问题
I hope the title is enough to understand my problem, I already installed whats need to run the ADO.NET, I already have a connection string in my module and data query in my class,
Imports System.Data
Imports System.Data.OleDb
Module GlobalVariables
Public sGlobalConnectionString As String
Friend conString As String
Public dr As OleDbDataReader
Sub Main()
Dim sGlobalConnectionString As New OleDb.OleDbConnection
Dim sDataserver As String
Dim sDatabaseName As String
Dim sDatabaseConnection As String
sDataserver = "localhost"
sDatabaseName = "employee"
sDatabaseConnection = "Driver={MariaDB ODBC 3.1 Driver}; SERVER=" & sDataserver & "; UID=root;PWD=******; Database=" & sDatabaseName & "; PORT=3307; OPTION=3"
sGlobalConnectionString = New OleDb.OleDbConnection(conString)
End Sub
End Module
this is my class
Imports System.Data.OleDb
Public Class clsDataQuery
Public Shared Sub Class_initialize()
Dim con = New OleDb.OleDbConnection
con.ConnectionString = sGlobalConnectionString
con.Open()
End Sub
Public Shared Sub Class_Terminate()
Dim con = New OleDb.OleDbConnection
If Not con Is Nothing Then
con.Close()
con = Nothing
End If
End Sub
Public Function GetRecordDataSet(ByVal sStoreProcName As String, ByVal sParameterList As String)
Dim cmd As New OleDbCommand()
Dim arrParameter, arrParamName
Dim sParamName As String
Dim sDataValue
Dim lCtr As Long
On Error GoTo errhandler
cmd.Connection = New OleDb.OleDbConnection
cmd.CommandTimeout = 1800
cmd.CommandText = CommandType.Text
If Not Trim(sParameterList) = "" Then
arrParameter = Split(sParameterList, "|", , vbTextCompare)
If UBound(arrParameter) >= 0 And IsArray(arrParameter) Then
For lCtr = 0 To UBound(arrParameter)
arrParamName = Split(arrParameter(lCtr), "$", , vbTextCompare)
sParamName = arrParamName(0)
sDataValue = arrParamName(1)
cmd.Parameters.Item(sParamName) = sDataValue
Next lCtr
End If
End If
GetRecordDataSet = cmd.ExecuteReader
cmd = Nothing
Exit Function
errhandler:
MessageBox.Show("Records Not Found!!!")
End Function
End Class
if this button is click, the value of Textbox1.text will search in the database if it is exist, if exist it will continue into another form if not error message will appear, how do i do that?
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim username = txtbox_lastname.Text
If username <> "" Then
Try
clsDataQuery.Class_initialize()
Catch ex As Exception
MessageBox.Show("No Record Found")
End Try
Else
MessageBox.Show("No Record Found!!!")
End If
End Sub
回答1:
If this is MariaDb then you want to use the provider for MySql. Not ODBC and not OleDb. No wonder you are having problems. There is not much information available for this database compared to the usual Access database used for beginners.
Do not declare database objects anywhere but the method they are used in. You can declare a Private variable for the connection string at the class level.
Although one of these is a Module level variable and one is a local variable, it is very confusing and bad practice. Why would you call a connection object a String?
Public sGlobalConnectionString As String
Dim sGlobalConnectionString As New OleDb.OleDbConnection
BTW, it is fine to declare and initialize your variables in a single line.
Dim sDataserver = "localhost"
You create a new connection on the first line of Sub Main, then you throw it away and create another new connection on the last line. Since sDataServer and sDatabaseName are hard coded why not just put the literal values directly into the connection string.
After all that you pass conStr to the constructor of the connection instead of sDatabaseConnection. Why were you building sDatabaseConnection (another misnomer, it is not a connection, its a string) and then never use it. Has conStr been set elsewhere?
At any rate, throw out the whole module.
Moving on to your DataQuery class. First, the name should begin with an upper case letter.
Get rid of Class_initialize. We don't want to create or open any connection except in the method where it is used. You never call Class_Terminate so dump that too.
The GetRecordDataSet method...
Functions in vb.net require a datatype. The old VB6 syntax of assigning the return value to the name of the function will work but it is not the .net way. In vb.net we use the Return keyword.
You have not initialized or given a datatype to arrParameter, arrParamName or sDataValue which violates Option Strict. (You do have Option Strict On, don't you?)
On Error GoTo errhandler is a sad leftover from VB6. .net languages have structured error handling with Try...Catch...Finally...End Try.
cmd.Connection = New OleDb.OleDbConnection sets the connection property however this new connection has no connection string.
cmd.CommandText = CommandType.Text Now this is just silly. What I think you want is cmd.CommandType =CommandType.StoredProcedure
Using...End Using blocks take care of declaring, closing and disposing database objects even if there is an error. You don't want to return a DataReader because a reader requires an open connection. cmd.ExecuteReader returns a DataReader. I used the reader to load a DataTable and returned the DataTable.
It seems you are trying to develop a factory pattern but it is way too advanced for your. Just pass value and call a method specific to what your are searching for. You want your DataQuery code to be independent from your user interface. The Button code doesn't care where the data is coming from. It could be a database, a text file, or a web service. Likewise the DataQuery code doesn't know where the values are coming from. It could be a WinForms app, a web application or a phone app.
Public Class DataQuery
Private Shared ConStr As String = "server=localhost;userid=root;database=employee"
Public Shared Function SearchByLastName(ByVal LName As String) As DataTable
Dim dt As New DataTable
Using cn As New MySqlConnection(ConStr),
cmd As New MySqlCommand("Select * From PutTableNameHere Where LastName = @LName", cn)
cmd.Parameters.Add("@LName", MySqlDbType.VarChar).Value = LName
cn.Open()
Using reader = cmd.ExecuteReader
dt.Load(reader)
End Using
End Using
Return dt
End Function
End Class
Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
Dim dt As DataTable = Nothing
If txtbox_lastname.Text <> "" Then
Try
dt = DataQuery.SearchByLastName(txtbox_lastname.Text)
Catch ex As Exception
MessageBox.Show(ex.Message)
End Try
End If
DataGridView1.DataSource = dt
End Sub
回答2:
Before answering, I really think that the GetRecordDataSet() at the very least a darn good tidy up, better yet removed from history
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim username = txtbox_lastname.Text
If username <> "" Then
Try
clsDataQuery.Class_initialize()
Dim reader = GetRecordDataSet("storedProcName", txtbox_lastName.Text)
Do While reader.Read()
'Process record etc
Loop
Catch ex As Exception
MessageBox.Show("No Record Found")
End Try
Else
MessageBox.Show("No Record Found!!!")
End If
End Sub
Might be a bit rough, but should get you heading in the right direction
来源：https://stackoverflow.com/questions/66043400/how-do-i-get-the-data-to-my-database-using-vb-net-class-module-and-form