如何停止循环

时间：2015-10-06 15:22:40

标签： vb.net

我有问题直到循环。当记录成功保存并出现消息框后，单击确定按钮后，它只显示消息框并无休止地重复。我不知道代码是什么。请帮忙。

        MySqlConn.Open()
        Dim last, midd, first, age, occu, phone As MySqlDataReader
        Dim cmd1, cmd2, cmd3, cmd4, cmd5, cmd6, cmd7, cmd8, cmd9, cmd10, cmd11 As New MySqlCommand
        Dim query1, query2, query3, query4, query5, query6, query7, query8, query9, query10, query11 As String

        'lastname query
        query1 = "SELECT * FROM newpatient WHERE Lastname ='" & txtLastname.Text & "'"
        cmd1 = New MySqlCommand(query1, MySqlConn)
        last = cmd1.ExecuteReader

        'first query
        query2 = "SELECT * FROM newpatient WHERE Firstname ='" & txtFirstname.Text & "'"
        cmd2 = New MySqlCommand(query2, MySqlConn)
        last.Close()
        first = cmd2.ExecuteReader

        'middle query
        query3 = "SELECT * FROM newpatient WHERE Middlename ='" & txtMiddlename.Text & "'"
        cmd3 = New MySqlCommand(query3, MySqlConn)
        first.Close()
        midd = cmd3.ExecuteReader

        'age query
        query4 = "SELECT * FROM newpatient WHERE Age ='" & txtAge.Text & "'"
        cmd4 = New MySqlCommand(query4, MySqlConn)
        midd.Close()
        age = cmd4.ExecuteReader

        'gender query
        query5 = "SELECT * FROM newpatient WHERE Occupation ='" & txtOccupation.Text & "'"
        cmd5 = New MySqlCommand(query5, MySqlConn)
        age.Close()
        occu = cmd5.ExecuteReader

        'phone query
        query6 = "SELECT * FROM newpatient WHERE Mobile_Number ='" & txtMobileNumber.Text & "'"
        cmd6 = New MySqlCommand(query6, MySqlConn)
        occu.Close()
        phone = cmd6.ExecuteReader


        Do While last.HasRows = 0 And first.HasRows = 0 And midd.HasRows = 0 And occu.HasRows = 0 And phone.HasRows = 0 And age.HasRows = 0

            Dim cmd As MySqlCommand = MySqlConn.CreateCommand
            cmd.CommandText = String.Format("INSERT INTO newpatient (ID, Lastname, Firstname, Middlename, Age, Mobile_Number, Gender, Address, Occupation, Month, Day, Year )" &
                                            "VALUES ('{0}' ,'{1}' ,'{2}' ,'{3}' ,'{4}' ,'{5}' , '{6}', '{7}', '{8}', '{9}', '{10}', '{11}' )",
                                            txtID.Text,
                                            txtLastname.Text,
                                            txtFirstname.Text,
                                            txtMiddlename.Text,
                                            txtAge.Text,
                                            txtMobileNumber.Text,
                                            cmbGender.SelectedItem,
                                            txtAddress.Text,
                                            txtOccupation.Text,
                                            cmbMonth.SelectedItem,
                                            cmbDay.SelectedItem,
                                            cmbYear.SelectedItem)
            phone.Close()
            Dim affectedrows As Integer = cmd.ExecuteNonQuery()
            If affectedrows > 0 Then
                MsgBox("Record successfully saved!", MsgBoxStyle.Information, "Success")

