VB网络&x2B;子串+;Mysql+;检查行
我有一个简单的表单,有一个按钮和两个文本框VB网络&x2B;子串+;Mysql+;检查行,mysql,vb.net,substring,Mysql,Vb.net,Substring,我有一个简单的表单,有一个按钮和两个文本框 Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click MysqlConn = New MySqlConnection(ConfigurationManager.ConnectionStrings("db.My.MySettings.dbConnectionString").ToString) Try '
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
MysqlConn = New MySqlConnection(ConfigurationManager.ConnectionStrings("db.My.MySettings.dbConnectionString").ToString)
Try
'MysqlConn.Dispose()
'MysqlConn.Close()
MysqlConn.Open()
Dim str As String
str = "SELECT substring_index(substring(path,1,locate(substring_index(path,'\\',-1),path)-2),'\\',-1)as PATH FROM foto where id_product = '" & TextBox2.Text & "'"
Dim dbCommand As New MySqlCommand(str, MysqlConn)
Dim dbReader = dbCommand.ExecuteReader
While dbReader.Read()
If IsDBNull(dbReader(0)) OrElse String.IsNullOrEmpty(dbReader.GetString(0)) Then
TextBox1.Text = "0"
Else
TextBox1.Text = dbReader.Item("PATH")
End If
End While
Catch ex As Exception
MessageBox.Show(ex.Message)
Finally
MysqlConn.Dispose()
End Try
End Sub
当我输入textbox2“1”时,我得到了所需的值。
但是当我输入“2”时,这个id\u产品不存在,我没有“0”。
它是空白的,Textbox1有我以前的值
我做错了什么???如果查询没有返回任何记录,那么代码不会进入while循环(dbReader.Read return false),因此您不会将文本框设置为“0”,但也应该开始使用参数化查询。避免可能的解析错误非常重要,主要是避免 因此,您可以测试您的查询是否生成了任何验证DataReader属性HasRows的记录
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Using MysqlConn = New MySqlConnection(ConfigurationManager.ConnectionStrings("db.My.MySettings.dbConnectionString").ToString)
Try
MysqlConn.Open()
Dim str As String
str = "SELECT substring_index
(substring(path,1,
locate(substring_index(path,'\\',-1),path)-2),
'\\',-1) as PATH
FROM foto where id_product = @pid"
Dim dbCommand As New MySqlCommand(str, MysqlConn)
dbCommand.Parameters.Add("@pid", MySqlDbType.VarChar).Value = textBox2.Text
Using dbReader = dbCommand.ExecuteReader
if dbReader.HasRows Then
While dbReader.Read()
If IsDBNull(dbReader(0)) OrElse String.IsNullOrEmpty(dbReader.GetString(0)) Then
TextBox1.Text = "0"
Else
TextBox1.Text = dbReader.Item("PATH")
End If
End While
else
TextBox1.Text = "0"
End If
End Using
Catch ex As Exception
MessageBox.Show(ex.Message)
End Try
End Using
End Sub
如果查询未返回任何记录,则代码不会进入while循环(dbReader.Read return false),因此不会将文本框设置为“0”,但应该开始使用参数化查询。非常重要的是,如果它不存在,代码甚至不会进入While循环。您应该设置一个断点并逐步执行。另外,不要连接查询,请使用参数!