在select statment中返回一行数据

问题描述

我正在开发一个学生指纹注册系统。我正在使用带有onetouch sdk的数字角色u.r.u4500。到目前为止，我已经能够将指纹保存到mysql中并完成验证。我现在所困的是如何在验证指纹时从数据库中检索studentID。验证完成后出现此错误



System.Data.dll中发生类型'System.IndexOutOfRangeException'的异常，但未在用户代码中处理其他信息：位置0没有行。此行发生错误



我尝试过：



我能够执行验证。

I'm developing a student fingerprint registration system in vb. I'm using the digital persona u.r.u4500 with the onetouch sdk. I have so far been able to save the fingerprint into mysql and done verification also. What l'm stuck now is how to retrieve the studentID from the database when the fingerprint is verified. This error comes up after verification is complete

An exception of type 'System.IndexOutOfRangeException' occurred in System.Data.dll but was not handled in user code Additional information: There is no row at position 0. The error occurs on this line

What I have tried:

As l am able to perform verification.

Private Sub verifyControl_OnComplete(ByVal Control As Object, ByVal FeatureSet As DPFP.FeatureSet, ByRef EventHandlerStatus As DPFP.Gui.EventHandlerStatus) Handles verifyControl.OnComplete

        Try

        cn.Open()
        sqlCommand.CommandText = "Select * from student"
        sqlCommand.CommandType = CommandType.Text
        sqlCommand.Connection = cn
        Dim lrd As MySqlDataReader = sqlCommand.ExecuteReader()

        While lrd.Read()
            usr = lrd("print")

        End While
        lrd.Dispose()
        bytes = Nothing
        bytes = usr
        template = New DPFP.Template()
        template.DeSerialize(usr)
        'Perform match
        matcher.Verify(FeatureSet, template, matchResult)
        If matchResult.Verified Then
            EventHandlerStatus = Gui.EventHandlerStatus.Success

            MessageBox.Show("Verified!, Fingerprint exist in database")
I suspect the fault to be from this block

            sqlCommand.CommandText = " select StudentID from student  where
            print like '%template%' "

            Dim publictable As New DataTable
            Try

                adapter.SelectCommand = sqlCommand

                adapter.Fill(publictable)
                txtstudentID.Text = publictable.Rows(0).Item(1)
            Finally


                adapter.Dispose()
                cn.Close()
            End Try

我传递的变量到一个mysql语句。现在变量驻留在代码而不是数据库中，因此查询它将不会返回我当前获得的结果。有没有办法使用select语句查询mysql来检索与数据库中的指纹模板相关联的studentID（BLOB）。

I am passing a variable to an mysql statement. Now the variable resides in the code and not the database so querying it will return no results which l am currently getting. Is there a way to use select statement to query mysql to retrieve the studentID associated with the fingerprint template in the database(BLOB).

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