'AUTO GENERATE RANDOM IDs
                Dim random As New Random
                Dim id As Integer
                id = (random.Next(100000000, 1000000000))
                txtID.Text = id
                'CLEARS TEXTBOXES
                txtMobileNumber.Text = ""
                txtLastname.Text = ""
                txtFirstname.Text = ""
                txtMiddlename.Text = ""
                txtAge.Text = 0
                cmbGender.SelectedItem = ""
                cmbDay.SelectedItem = ""
                cmbMonth.SelectedItem = ""
                cmbYear.SelectedItem = 0
                txtAddress.Text = ""
                txtOccupation.Text = ""
                txtLastname.Select()
            Else
                MsgBox("Saving record failed.", MsgBoxStyle.Critical, "Failed")
                'AUTO GENERATE RANDOM IDs
                Dim random As New Random
                Dim id As Integer
                id = (random.Next(100000000, 1000000000))
                txtID.Text = id
                'CLEARS TEXTBOXES
                txtMobileNumber.Text = ""
                txtLastname.Text = ""
                txtFirstname.Text = ""
                txtMiddlename.Text = ""
                txtAge.Text = 0
                cmbGender.SelectedItem = ""
                cmbDay.SelectedItem = ""
                cmbMonth.SelectedItem = ""
                cmbYear.SelectedItem = 0
                txtAddress.Text = ""
                txtOccupation.Text = ""
                txtLastname.Select()
            End If
        Loop
        'CLEARS TEXTBOXES
        txtMobileNumber.Text = ""
        txtLastname.Text = ""
        txtFirstname.Text = ""
        txtMiddlename.Text = ""
        txtAge.Text = 0
        cmbGender.SelectedItem = ""
        cmbDay.SelectedItem = ""
        cmbMonth.SelectedItem = ""
        cmbYear.SelectedItem = 0
        txtAddress.Text = ""
        txtOccupation.Text = ""
        MsgBox("Patient has already registered!", MsgBoxStyle.Critical, "Already registered")

        MySqlConn.close()

1 个答案:

答案 0 :(得分：1)

要停止循环，需要调用Exit，如下所示：

Exit Do

话虽如此，你不应该只是在不要求满足条件的情况下调用Exit，否则你会遇到意想不到的行为。

但是你在这里遇到了更大的问题。我将快速列出它们并包含一个快速的伪代码建议（因为我从未在.Net中使用MySql，因此根本不熟悉API，所以这段代码需要在它工作之前进行修改）

Dim cmd As MySqlCommand = MySqlConn.CreateCommand
cmd.CommandText = "INSERT INTO newpatient (ID, Lastname, Firstname, Middlename, Age, Mobile_Number, Gender, Address, Occupation, Month, Day, Year )" &
                    "VALUES (:ID, :Lastname, :Firstname, :Middlename, :Age, :Mobile_Number, :Gender, :Address, :Occupation, :Month, :Day, :Year)"
cmd.Parameters.Add(new MySqlParameter(":ID", txtID.Text))
cmd.Parameters.Add(new MySqlParameter(":Lastname", txtLastname.Text))
cmd.Parameters.Add(new MySqlParameter(":Firstname", txtFirstname.Text))
cmd.Parameters.Add(new MySqlParameter(":Middlename", txtMiddlename.Text))
cmd.Parameters.Add(new MySqlParameter(":Age", txtAge.Text))
cmd.Parameters.Add(new MySqlParameter(":Mobile_Number", txtMobileNumber.Text))
cmd.Parameters.Add(new MySqlParameter(":Gender", cmbGender.SelectedItem))
cmd.Parameters.Add(new MySqlParameter(":Address", txtAddress.Text))
cmd.Parameters.Add(new MySqlParameter(":Occupation", txtOccupation.Text))
cmd.Parameters.Add(new MySqlParameter(":Month", cmbMonth.SelectedItem))
cmd.Parameters.Add(new MySqlParameter(":Day", cmbDay.SelectedItem))
cmd.Parameters.Add(new MySqlParameter(":Year", cmbYear.SelectedItem))

