, e As EventArgs) Handles BtnReport.Click
cn.Open()
cmd.CommandText = "select * from sales where ord_date BETWEEN '" & dtpStart.Text & "' AND '" & dtpEnd.Text & "' Order BY ord_date;"
Using sw As StreamWriter = New StreamWriter("Dates.txt")
Dim reader As SqlDataReader = cmd.ExecuteReader()
sw.WriteLine(reader)
reader.Close()
End Using
cn.Close()
End Sub
End Class
从 SqlDataReader 读取时,您需要读取一行结果 (SqlDataReader.Read),对其执行某些操作,然后继续处理下一条记录,直到获得所需的内容。您可以使用 SqlDataReader.GetValues 方法一次性获取行中的所有列值。
建议:使用参数来构建命令文本(参见此处)。
Private Sub BtnReport_Click(sender As Object, e As EventArgs) Handles BtnReport.Click
cn.Open()
cmd.CommandText = "select * from sales where ord_date BETWEEN '" & dtpStart.Text & "' AND '" & dtpEnd.Text & "' Order BY ord_date;"
Using sw As StreamWriter = New StreamWriter("Dates.txt")
Using reader As SqlDataReader = cmd.ExecuteReader()
Dim values(reader.FieldCount - 1) As Object
While reader.Read
reader.GetValues(values)
sw.WriteLine(String.Join(vbTab, values))
End While
End Using
End Using
cn.Close()
你们非常接近。
SqlDataReader 对象有点类似于 StreamReader 或其他读取器对象。您需要做的实际上是使用读取器对象迭代数据。当您阅读时,这些字段将填充到阅读器对象中。然后您可以将该数据写出。这是一个简单的工作示例:
While (reader.Read)
'Get data row by row
Dim row_data(reader.FieldCount - 1) As String
Dim i As Integer
For i = 0 To reader.FieldCount - 1
row_data(i) = reader(i).ToString
Next
'Build a single string (simplistic CSV style)
String.Join(",",row_data)
'Write to file
sw.WriteLine(reader)
End While
这可能不是处理此问题的最有效方法,但它应该可以让您很好地了解正在发生的情况。