Update local database all modified data to server database - mysql

Question

I'm facing a problem when I want to update data from local database to server data, replacing everything that has been modified at local database. I know it might be simple but I got no idea about this, so any help will be appreciate.
In my situation, I want to use a button to upload all modified data to
the server database. Now I'm just using 2 databases at same server to do
testing.
Private Sub btnUp_Click(sender As System.Object, e As System.EventArgs) Handles btnUp.Click
localconn.ConnectionString = lctext
serverconn.ConnectionString = sctext
Try
localconn.Open()
serverconn.Open()
Dim localcmd As New OdbcCommand("select a.acc_id as localid, a.acc_brcid, a.smartcardid, a.acc_created, a.acc_modified as localmodified, b.acd_firstname, b.acd_ic, b.acd_oldic, b.acd_race, b.acd_dob, b.acd_rescity, b.acd_resaddr1, b.acd_telmobile, b.acd_email, b.acd_telwork, b.acd_modified, b.acd_accid from nsk_account a inner join nsk_accountdetail b on a.acc_id = b.acd_accid", localconn)
Dim servercmd As New OdbcCommand("select c.acc_id, c.acc_brcid, a.smartcardid, c.acc_created, c.acc_modified, d.acd_firstname, d.acd_ic, d.acd_oldic, d.acd_race, d.acd_dob, d.acd_rescity, d.acd_resaddr1, d.acd_telmobile, d.acd_email, d.acd_telwork, d.acd_modified, d.acd_accid from nsk_account c inner join nsk_accountdetail d on c.acc_id = d.acd_accid", serverconn)
localcmd.CommandType = CommandType.Text
Dim rdr As OdbcDataReader = localcmd.ExecuteReader()
Dim thedatatable As DataTable = rdr.GetSchemaTable()
'localcmd.Parameters.Add("#localid", OdbcType.Int, "a.acc_id")
'localcmd.Parameters.Add("#localmodified", OdbcType.DateTime, "b.acd_modified")
Dim localid As String
Dim localmodi As String
localcmd.Parameters.AddWithValue("localid", localid)
localcmd.Parameters.AddWithValue("localmodified", localmodi)
For Each localid In thedatatable.Rows
Dim calldata As New OdbcCommand("SELECT acc_modified from nsk_account where acc_id ='" + localid + "'", serverconn)
Dim reader As OdbcDataReader = calldata.ExecuteReader
txtSDate.Text = reader("acc_modified").ToString
If localmodi <= txtSDate.Text Then
'do nothing, proceed to next data
Else
Dim ACCoverwrite As New OdbcCommand("Update nsk_account SET smartcardid = #mykad, acc_created = #created, acc_modified = #modify WHERE acc_id ='" + localid + "'", serverconn)
Dim DEToverwrite As New OdbcCommand("Update nsk_accountdetail SET acd_firstname = #name, acd_ic = #newic, acd_oldic = #oldic, acd_race = #race, acd_dob = #dob, acd_rescity = #city, acd_resaddr1 = #address, acd_telmobile = #phone, acd_email = #email, acd_telwork = #language, acd_modified = #detmodify WHERE acd_accid ='" + localid + "'", serverconn)
ACCoverwrite.ExecuteNonQuery()
DEToverwrite.ExecuteNonQuery()
End If
Next
MessageBox.Show("Upload success", "Error", MessageBoxButtons.OK, MessageBoxIcon.Warning)
Catch ex As Exception
MessageBox.Show(ex.Message, "Error", MessageBoxButtons.OK, MessageBoxIcon.Warning)
Finally
localconn.Close()
serverconn.Close()
End Try
End Sub
any comment or suggestion will be appreciate.

Answer 1

I hope you mean table by table. I didn't read your code much but you got the idea - you need 2 connections but here where there are 2 distinct ways of doing it.
Way #1 - you can use when amounts of data (how to say it better? - not huge). You can load a DataTable object with data from server and update changed records. You can use DataAdapter and issue CommitChanges - all changed/new rows will be written to server.
NOTE: you need a mechanism that will reliably able to tell which rows are new and modified on your local DB. Are you OK if your PK in local DB will be different than on the server? You need to answer these questions. May be you need a special mechanism for PK locally. For example, add rows using negative PK integers, which will tell you that these rows are new. And use "ModifiedDate", which together with PK will tell if the row needs updating.
Way #2 - use anytime, even with larger amount of data. Take a local row and examine it. If it is new - insert, if it is existing and "DateModified" changed - do update. There are variations of how to do it. You can use SQL MERGE statement, etc.
But these are two major ways - direct row insert/update and disconnected update/mass commit.
Also, you can do it in bulk, using a transaction - update some rows-commit, and start new transaction. This will help if the application being used as you updating it.
I hope these ideas help. If you do what you do, where you have
For Each localid In thedatatable.Rows
I am not sure what localid is. It should be
' prepare command before loop
sql = "Select * From Table where ID = #1"
' you will create parameter for #1 with value coming from
' row("ID")
Dim cmd As New .....
cmd.Parameters.Add(. . . . )
For Each row As DataRow In thedatatable.Rows
cmd.Parameters(0).Value = row("ID") ' prepare command upfront and only change the value
using reader as IDataReader = cmd.ExecuteReader(. . . . )
If Not reader.Read() Then
' This row is not found in DB - do appropriate action
Continue For
Else
' here check if the date matches and issue update
' Better yet - fill some object
End if
end using
' if you fill object with data from your row -here you can verify if
' update needed and issue it
. . . . . .
Next