I have a business case where I am developing a simple search UI, I would like to link it to our SQL Server as the performance is pretty fast when I test it. My plan is to create a few linked tables and create a tidy search form for each linked table (different datasets).
UPDATE, here is a better description of my plan
I have a single user ID / Password that I want to use in each ODBC connection on 4 linked SQL tables (its considered an APP ID at my company, the PW never changes). There will be 4 forms that link to each of the tables and each user will have their own accde db with a launch file that places a copy on the users profile drive and opens it from there. This allows each user to have their own copy of the accde file and everyone to have only one "launch" file.
This search UI, will have upwards of 2000 users, who knows how many actually executing a search at any given time. Security is not a concern as it is a DB on an internal SQL Server which is managed by our IT area. The end users are all internal employees.
Will using just the one ID potentially lock out my APP ID and cause major issues?
Will MS Acess no longer be a major choke point if each user has their own accde file?
Thank you and sorry that my first version of this question was not 100% clear, thanks!
So, I figured I would circle back and post up what I did. While providing a singular app ID with a File DSN in a shared location for the Access Front end would have worked, it was ultimately not the most stable solution.
Since I am in a large corporate environment, my options were extremely limited. That said, I was able to have a read only role added to the database I manage, sourced an "Active Directory Group" that had the membership I needed (as a bonus, the membership was managed at the corporate level!) and I added the AD Group to the read only role.
I then created a File DSN using windows authentication security, placed it in a shared folder location (where I also added the same AD Group to a read only role on the folder) and emailed out a shortcut to a simple batch file launcher that copies an ACCDE database to the users profile drive.
The accde houses all the necessary search forms, logic and linked tables needed for the end user. I even build in a back door that crashes out the end users (with a warning) with a simple file rename. The front end runs surprisingly fast with the test group of 100 individuals and is rolling out to 500 next week.
Viola. Hope this helps someone trying to do something similar.
I am not sure what the correct forum is for a question like this, so if it would go better on a different one could you move it there please?
I have split my database into a front and back-end database. The front end is using linked tables which are linked to the back-end real tables. If a user changes something in a table on the front-end database, the changes are carried over to the backend database.
Why is this and how can I prevent this from happening? Is there a way to change the settings to make the database read only? Whether it's through VBA or not, I would accept either answer.
That's a feature, not a bug. You're using a linked table, it's linked.
If you want a separate table, make a separate table, and make some ETL (extract/transform/load) process to keep the two tables in sync as needed, accordingly with whatever business rules you need to implement.
If your Access DB is connecting to SQL Server via SQL authentication, you could have the SQL user on the SQL Server side only authorized to SELECT, and denied UPDATE, DELETE and INSERT permissions. Expect errors on the Access side when the linked table is modified then.
So, I've got an access database that I want to open.
I can see the querys/forms/tables exist but when I want to open them it tells me
"X:[...]\database.mdb" is not a valid path. Of course, because this is my computer. So when I select them to relink them in the wizard, I select the current database file and it just tells me, that the query/form/table doesn't exist in there and I should check the name.
But I am in that database and I can see those forms exist. The database itself is just around 1mb, is there something msissing maybe? Don't think so, huh.
It looks like your Access database project has been split into Front-End and Back-End databases.
This is normal practice for an Access database project of any significant size.
It seems you have the front-end database - this is the one containing the forms etc. Yes, it will list the tables but all those tables are just links. The underlying data is not in this front-end database, but in the back-end.
If your tables are shown with a small arrow then these are linked tables and a sure sign you have a front-end database:
When you fire up the Linked Table Wizard you need to browse to the back-end database, not the current database. If you cannot locate the back-end or no longer have it, then basically, you have no data. Your front-end database may be of little value on its own.
I'm considering undertaking a project to migrate a very large MS Access application to a new system based on SQL Server. The existing system is essentially an ERP application with a couple of dozen users, all sharing the Access database over the network. The database has around 300 tables and lots of messy VBA code. This system is beginning to break down (actually, it's amazing it has worked as long as it has).
Due to the size and complexity of the Access application, a 'big bang' approach is not really feasible. It seems sensible to rope off chunks of functionality and migrate them piecemeal to the new system. During the migration process, which I expect to take several months, there may be a need for both databases to be in operation and be able to query and modify data in both systems.
I have considered using something like the ADO.NET Entity Framework to implement a data abstraction layer to handle this, but as far as I can tell, the Entity Framework has no Access provider.
