Question

从表中读取数据时，我的一个数值返回-1，而不是用户给出的值。

Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
    Try
        Dim conn As New MySqlConnection("server=localhost;user=root;database=new_project;port=3306;password=********;")
        conn.Open()
        Dim command As New MySqlCommand("SELECT * FROM students;", conn)
        Dim dataSet As New DataSet()
        Dim dataAdapter As New MySqlDataAdapter()
        dataAdapter.SelectCommand = command
        dataAdapter.Fill(dataSet, "students")
        Dim dataTable As DataTable = dataSet.Tables("students")
        For x As Integer = 0 To dataTable.Rows.Count - 1
            Dim newStudent As New Student
            newStudent.intIDNum = dataTable.Rows(x).Item("idNumber")
            newStudent.strFirstName = dataTable.Rows(x).Item("firstName")
            newStudent.strLastName = dataTable.Rows(x).Item("lastName")
            newStudent.chrGender = dataTable.Rows(x).Item("gender")
            newStudent.dateDOB = dataTable.Rows(x).Item("dateOfBirth")
            newStudent.intAge = CInt(Today.Year - newStudent.dateDOB.Year)
            newStudent.intYearGroup = dataTable.Rows(x).Item("yearGroup")
            newStudent.intSkillLevel = dataTable.Rows(x).Item("skillLevel")
            studentList.Add(newStudent)
            lstStudents.Items.Add(newStudent.nameConcat(newStudent.strFirstName, newStudent.strLastName))
        Next
        conn.Close()
    Catch ex As Exception
        MsgBox("Error: " & ex.ToString())
    End Try
End Sub

当读取值＆＃34; skillLevel＆＃34;时，它应该在1和4之间读取，但它读取-1。通过MySQL直接添加到数据库的任何数据都没有发生这种情况，但是在我的程序中使用该方法时，似乎出现了这个问题。

Dim newStudent As New Student
        newStudent.strFirstName = txtForename.Text
        newStudent.strLastName = txtSurname.Text
        newStudent.dateDOB = dtpStudentDOB.Value
        If rdbMale.Checked = True Then
            newStudent.chrGender = "M"
        Else
            newStudent.chrGender = "F"
        End If
        newStudent.intAge = newStudent.calcAge(dtpStudentDOB.Value)
        newStudent.intSkillLevel = cmbSkillLevel.SelectedItem
        newStudent.intYearGroup = cmbYearGroup.SelectedItem
        newStudent.intIDNum = CInt(txtStudentID.Text)
        Dim conn As New MySqlConnection("server=localhost;user=root;database=new_project;port=3306;password=********;")
        Try
            conn.Open()
            Dim command As MySqlCommand = New MySqlCommand
            command.Connection = conn
            command.CommandText = "INSERT INTO Students VALUES(@IdNumber, @firstName, @lastName, @gender, @dateOfBirth, @yearGroup, @skillLevel);"
            command.Prepare()
            command.Parameters.AddWithValue("@IdNumber", newStudent.intIDNum)
            command.Parameters.AddWithValue("@firstName", newStudent.strFirstName)
            command.Parameters.AddWithValue("@lastName", newStudent.strLastName)
            command.Parameters.AddWithValue("@gender", newStudent.chrGender)
            command.Parameters.AddWithValue("@dateOfBirth", newStudent.dateDOB)
            command.Parameters.AddWithValue("@yearGroup", newStudent.intYearGroup)
            command.Parameters.AddWithValue("@skillLevel", newStudent.intSkillLevel)
            command.ExecuteNonQuery()
        Catch ex As Exception
            MsgBox("Error: " & ex.ToString())
        Finally
            conn.Close()
        End Try

这是将学生添加到系统的代码部分。究竟是什么原因导致出现此错误？

作为参考，我在数据中添加的主要表单使用枚举：

Private Enum SkillLevels As Integer
    One = 1
    Two = 2
    Three = 3
    Four = 4
End Enum

然后我将其链接到下拉列表：cmbSkillLevel.DataSource = System.Enum.GetValues(GetType(SkillLevels))

Answer 1

显而易见的可能是在SKILL-LEVEL下拉列表中没有选择，这就是为什么你得到-1，你可以通过确保它不是-1来检查是否在下拉列表中做出选择

例如，你的技能下降可能看起来像这样

<select id="SkillLevel">
  <option value="0" selected="selected">Please Select</option>
  <option value="1">Low</option>
  <option value="2">Medium</option>
  <option value="3">High</option>
  <option value="4">Very-High</option>
</select>

如果没有选择，返回的默认值将为零（0）并且您可以通过查找返回值来检查有效值＆gt; 0

据我所知，如果省略selected =“selected”，则返回值为-1

Answer 2

我想我错误地解释了@ tolanj的评论。看来，在加载我的数据时，系统无法读取我的skillLevel列。为了解决这个问题，我将newStudent.intSkillLevel = row.Item("skillLevel")更改为newStudent.intSkillLevel = SByte.Parse(row.Item("skillLevel"))。

从我的数据库中检索数据时出现奇怪的问题

2 个答案: