I am working on migrating a MS Access Database over to a newer SQL platform.
But, with all of the users who are currently using it, we're migrating slowly/carefully.
The first step is that we are re-writing the VBA code into C#, which is then deployed in a .dll along with the database.
Now, the VBA code calls into the C# to do the business logic, then the VBA continues to do the displays/UI, while Access still hosts the database.
The problem comes in that I have a report that is being run after the business logic from the C# in one place, and apparently MS Access has a cache, which clears every 5 seconds. So, the transaction that occurs in the C# code writes to the database, but the VBA code is still using the cache. This is causing errors, as the records added to the database (which the VBA report is trying to report on) don't exist in the cache yet...
I'm guessing that the C# .dll must be getting treated as a "second connection" to the MS Access database, which is what seems to typically cause this error in my searches (thinks that one process is writing, and the other is reading).
Since the cache is cleared out every 5 seconds, we can just put the process to sleep, and wake it up after 5 seconds, and then run the report, but that's pretty terrible for an end user.
And, making things difficult, the cache seems like it only gets used in the deployed version (so, when running from source / in debug mode, the error never happens).
Doing some searches, there seems to be plenty of people who have said "just refresh the cache." But, the question is: within VBA, how do you refresh the cache?
Any advice would be welcome.
Thanks
I've been fighting the same issue for years as I write a lot of tools around an old Powerbuilder application that has an Access MDB back end.
The cache does exist and it is VERY real. When data is inserted on a different connection than it is queried on, the cache can be directly observed and measured. It was also documented by Microsoft before they blackholed a bunch of their old articles...
Microsoft Jet has a read-cache that is updated every PageTimeout milliseconds (default is 5000ms = 5 seconds). It also has a lazy-write mechanism that operates on a separate thread to main processing and thus writes changes to disk asynchronously. These two mechanisms help boost performance, but in certain situations that require high concurrency, they may create problems.
I've found a couple workarounds that are not the best, but somewhat make due until I find something better or can re-write the app with a better back end database.
The seemingly best answer I've found (that may actually work for you since you say you need VBA) is to use JRO.RefreshCache. I've been trying to figure out how to implement this using C# or VB.net without any luck. Below is a link to a code example where you execute the RefreshCache method on your 2nd connection that needs to pull the data. I have not tested this myself.
https://documentation.help/MSJRO/jrmthrefreshcachex.htm
A workaround I've found that will deliver the query results within 500ms to 1000ms of insert time (instead of anywhere between 500 and 5000 ms - or more):
Use System.Data.ODBC instead of OleDB, with connection string: Driver={Microsoft Access Driver (*.mdb, *.accdb)};Dbq=;
If someone knows how to use the JRO.RefreshCache method with OLEDB and C# or VB.net, I'd be forever grateful. I believe the issue is it's looking for an ADO connection to be passed in, not an OLEDB connection.
I not aware of ANY suggesting that some 5 second cache exits? Where did this idea come from????
Furthermore, if you have 5 users, then you not going to be able to update their cache, are you?
In other words, the issue of some cache for one user still not going to solve or work with mutli-users anyway, is it?
The simple matter is if you load up a form with 100 reocrds, and then other users are ALSO working on that 100 rows, then all users will not see other changes until such time you tell access to re-load the form.
You can do this with a me.Refresh in the form, and then it will show changes made by other users (or even your c# code!!!).
However, that not really the soluion here.
How does near EVERY system deal with this issue?
Answer:
You don't, you "design" the software to take the user work flow into account.
So, in place of loading up a form with 100 rows of data? (which you should not, unless SUPER DUPER reason exists for doing that).
The you provide a UI in which the user FIRST searches for whatever it is they want to work on.
In other words, say you just booked a user on a tour. Now, they call the office back, and want to change some details of that tour. But, a different tour staff might pick up the phone. So, now a 2nd user opens the tour?
So, you solve that issue by NOT loading all the tours into that form in the first place.
you provide a search screen, so they can search for the user, find the user, maybe type in a invoice number or whatever.
