I am building an application that connects to a mysql database. I set up the data connections and data source (data set) and have begun working on development, going back and forth between adding tables and views to the database and adding forms and components to the application.
I have up to now used the "Configure Data Source with Wizard" wizard to refresh the dataset in the application. Sometimes it takes a couple click throughs to get it to fully load the changes, but that's not the end of the world.
Today, without me knowingly changing anything, when I click on the wizard button, the frame of the wizard opens and closes instantly.
My data is accessible, and the parts of the application already developed work just fine, but I don't know how to add new tables and views to my project. My worry is that something went screwy in one of the auto generated dbDataSet.* files.
I'm happy to provide more information if that will help.
To answer my own question for whomever comes here next:
I came across this solution:
https://stackoverflow.com/a/4749044/7640114
It links to a microsoft.com page that is no longer available, but copies the relevant information. Finding the corresponding files is not hard, but knowing what the wrong Provider is may not be so simple.
Mostly because of a lack of patience, I just went with the second option and deleted the entire folder, which may have been overkill. It worked, and I have access to the wizard again and can continue development, but it also wiped out my workspace layout which I now have to rebuild from my memory.
Win some/loose some. In the end, I suggest being more delicate and removing lines of code from DefaultView.SEView first, and then moving on to trying to delete the file and the folder if nessasary.
I'm developing a web application that also use Wordpress as part of it. I want to use Liquibase to track my database changes.
How to handle database changes made by automatic update script of Wordpress?
Can I just ignore them? and put only my own changes in Liquibase changelog file?
You could do a diffChangelog of the schemas after each WordPress upgrade so that Liquibase could keep track of the changes. You can just ignore them though - Liquibase doesn't really care about unknown schema objects. The only issue would be if your changes and the WordPress changes conflicted.
You can and should just ignore them.
Liquibase just does one thing. It keeps track of the fact that:
a certain command (say, createTable)...
...that looked a certain way at time 0 (the name of the table, its columns, etc.)...
...was definitively executed at time 0 (it stores this record in DATABASECHANGELOG).
That's it. It is not a structure enforcer or a database state reconstitution engine. It is quite possible—and permitted, and often expected—that the database will be changed by other tools and Liquibase will have no idea what went on.
So just keep your commands in your changelogs, don't worry about preexisting database structure, use preconditions to control whether or not your changesets run, and ignore everything else that might be going on in the database that happened due to other tools.
We have an issue we are seeing where a table seems to be getting reset, the records are deleted and the primary key is reset. This then causes issues with another table that joins to it. I have a theory it might be to do with the connection dropping out when trying to retrieve info from the data context and then submitting a blank/default table. It looks like the data context is being reused rather than creating a new one for each unit of work which I think is the wrong thing to do but i was wondering if this would be the cause of the issue?
when i used local database, i faced same problem. in every run,
visual studio adds main database files into the debug folder and overwrites.
so i see blank database after run. but there is no problem,
because after releasing the solution it happenings not same, and problem disappears.
I have an Access 2003 database using MS-JET linked tables (that is, there are two *.mdb files). The overall task is to move to SQL server. However the existing databases have multiple fields with spaces and other characters that upset both of the Access migration wizards. So the intermediate task is to make a version of the existing mdb's with updated field names.
"Simply" changing field names in the UI mdb file doesn't work, because of the linked tables being read-only in that mdb. Updating the Data mdb file field names first doesn't work because the UI mdb then throws a wobbly on startup and Access gives up.
I'm looking for suggestions, but options I can see are:
re-integrate the Data mdb back into the UI one, do the updates, then re-export the data. Seems very risky to me (system is live, don't want to play with data any more than strictly necessary).
I've looked at several answers here relating to changing ODBC details with VBA code, which is interesting, and I can see how I might be able to programmatically edit the linked tables' names. Is this going to work? Is there a better way?
Unlink all linked tables, then edit in UI mdb the remaining forms, reports, queries (but would that work??) and edit the Data mdb fields, and finally relink everything. Will it fall apart?? ... seems likely.
Any suggestions?
Ruth
I go through this process every time I take over an existing Access application -- I have to bring it up to my own standards for naming conventions before I do anything significant with it. Recently I built a quick-and-dirty utility to rename fields. It was made for me and has very little error recovery, and a UI that is ugly, but it might be faster than doing it yourself.
See what track name autocorrect offers. How Name AutoCorrect Works in Microsoft Access
Make a copy of your UI MDB, delete the linked tables, then import them (as tables rather than links) from the Data MDB. Once you enable autocorrect, Access will attempt to propagate your field name changes wherever they are used (in forms for example). Unlikely it will catch 100% of the necessary changes, but it should resolve a big chunk of them. You would then need to manually track down and fix the rest.
Once you have everything fixed, you could use that MDB version to "upsize" your tables to SQL Server. However, one huge complication is if the original database is "live" while you're making changes to the new version. If you absolutely can't take the database out of service in the interim, you could discard the data from the new tables, then use "append" queries which alias the old to new field names to pull in the latest data.
