disclaimer: I must use a microsoft access database and I cannot connect my app to a server to subscribe to any service.
I am using VB.net to create a WPF application. I am populating a listview based on records from an access database which I query one time when the application loads and I fill a dataset. I then use LINQ to dataset to display data to the user depending on filters and whatnot.
However.. the access table is modified many times throughout the day which means the user will have “old data” as the day progresses if they do not reload the application. Is there a way to connect the access database to the VB.net application such that it can raise an event when a record is added, removed, or modified in the database? I am fine with any code required IN the event handler.. I just need to figure out a way to trigger a vb.net application event from the access table.
Think of what I am trying to do as viewing real-time edits to a database table, but within the application.. any help is MUCH appreciated and let me know if you require any clarification – I just need a general direction and I am happy to research more.
My solution idea:
- Create audit table for ms access change
- Create separate worker thread within the users application to query
the audit table for changes every 60 seconds - if changes are found it will modify the affected dataset records
- Raise event on dataset record update to refresh any affected
objects/properties
Couple of ways to do what you want, but you are basically right in your process.
As far as I know, there is no direct way to get events from the database drivers to let you know that something changed, so polling is the only solution.
I the MS Access database is an Access 2010 ACCDB database, and you are using the ACE drivers for it (if Access is not installed on the machine where the app is running) you can use the new data macro triggers to record changes to the tables in the database automatically to an audit table that would record new inserts of updates, deletes, etc as needed.
This approach is the best since these happen at the ACE database driver level, so they will be as efficient as possible and transparent.
If you are using older versions of Access, then you will have to implement the auditing yourself. Allen Browne has a good article on that. A bit of search will bring other solutions as well.
You can also just run some query on the tables you need to monitor
In any case, you will need to monitor your audit or data table as you mentioned.
You can monitor for changes much frequently than 60s, depending on the load on the database, number of clients, etc, you could easily check ever few seconds.
I would recommend though that you:
Keep a permanent connection to the database while your app is running: open a dummy table for reading, and don’t close it until you shutdown your app. This has no performance cost to anyone, but it will ensure that the expensive lock file creation is done only once, and not for every query you run. This can have a huge performance import. See this article for more information on why.
Make it easy for your audit table (or for your data table) to be monitored: include a timestamp column that records when a record was created and last modified. This makes checking for changes very quick and efficient: you just need to check if the most recent record modified date matches the last one you read.
With Access 2010, it’s easy to add the trigger to do that. With older versions, you’ll need to do that at the level of the form.