You display the results in a pick list, and then launch the form to the ONE record (and perhaps detail records from child tables).
So there no concpet of a cache in Access anymore then there is in c#.
However, if you load up a datatable in c#, and then display that data?
Well, what about the other users on that system. They will not see changes to that data ANY MORE then the current access form.
So, if you want to update some data in c#? Then fine, but you need/want to do two things:
First, before you call any c# code that may update the current form reocrd? You need to FORCE a data save of that current record BEFORE you call any code, be it VBA code, or c# code that going to update that current reocrd the user is working on.
You can in Access save the current reocrd in MANY different ways, but the typical approach is:
' single record save - current record
if me.dirty then me.dirty = false
' VBA or c# code goes here.
' optional refresh the current form to reflect changes
me.Refresh
So, in most cases, it is the "design" of your software that will solve this issue.
For example, in the tour example, or in fact ANY system, the user can't work, can't update, and can't do their job UNLESS they first find/search and have a means to bring up that form + record data in the first place.
So, ANY typical good design will:
Ask the user for that name, invoce number or whatever.
Display the results of the search, and THEN allow the user to pick the record/data to work on. When they are done, they close that form and are RIGHT BACK to the search form to do battle with the next customer or task or phone call or whatever.
So, a search form might look like this:
In above, I typed in smi, and then displayed a pick list.
The user can further type in say part of the first name, and thus now get this:
So, maybe they type in a invoice number, customer number, booking number or whatever.
So, you display the results, and then they can select the row or "thing" to work on.
thus, we click on the row (or above glasses button), and then jump to the ONE record.
so, the user does whatever they have to do with the customer. Now, when done, they close the ONE thing, the ONE main reocrd.
This not only saves the data (so others in the office can now use that booking data), but it also means the data is saved. and they are NOW right back at the search screen, ready to do battle with the next customer.
So, not only does this mean we have a VERY bandwith friednly design (we only pull the one main reocrd into that form), but it also is better for work flow.
The Access form's cache thus becomes a non issue, since we only dealing with the one record.
And as I pointed out, if the system is multi-user, then you NOT going to be able to udpate and deal with multiple users cached data anyway, are you?
Think of ANY system you EVER used from a software point of view.
When you use google, does it download the WHOLE internet, and then you use ctrl-f to search megs and megs of data in the browser?
Nope!
you search first, get a list of that search, and THEN pick one!!
And when that list is display, maybe others on the internet are udpateing, and add new data - but if that was cached in your browser, then it would not work!!!
And same goes for a desktop accounting system. You don't load up all accounts, and THEN have the user go ctrl-f to search all the data. You search for the customer, invoice number and PICK ONE to work on.
And it does not make sense to load up a form with 1000 customers, and then go ctrl-f to find that customer. Same goes for a instant banking machine. It does not download ALL customers and THEN let you search. It asks you FIRST to get what you need. So, be it browser based, desktop based, or JUST ABOUT ANY software you use?
You quite much elminate the cache issue, since not pre-loading boatloads of data, but asking and letting the user search for the data they need.
So, in regards to the Access form data and cache?
If you are on a form, and call VBA code, or c# code or whatever?
If that code update the current form, you have NO MORE OR LESS of a issue when calling VBA code, or c# code!!!! If that code updates the current form, and the reocrd is dirty (has pending edits), then you get that message about the current form's reocrd having been udpated by another user!!!
So, your cache issue does NOT IN ANY WAY exist MORE or LESS as a issue in typical Access software.
As a genreal rule, if you are on a form with pending edits, and say want to pop up some form to edit releated data?
You have to ensure that pending edits are SAVED before you launch an form that can edit the same data, or run code that can/may edit that data.
As a result, ZERO cache issues should exist, and they no more or no less exist when calling sql or VBA update code in a form then calling some c# code from that form.
So, write the pending update for that form.
Then run your VBA, SQL, or c# code.