INSERT INTO NewTable (emp_id, another_field)
SELECT
[emp ID],
[another field]
FROM OldTable IN 'C:\somefolder\Data.mdb';
Finally, a warning about autocorrect: do not leave it enabled in the production version of your database because strange things can happen. The safest approach IMO is to turn it on, complete your object name changes, then turn it back off again.
You might find Rick Fisher's Find and Replace tool helpful if you need to propagate name changes through the project. I've relied on it for years (though I don't do much Access development lately): http://www.rickworld.com/products.html
I think this tool will change the names of tables and fields for you but I am not sure. I mostly used it for finding references to tables and queries in other queries, form and report properties, and VBA code.
I have created an MS Access 2003 application, set up as a split front-end/back-end configuration, with a user group of about five people. The front end .mdb sits on a network file server, and it contains all the queries, forms, reports, and VBA code, plus links to all the tables in the back end .mdb and some links to ODBC data sources like an AS/400. The back end sits on the same network file server, and it just has the table data in it.
This was working well until I "went live" and my handful of users started coming up with enhancement requests, bug reports, etc. I have been rolling out new code by developing/testing in my own copy of the front-end .mdb in another network folder (which is linked to the same back-end .mdb), then posting my completed file in a "come-and-get-it" folder, alerting the users, and they go copy/paste the new front-end file to their own folders on the network. This way, each user can update their front end when they're at a 'stopping point' without having to boot everyone out at once.
I've found that when I'm developing now, sometimes Access becomes extremely slow. Like, when I am developing a form and attempt to click a drop-down on the properties box, the drop-down arrow will push in, but it will take a few seconds before the list of options appears. Or there's tons of lag in selecting & moving controls on a form. Or lots of keyboard lag.
Then, at other times, there's no lag at all.
I'm wondering if it's because I'm linked to the same back end as the other users. I did make a reasonable effort to set up the queries, forms, reports etc. with minimal record locking, if any at all, depending on the need. But I may have missed something, or perhaps there is some other performance issue I need to address.
But I'm wondering if there is an even better way for me to set up my own development back-end .mdb, so I can be testing my code on "safe" data instead of the same live data as the rest of the users. I'm afraid that it's only a matter of time before I corrupt some data, probably at the worst possible moment.
Obviously, I could just set up a separate back-end .mdb and manually reconfigure the table links in the front end every time, using the Linked Table Manager. But I'm hoping there is a more elegant solution than that.
And I'm wondering if there are any other performance issues I should be considering in this multi-user, split database configuration.
EDIT: I should have added that I'm stuck with MS Access (not MS-SQL or any other "real" back end); for more details see my comment to this post.
If all your users are sharing the front end, that's THE WRONG CONFIGURATION.
Each user should have an individual copy of the front end. Sharing a front end is guaranteed to lead to frequent corruption of the shared front end, as well as odd corruptions of forms and modules in the front end.
It's not clear to me how you could be developing in the same copy of the front end that the end users are using, since starting with A2000, that is prohibited (because of the "monolithic save model," where the entire VBA project is stored in a single BLOB field in a single record in one of the system tables).
I really don't think the problems are caused by using the production data (though it's likely not a good idea to develop against production data, as others have said). I think they are caused by poor coding practices and lack of maintainance of your front end code.
turn off COMPILE ON DEMAND in the VBE options.
make sure you require OPTION EXPLICIT.
compile your code frequently, after every few lines of code -- to make this easy, add the COMPILE button to your VBE toolbar (while I'm at it, I also add the CALL STACK button).
periodically make a backup of your front end and decompile and recompile the code. This is accomplished by launching Access with the /decompile switch, opening your front end, closing Access, opening your front end with Access (with the SHIFT key held down to bypass the startup code), then compacting the decompiled front end (with the SHIFT key held down), then compiling the whole project and compacting one last time. You should do this before any major code release.
A few other thoughts:
you don't say if it's a Windows server. Linux servers accessed over SAMBA have exhibited problems in the past (though some people swear by them and say they're vastly faster than Windows servers), and historically Novell servers have needed to have settings tweaked to enable Jet files to be reliably edited. There are also some settings (like OPLOCKS) that can be adjusted on a Windows server to make things work better.
store your Jet MDBs in shares with short paths. \Server\Data\MyProject\MyReallyLongFolderName\Access\Databases\ is going to be much slower reading data than \Server\Databases. This really makes a huge difference.
linked tables store metadata that can become outdated. There are two easy steps and one drastic one to be taken to fix it. First, compact the back end, and then compact the front end. That's the easy one. If that doesn't help, completely delete the links and recreate them from scratch.
you might also consider distributing an MDE to your end users instead of an MDB, as it cannot uncompile (which an MDB can).
see Tony Toews's Performance FAQ for other generalized performance information.
1) Relink Access tables from code
http://www.mvps.org/access/tables/tbl0009.htm
Once I'm ready to publish a new MDE to the users I relink the tables, make the MDE and copy the MDE to the server.
