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Use global ADODB.Connection object

Created by: trini at: 9/20/2006 10:58 AM (4 Replies)

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9/20/2006 10:58 AM	Rate (0)
trini Posts: 19 Rating: (8)	Hi, I am accessign an external database using an ADODB connection object. To save time -everytime I create a ADODB connection an open it it takes some seconds- I create only one ADODB connection object and store it in DataSet object. So, everytime I need some data from the database, I use the object in DataSet to access it. This works ok, but I was told that ADODB connection object does not support multithreading, so I think I need to assure that one ADODB connection object will not be accessed from different threads to avoid problems. To start, as it seems that the code in actions and the code associated to objects in pictures are executed in different threads, I use two ADODB connection objects, onefor the code in actions and one for the code in pictures. Do you think this is enough? or perhaps different actions are executed in different threadsor code of different pictures is executed as well in different threads? Thanksfor yourhelp, Trini. -WinCC v6 SP4-
trini Posts: 19 Rating: (8)
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9/20/2006 8:36 PM	Rate (0)
Salma Gold Member Joined: 9/27/2005 Last visit: 11/27/2007 Posts: 1398 Rating: (151)	My knowledge of this area is limited because of the limitations of VBS [:P] I know that VBS picture scripts run on two separate threads - one for property scripts and one for event scripts. You can see this clearly if you run a VB debugger such as the MS Script Debugger. So an object created in a property script can't be used in an event script. And then the Global Actions are a whole other headache! It's a messy problem and I too would like to hear other peoples recommendations. Maybe the best way is to create some external DLL that does the ADO handling?

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9/27/2006 9:11 AM	Rate (1)
CKa Regular Member Joined: 10/13/2005 Last visit: 9/3/2024 Posts: 33 Rating: (3)	Hi. I often use ADO and ADO.NET in order to connect to databases (almost always Ms SQL server). I believe that the recommended way is to keep a connection open only for as long as it is needed. Opening connections for me takes milliseconds and the sql statement or query is usually what takes most time, so I'm unsure why only opening the connection takes seconds for you. I also recommend to read about connection pooling which at least SQL server uses (identical connectionstrings share the same connection). Here's a link to that: http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpguide/html/cpconconnectionpoolingforsqlservernetdataprovider.asp

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9/27/2006 12:42 PM	Rate (0)
Reuben Posts: 70 Rating: (13)	Hi I also use ADO Connections quite a lot, in C-Script and in VB script. I tried using global objects for a while, but for the reasons mentioned this can be problematic. Also, if you use a global connection and connect once, you probably have to implementcode to handle connectivity problems, ie: database server is rebooted so your connection becomes invalid. Usually I am using the ADO database connection to log values obtained via GetTagWait functions (see other thread for that saga), and so the database connection is the least of the delays. With MS SQL Server, creating and freeing the ADO objects every time I perform a database operation has no noticableimpact. I assume the MS SQL Server is optimizing itself for this. If you are using some other database, then maybe it's ADO interface behaves differently. As for DLLs - I once used a DLL to perform SQL operations, and found that the behavior was different depending on whether the DLL functions were called from Global Actions or from Graphics events - in that particular case the DLL interfaced to an Oracle database and the SQL insert operations failed in a global action, but worked if executed from, say a button on a picture (this was WinCC version 5, so maybe no longer a problem).
Reuben Posts: 70 Rating: (13)
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11/19/2009 9:43 AM	Rate (0)
Icebear17 Experienced Member Joined: 2/22/2006 Last visit: 10/26/2024 Posts: 74 Rating: (3)	Unfortunatly, it is still a problem. We are using C-Scripts for database-operations and if they are called from GlobalActions, the Script.exe crashes. Not on every call, but over a period of app. one week. We are using WinCC 6.0+SP4+HF13. In WinCC 7 it is different, it seems that Script.exe doesn't crash but something is happening in the background, because when we close the project, there is an error "no database table". There is also a strange behavior of Fields->Value: it should return a VARIANT, but it seems to be an BSTR. The following line is working, but in my opinion it should not work: strcpy(NfName, grs->Fields("Bezeichnung")->Value); It should be necessary to use a conversation WideCharToMultiByte(...) but I found no working solution for this yet. If I set a 1-byte-char-pointer to grs->Fields("Bezeichnung")->Value to look what is standing there, the first 4 bytes are mysterious. for (p=grs->Fields("Bezeichnung")->Value,i=0;i<20;i++,p++) printf("%c ", *p); Does anybody has the same problems or an idea for this?

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