And then do a me.Refresh to display any changes made by those external routines.
there is no documetjion, or ANY article I can find that suggests some kind of 5 seocnd cache or update - it is a urban myth, and your software challenge here in regards to use c# or VBA, or even SQL server stored procedures?
They are all the same issue, and I dare say that often access is used as a front end to SQL server, and ALL OF the SAME issues exist when using SQL server with ms-access.
Currently I am trying to run a SAS program using VBA. Using the SAS Add-In For Microsoft Office, I created a stored process that contains a generic code that creates a dummy table. Inside SAS EG, I am able to run the Stored Process normally, and also inside the Excel environment, using the InsertStoredProcess function of the SASExcelAddIn object. Regardless of the environment used to run my Stored Process, the behavior of the SAS Sessions are the same: one session is created when I start to run and another one is created during the process. However, that is where my problem comes. When the process finishes, I continue with the two sessions as active, and every time I try to run again my Stored Process, one new session is created over the ones that already existed. The sessions close only when I manually disconnect from the SAS Server I'm connected or when I close the Excel. Since my organization allows only three concurrent sessions, this is becoming a big problem for me.
I already tried to use the ABORT macro function inside my code, the rc=stpsrv_session('delete') command and delete the Stored Process from the Excel worksheet, and none of them solved my problem.
Any ideas of what I'm missing here? Is there a way to end the SAS Session after the Stored Process ends?
First of all, you shouldn't use VBA to do any of this. If in Office products, use VSTO and C#. I am in the throes of converting thousands of lines of VBA to C#/VSTO. VBA is very obsolete which is why the code is being converted.
Second, EG is built using C# so it is more natural to use. You can even create custom tasks using C# in EG.
You need to close out your sessions after they are started. See this post at SAS for how to close out your sessions in VBA: https://communities.sas.com/t5/SAS-Enterprise-Guide/Calling-SAS-through-VBA/td-p/79673
Again, you should stop using VBA and switch over. It will be much easier. VSTO is free and is made to interact with Office. Use Visual Studio to create your project. The C# code for working with SAS can be found using any of Chris Hemendinger's post (SAS community manager) or you can refer to links on my github repos here: https://github.com/savian-net
Currently I am in the process of building an updated Microsoft Access database for our affiliated hospital to keep a timeline of documentation for potential medical studies. The database itself is standalone, so there is no real back end to speak of (which hurts me, but I have no control over how they handle their data). It currently holds only one table with all the necessary fields needed. I'm looking to have reports generate automatically every week, month, quarter, and year. However, I must admit my vba coding abilities are spotty at best. My questions are this:
What code would I need to use to generate said reports?
Would I need to create separate queries just for each type of report based on when it needs to be generated, or can I code it all in one query without the different codes interfering with each other?
If any other information or clarification is needed, I'd be happy to give you what I can.
When calling a Report from VBA or from a macro, two things could be usefull to you:
providing a condition, like
docmd.OpenReport "someReport",acViewPreview,,"[examDate] > Date() - 30"
providing an OpenArg, which can be used by vba in your report to change the periodicity for example ("M" for Monthly and "w" for Weekly"), like
docmd.OpenReport "someReport",acViewPreview,,"[examDate] > Date() - 30",,"W"
Those tricks should allow you to design a report ONCE, then use it with dynamic time range and grouping.
If you don't want to use VBA, for creating automatic reports printing/export you'll need:
Create reports which don't require user entry, use date functions for querying required date intervals.
Create macroses for starting reports and closing the database, no VBA knowledge required
Create tasks in Windows Task Scheduler for starting MS Access at requred days/time. Command line should contain parameters for opening specified database and starting specified macro (/x macro_name). Parameters description you can find, for instance, here
.
The comments say it all.
Access is designed to make report writing of the nature you describe very easy, and a lot can be achieved without using VBA at all or macros for that matter.
If you want to use the same report to display the same sets of data for different date ranges (or perhaps with other changes in criteria), you should prompt the user to enter a date range or the other criteria that will cause the data displayed to be changed. (ie the parameters they entered are used in the query to change the data returned).