Does my approach seem reasonable? What other strategies have people used to accomplish similar goals?
You may find that the main problem is using the MS Access JET engine as the backend. I'm assuming that you do have an Access FE (frontend) with all objects except tables, and a BE (backend - tables only).
You may find that migrating the data to SQL Server, and linking the Access FE to that, would help alleviate problems immediately.
Then, if you don't want to continue to use MS Access as the FE, you could consider breaking it up into 'modules', and redesign modules one by one using a separate development platform.
We faced a similar situation a few years ago, but we knew from the beginning that we'll have to swich one day to SQL SERVER, so the whole code was written to work from an Access client to both Access AND SQL server databases.
The idea of having a 'one-step' migration to SQL server is certainly the easier way to manage this on the database side, and there are many tools for that. But, depending on the way your client app talks to the database, your code might then not work properly. If, for example, your code includes a lot of SQL instructions (or generates them on the fly by, for example, adding filters to SELECT instructions), your syntax might not be 'SQL server' compatible: access wildcards, dates, functions, will not work on SQL server.
In addition to this, and as said by #mjv, the other drawback of a one time switch to MS SQL is that you will inheritate many of the problems from the original database: wrong or inapropriate field names, inapropriate primary/foreign key policies, hidden one-to-many relations that you'd like to implement in the new database model, etc.
I'll propose here some principles and rules to implement a 'soft transition' solution, which clearly best fits you. Just to say that it's not going to be easy, but it's definitely very interesting, paticularly when dealing with 300 tables! Lucky you!
I assume here that yo have the ability to update the client code, and you'd prefer to keep at all times the same client interface. It is of course possible to have at transition time two different interfaces, one for each database, but this will be very confusing for the users, and a permanent source of frustration for them.
According to me, the best solution strongly depend on:
The original connection technology,
and the way data is managed in your
client's code: Access linked tables,
ODBC, ADODB, recordset, local
tables, forms recordsources, batch
updating, etc.
The possibilities to split your
tables and your app in 'mostly
independant' modules.
And you will not spare the following mandatory activities:
setup up of a transfer
procedure from Access database to SQL server. You
can use already existing tools (The
access upsizing wizard is very poor,
so do not hesitate to buy a real
one, like SSW or EMS SQL Manager,
very powerfull) or build your own
one with Visual Basic. If your plan
is to make some changes in Data
Definition, you'll definitely have
to write some code. Keep in mind
that you will run this code
maaaaaany times, so make sure that
it includes all time-saving
instructions that will allow you to
restart the process from the start
as many times as you want. You will
have to choose between 2 basic data
import strategies when importing data:
a - DELETE existing record, then INSERT imported record
b - UPDATE existing record from imported record
If you plan to switch to new Primary\foreign key types, you'll have to keep track of old identifiers in your new database model during the transition period. Do not hesitate to switch to GUID Primary Keys at this stage, especially if the plan is to replicate data on multiple sites one of these days.
This transfer procedure will be divided in modules corresponding to the 'logical' modules defined previously, and you should be able to run any of these modules independantly (keeping of course in mind that they'll probably have to be implemented in a specific order, where the 'customers' module has to run before the 'invoicing' module).
implement in your client's code the possibility to connect to both original ms-access database and new MS SQL server. Ideally, you should be able to manage from within your code both connections for displaying and validating data.
This possibility will be implemented by modules, where you will have, for each of them, a 'trial period', ie the possibility to choose at testing time between access connection and sql connection when using the module. Once testing is done and complete, the module can then be run in exclusive SQL server mode.
During the transfer period, that can last a few months, you will have to manage programatically the database constraints that exist between 'SQL server' modules and 'Access' modules. Going back to our customers/invoicing example, the customers module will be first switched to MS SQL. Before the Invoicing module can be switched, you'll have to implement programmatically the one to many relations between Customers and Invoices, where each of the tables will be in a different database. Such a constraint can be implemented on the Invoice form by populating the Customers combobox with the Customers recordset from the SQL server.
My proposal is to build your modules following your database model, allways beginning with the 'one' tables or your 'one-to-many' relations: basic lists like 'Units', 'Currencies', 'Countries', shall be switched first. You'll have a first 'hands on' experience in writting data transfer code, and managing a second connection in your client interface. You'll be then able to 'go up' in your database model, switching the 'products' and 'customers' tables (where units, countries and currencies are foreign keys) to the new server.
