Using Transactions

Description

Many databases allow you to perform record updates within the context of a transaction. A transaction is useful when you want to make multiple updates or no updates at all. You bracket the INSERT, DELETE, or UPDATE commands with the SQL::Connection BeginTransaction(?) and CommitTransaction(?) methods. In the case when you cannot complete all the required updates, you conclude with the RollBackTransaction(?) method instead of the CommitTransaction() method. Suppose you want to copy records from the Product table to the New_Product table. Then, after you have confirmed the copy, you want delete these records from the Product table.

Before proceeding, start Access, open Alphasports.mdb, copy the Product table and its data, and name the copy ProductA. Make a second copy of the product table without its data. Name the copy ProductB.

First, create and define variables. The select_cmd will select the records to copy. The delete_cmd will select the records to delete.

dim conn as sql::connection
dim select_cmd as C
dim delete_cmd as C
select_cmd = "select * from ProductA"
delete_cmd = "delete * from ProductA"

Establish the connection. If there is an error, display a message, and end the script.

if .not. conn.open("{A5API=Access,FileName='C:\Program Files\A5V8\MDBFiles\Alphasports.mdb',UserName='Admin'}") then
    ui_msg_box("Error", "Could not establish connection" + crlf()+ conn.CallResult.text)
    end
end if

Select the data to copy. If there is an error, display a message, and end the script.

if .not. conn.execute(select_cmd) then
    ui_msg_box("Error", "Could not execute query" + crlf()+ conn.CallResult.text)
    conn.close()
    end
end if

If the records were established, it is time to begin the transaction with the BeginTransaction(?) method.

conn.BeginTransaction()

Copy records from ProductA to ProductB. If there is an error, roll back the transaction with the RollBackTransaction(?) method, display a message, and end the script.

if .not. conn.InsertData("", "ProductB", conn.ResultSet)
    ui_msg_box("Error", "Could not insert data into ProductB")
    conn.RollBackTransaction()
    conn.close()
    end
end if

Delete the records in ProductA. If there is an error, roll back the transaction, display a message, and end the script.

if .not. conn.execute(delete_cmd)
    ui_msg_box("Error", "Could not delete data from ProductA" + crlf()+ conn.CallResult.text)
    conn.RollBackTransaction()
    conn.close()
    end
end if

Finally, commit the transaction and close the connection.

conn.CommitTransaction()
conn.close()

Limitations

Desktop applications only. Not available in Community Edition.