This is infinitely preferable to having many many reports and queries that are all the same except they get data for a different set of criteria.
There are many Access Programming books that will help you re-learn these skills. I have found this channel useful https://www.youtube.com/user/ProgrammingMadeEZ/search?query=reports for other Access videos, but it's not as useful for reports.
Harvey
how to do live updates to one cell to another cell?? I don't know, is it call synchronized or live updates, what im trying to do, i want my cell to update to another sheet, if i change something or values in sheet1 cell 1 then sheet2 cell 1 should change it automatically.. any1 have any ideas ????do i have to do live change or live updates or its a synchronizing or how do i code it, i never did anything like that before.....
sub worksheet_change()
if sheets("sheet1") = sheets("sheet2") then
do liveupdate
end if
end sub
DDE
If it's on the same computer, you can do something called DDE and make DDE based functions.
DDE is an old but still very well used technology (especially in the financial industry) which stands for Dynamic Data Exchange. That will enable you to control values in the cells of one worksheet from code driven through another.
Search for DDE examples, DDE MSDN, etc. and you'll find tonnes of simple examples out there.
DCOM ??
For a while, MSFT wanted to extend DDE and similar technologies across networks, like Distributed COM but security issues got in the way and common sense prevailed.
RTD:
A bit more involved and better (IMHO) method is creating a simple RTD server (Real Time Data Server) that reads data from your sheet, and pumps it across a network or simply to another instance of Excel on your computer.
Either of these methods can be used to distribute live stock feeds, etc. coming onto expensive subscription terminals across a network (be aware of the licensing issues though for spreading any data around using these techniques).
RTD information can also be found with simple examples to set up an RTD server scattered across google search results.
Hope it was helpful.
I am currently writing an utility that takes two different sets of data from an excel document and sends it to two different web services. Each set of data has it's own button that sends the data to the web service. When the a button is clicked, the corresponding web service then returns data depending on the input values.
What I am trying to do is so that this utility can be distrobuted and used by a wide variety of people. What they are going to do is they are going to be synchronizing there particular cells of their own excel document to the corresponding cell in my utility. Using simple excel formulas. For example:
c:\temp\[book1.xls]sheet1'!a1
Now what I am trying to do is automatically "click" the button, or update, on my utility when the user links their cell to its corresponding cell on my utility.
I have tried the selection change event on my page. But it doesn't actually process until my utility is active, or clicked on.
Is there a way to make my utility automatically update? It would be especially awesome if somehow it did this while my utility was closed. So when the user opens it it is already filled with their information, and the outputs are correct.
The requirements:
you need to guarantee that when a user is using excel your app can collect the data. Your app may not be running at the time. You need the Worksheet_SelectionChange() event to fire automatically not just when your app is active.
Solution:
Basically in order to guarantee that the Worksheet_SelectionChange() is running all the time, and in order to guarantee that whenever the user opens an instance of excel you are able to collect and process the data/formulas entered into the particular target range address you need to wire up the selectionchange event inside of a VB.NET Excel COM Addin. There are several ways to do this, but since your using VB.NET your best off using the newest approach which is building a VSTO COM Addin.
There are numerous other questons available on how to best build a VSTO addin (some in C# some in VB.NET but all this information is exactly the same for both, just different syntax).
So you will need two projects. Your existing one, plus a Excel VSTO addin (which you can also do in VB.NET).
Now inside the selectionchange event you should make sure that your code handles the target range correctly; ie. make sure you check for non-contigious groups of ranges with a selection... A1:B1;D2:E2 and copy the data to your app. You may consider using a format such as xml to serialise the latest data from excel so that if your app is not open at the time, it can deserialise and read back the data stored for it the next time it is opened. I guess it really depends how your handling the data (i.e. is it for loading into a datagrid?) and whether you are going to do further processing and store it somewhere else later (in which case maybe you can put it straight into a database from the addin in excel).