Good luck!
I would second the suggestion to upsize the back end to SQL Server as step 1.
I would never go to the suggested Step 2, though (i.e., replacing the Access front end with something else). I would instead suggest investing the effort in fixing the flaws of the schema, and adjusting the Access app to work with the new schema.
Obviously, it is never the case that everything just works hunky dory when you upsize -- some things that were previously quite fast will be dogs, and some things that were previously quite slow will be fast. And I've found that it is often the case that the problems are very often not where you anticipate that they will be. You can only figure out what needs to be fixed by testing.
Basically, anything that works poorly gets re-architected, or moved entirely server-side.
Leverage the investment in the existing Access app rather than tossing all that out and starting from scratch. Access is a fine front end for a SQL Server back end as long as you don't assume it's going to work just the same way as it would with a Jet/ACE back end.
...thinking out loud... I think this may work.
I appears that the complexity of the application resides in the various VBA modules rather than the database table/schema themselves. A possible migration path could therefore be to first migrate the data storage to SQL server, exactly as-is, as follow:
prevent any change to the data for a few hours
duplicate all tables to the SQL server; be sure to create the same indexes as well.
create linked tables to ODBC Source pointing to the newly created tables on SQL Server
these tables should have the very same name as the original tables (which therefore may require being renamed, say with a leading underscore, for possible reference).
Now, the application can be restarted and should be using the SQL tables rather than the Access tables. All logic should work as previously (right...), possible slowness to be expected, depending on the distance between the two machines.
All the above could be tested in about a day's work or so; the most tedious being the creation of the tables on SQL server (much of that can be automated, I'm sure). The next most tedious task is to assert that the application effectively works as previously, but with its storage on SQL.
EDIT: As suggested by a comment, I should stress that there is a [fair ?] possibility that the application would not readily work so smoothly under SQL server back-end, and could require weeks of hard work in testing and fixing. However, and unless some of these difficulties can be anticipated because of insight into the application not expressed in the question, I propose that attempting the "As-is" migration to SQL Server should be considered; after all, it may just work with minimal effort, and if it doesn't, we'd know this very quickly. This is therefore a hi-return, low risk proposal...
The main advantage sought with this approach is that there will be a single storage during the [as the OP expects] longer period during which the old Access application will co-exist with the new application.
The drawback of this approach, is that, at least at first, the schema of original database is reproduced verbatim, i.e. including some of its known quirks and legacy-herited idiosyncrasies. These schema issues (and the underlying application logic) can be in time corrected, but this is of course less easy than if the new application starts ab initio, with its own, separate, storage, and distinct schema.
After the storage is moved to SQL server, the most used and/or the most independent modules of the Access application can be re-written in the new application, and as significant portions of the original application is ported, effective usage, by select beta testers or by actual users can start to be switched to the new application.
Possibly, some kind of screen-scraping based logic or some other system could be used to produce an hybrid application which would provide the end users with a comprehensive application, which sometimes work from new logic, and sometimes from the original MS-Access program.
I am developing an Adobe AIR application which stores data locally using a SQLite database.
At any time, I want the end user to synchronize his/her local data to a central MySQL database.
Any tips, advice for getting this right?
Performance and stability is the key (besides security ;))
I can think of a couple of ways:
Periodically, Dump your MySQL database and create a new SQLite database from the dump. You can then serve the SQLite database (SQLite databases are contained in a single file) for your users client to download and replace the current database.
Create a diff script that generates the necessary statements to bring the current database up to speed (various INSERT, UPDATE and DELETE statements). To do this, you must record the time of each change continuously in your database (the time of creation and update for each row, and keep a history of deleted rows).
User's client will download the diff file (a text file of the various statements) and apply it on the local database.
Both approaches have their own pros and cons - by dumping the entire database, you make sure all the data gets through. It is also much easier than creating the diff, however it might put more load on the server, depending on how often does the database gets updated between dumps.
On the other hand, diffing between the database will give you just the data that changed (hopefully), but it is more open to logical errors. It will incur an additional overhead on the client as well, since it will have to create/update all the necessary records instead of just copying a file.
If you're just sync'ing from the server to client, Eran's solution should work.
If you're just sync'ing from the client to the server, just reverse it.
If you're sync'ing both ways, have fun. You'll at minimum probably want to keep change logs, and you'll need to figure out how to deal with conflicts.