2) I specifically created the free Auto FE Updater utility so that I could make changes to the FE MDE as often as I wanted and be quite confident that the next time someone went to run the app that it would pull in the latest version. For more info on the errors or the Auto FE Updater utility see the free Auto FE Updater utility at http://www.granite.ab.ca/access/autofe.htm at my website to keep the FE on each PC up to date.
3) Now when working on site at a clients I make the updates to the table structure after hours when everyone is out of the system. See HOW TO: Detect User Idle Time or Inactivity in Access 2000 (Q210297) http://support.microsoft.com/?kbid=210297 ACC: How to Detect User Idle Time or Inactivity (Q128814) http://support.microsoft.com/?kbid=128814
However we found that the code which runs on the timer event must be disabled for the programmers. Otherwise weird things start happening when you're editing code.
Also print preview would sometimes not allow the users to run a menu item to export the report to Excel or others. So you had to right click on the Previewed report to get some type of internal focus back on the report so they could then export it. This was also helped by extending the timer to five minutes.
The downside to extending the timer to five minutes was if a person stays in the same form and at the same control for considerable parts of the day, ie someone doing the same inquiries, the routine didn't realize that they had actually done something. I'll be putting in some logic sometime to reset this timer whenever they do something in the program.
4) In reference to another person commenting about scripts and such to update the schema see Compare'Em http://home.gci.net/~mike-noel/CompareEM-LITE/CompareEM.htm. While it has its quirks it does create the VBA code to update tables, fields, indexes and relationships.
Use VBA to unlink and re-link your tables to the new target when switching from dev to prod. It's been to many years for me to remember the syntax--I just know the function was simple to write.
Or use MS-Access to talk to MS-Access through ODBC, or some other data connection that lives outside of the client mdb.
As with all file base databases, you will eventually run into problems with peak usage or when you go over a small magical number somewhere between 2 and 30.
Also, Access tends to corrupt frequently, so backup, compact and repair need to be done on an frequent basis. 3rd party tools used to exist to automate this task.
As far as performance goes, the data is being processed client side, so you might want to use something like netmeter to watch how much data is going over the wire. The same principle about indexing and avoiding table scans apply to file base dbs as well.
Many good suggestions from other people. Here's my 2 millicents worth. My backend data is on server accessed through a Drive mapping. In my case, the Y drive. Production users get the mapping through a login script using active directory. Then the following scenarios are easily done by batch file:
Develop against local computer by doing a subst command in a batch file
run reports against last nights data by pointing Y to the backup server (read only)
run reports against end of month data by pointing to the right directory
test against specialized scenarios by keeping a special directory
In my environment (average 5 simultaneous users, 1000's of rows, not 10,000's.) corruption has occurred, but it's rare and manageable. Only once in the last several years have we resorted to the previous days backup. We use SQL Server for our higher volume stuff, but it's not as convenient to develop against, probably because we don't have a SQL admin on site.
You might also find some of the answers to this question (how to extract schemas from access) to be useful as well. Once you've extracted a schema using one of the techniques that were suggested you gain a whole range of new options like the ability to use source control on the schemas, as well as being able to easily build "clean" testing environments.
Edit to respond to comment:
There's no easy way to source control an Access database in it's native format, but schema files are just text files like any other. Hence, you can check them in and out of the source control software of your choice for easy version control/rollbacks.
Or course, it relies on you having a series of scripts set up to re-build your database from the schema. Once you do, it's normally fairly trivial to create an option/alternative version that rebuilds it in a different location, allowing you to build test environments from any previous committed version of the schema. I hope that clarifies a bit!
If you want to update the back end MDB schema automatically when you release a new FE to the clients then see Compare'Em http://home.gci.net/~mike-noel/CompareEM-LITE/CompareEM.htm will happily generate the VBA code need to recreate an MDB. Or the code to create the differences between two MDBs so you can do a version upgrade of the already existing BE MDB. It's a bit quirky but works.
I use it all the time.
You need to understand that a shared mdb file for the data is not a robust solution. Microsoft would suggest that SQL Server or some other server based database would be a far better solution and would allow you to use the same access front end. The migration wizard would help you make the changeover if you wanted to go that way.
As another uses pointed out, corruption will occur. It is simply a question of how often, not if.
To understand the performance issues you need to understand that to the server the mdb file with the data in it is simply that, a file. Since no code runs on the server, the server does not understand transactions, record locking etc. It simply knows that there is a file that a bunch of people are trying to read and write simultaniously.
With a database system such as SQL Server, Oracle, DB2. MySQL etc. the database program runs on the server and looks to the server like a single program accessing the database file. It is the database program (running on the server) that handles record locking, transactions, concurrency, logging, data backup/recovery and all the other nice things one wants from a database.
Since a database program designed to run on the server is designed to do that and only that, it can do it far better and more efficently that a program like Access reading an writing a shared file (mdb).
There are two rules for developing against live data
The first rule is . . . never develop
against live data. Not ever.
The second rule is . . .never develop
against live data. Not ever.
You can programatically change the bindings for linked tables, so you can write a macro to change your links when you're deploying a new version.
The application is slow because it's MS Access, and it doesn't like many concurrent users (where many is any number > 1).