Dim affectedrows As Integer = cmd.ExecuteNonQuery()
If affectedrows = 1 Then
    MsgBox("Record successfully saved!", MsgBoxStyle.Information, "Success")
Else
    If affectedrows = 0 Then
        'Most likely the record already existed, call an update here and if you get 1 result, the record existed and you just saved changes
        MsgBox("Patient has already registered!", MsgBoxStyle.Critical, "Already registered")
        'You could change the above to a Yes/No question about updating the record and have the result in an if to update the record at the user's discretion.
        cmd = MySqlConn.CreateCommand
        cmd.CommandText = "UPDATE newpatient " &
                            "SET Lastname = :Lastname, Firstname = :Firstname, Middlename = :Middlename, Age = :Age, Mobile_Number = :Mobile_Number, " &
                            "     Gender = :Gender, Address = :Address, Occupation = :Occupation, Month = :Month, Day = :Day, Year = :Year " &
                            "WHERE ID = :ID"
        cmd.Parameters.Add(new MySqlParameter(":ID", txtID.Text))
        cmd.Parameters.Add(new MySqlParameter(":Lastname", txtLastname.Text))
        cmd.Parameters.Add(new MySqlParameter(":Firstname", txtFirstname.Text))
        cmd.Parameters.Add(new MySqlParameter(":Middlename", txtMiddlename.Text))
        cmd.Parameters.Add(new MySqlParameter(":Age", txtAge.Text))
        cmd.Parameters.Add(new MySqlParameter(":Mobile_Number", txtMobileNumber.Text))
        cmd.Parameters.Add(new MySqlParameter(":Gender", cmbGender.SelectedItem))
        cmd.Parameters.Add(new MySqlParameter(":Address", txtAddress.Text))
        cmd.Parameters.Add(new MySqlParameter(":Occupation", txtOccupation.Text))
        cmd.Parameters.Add(new MySqlParameter(":Month", cmbMonth.SelectedItem))
        cmd.Parameters.Add(new MySqlParameter(":Day", cmbDay.SelectedItem))
        cmd.Parameters.Add(new MySqlParameter(":Year", cmbYear.SelectedItem))
        affectedrows = cmd.ExecuteNonQuery()
        If affectedrows = 1 Then
            MsgBox("Record successfully saved!", MsgBoxStyle.Information, "Success")
        Else
            MsgBox("Saving record failed.", MsgBoxStyle.Critical, "Failed")
        End If
    Else
        'Should never get here.  We covered 0 and 1 in the other two logic branches.
        'In this small demo, handling when more than 1 record gets updated is out of scope. 
    End If                
End If


'CLEARS TEXTBOXES
txtMobileNumber.Text = ""
txtLastname.Text = ""
txtFirstname.Text = ""
txtMiddlename.Text = ""
txtAge.Text = 0
cmbGender.SelectedItem = ""
cmbDay.SelectedItem = ""
cmbMonth.SelectedItem = ""
cmbYear.SelectedItem = 0
txtAddress.Text = ""
txtOccupation.Text = ""
txtLastname.Select()

MySqlConn.close()

  1. 永远不要从依赖用户的某些字符串的字符串构建查询。这使您容易受到SQL注入攻击（尝试在其中一个名称字段中添加一个带有撇号的名称并观察一系列错误。然后，如果您不进行清理，那么实现具有恶意意图的人可能会严重损坏您的数据库您的输入）始终尽可能参数化您的查询!!

  2. 不要重复自己！（AKA DRY原则）如果你发现自己在同一个地方复制/粘贴相同的代码块，那就意味着你做错了什么。在这种情况下，你不得不坚持认为你有一个循环，并确保你的输入字段被清除，你只需复制代码将它们清除到代码路径中的3个不同的地方。如果您发现需要在整个程序代码路径中重复运行相同的代码，则将其概括并将其放入函数中。你的眼睛和下一个人的眼睛阅读/维护你的代码会很感激！

  3. 你需要更多关于SQL的知识/经验，没关系，每个人都必须从某个地方开始。在示例中，我删除了所有选择的查询，转而尝试一个插入根据该1查询的结果查询和分支逻辑。更容易阅读/维护。此外，Identity值应该由您的sql实例处理，而不是在代码中。您通常希望它们按顺序使用以避免冲突，并且您不希望它们被最终用户修改/可见。更正ID列的属性允许删除随机生成代码。请记住，当您插入带有标识列的表时，您不需要在INSERT语句中包含标识列（SQL将为您填充该列）

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