John W. Colby
jcolby at ColbyConsulting.com
Thu Mar 20 19:36:00 CST 2003
Eric,
If you have unhandled errors causing globals to lose their value you have
big problems. Unhandled errors pretty much reset the whole damned world,
not just "global" variables.
John W. Colby
Colby Consulting
www.ColbyConsulting.com
-----Original Message-----
From: accessd-admin at databaseadvisors.com
[mailto:accessd-admin at databaseadvisors.com]On Behalf Of StaRKeY
Sent: Thursday, March 20, 2003 4:30 PM
To: accessd at databaseadvisors.com
Subject: RE: [AccessD] Using Global Connections
First of all, I am not against globals but I think there are a couple of
things to bare in mind:
1) - kept open connections could slow down traffic in general, usually only
if your app is used by a lot of
people/connections
2) - what is the max. amount of open connections allowed?
3) - globals can loose their value in case an unhandled error occurs
4) - no Mark, in a LOT of cases you are NOT the only programmer over time...
Last but not least, I've seen many different Access applications and to be
honest, whenever I was asked to come fix or upgrade an app. I've never
really cared about how the job was done unless it actually was
creating/being a problem.
My two cents..
Eric
-----Original Message-----
From: accessd-admin at databaseadvisors.com
[mailto:accessd-admin at databaseadvisors.com]On Behalf Of Mark L. Breen
Sent: donderdag 20 maart 2003 22:22
To: accessd at databaseadvisors.com
Subject: Re: [AccessD] Using Global Connections
Hello John,
I am glad to hear that I am on the right track anyway. The reason that I
asked the question was that I noticed a few people referring to globals
recently. Also, I have been reading a bit about them and the author was
complaining about globals. But, as we are both agreed, for a global
constant connection, there is a lot of upside and very little downside to
using one. I had considered using a class and setting properties, bit
again, that is only really complictating it further. However, I could make
it a read only class, and that would have some benefit, or I could do as you
do and use a function.
Based on the fact that I am the programmer, nobody else is going to mess
with my global variable, I can probably continue to use a normal global and
pass it around.
I am reading with interest your migration to .net, I am about to start the
same thing myself in the next few weeks.
If I have anything to post, I will.
I think that everybody on the list should let each other know if we come
across any good reading material, especially online / free stuff.
Thanks to all for the feedback on the globals.
Best Regards
Mark L. Breen
Solution Providers
Ireland
----- Original Message -----
From: "John W. Colby" <jcolby at colbyconsulting.com>
To: <accessd at databaseadvisors.com>
Sent: Saturday, March 15, 2003 5:03 PM
Subject: RE: [AccessD] Using Global Connections
> Mark,
>
> I also use globals for the db connection. This is a case where the
> connection is specific, a penalty is paid for creating / deleting it, and
it
> is needed all over the app. The connection is not something that is going
> to be updated (written to) by pieces of the application, it is going to be
> created once and then used all over. That is a good candidate for a
global.
>
>
> Globals tend to cause problems when they are *updated* from all over the
> place, and the reason is that is quite difficult to track down who is
doing
> the updating when it is incorrectly updated. If for example a serial port
> is opened and closed by 10 different functions, one function tries to use
> the serial port and it is closed. Who closed it? It's supposed to be
> opened, but some process closed it unexpectedly. These kinds of problems
> can be a real bear to track down and fix.
>
> It becomes a bigger problem if the system is written and maintained by a
> team of programmers where nobody knows the whole story. Globals by
> definition are available to anyone at any time.
>
> Scope exists for a reason. If a variable is only used by a specific
> function, then it's variables have no business being global to the program
> (or even the module). If a variable is only used by code inside an
instance
> of a class but needs to be accessed by several functions inside the class,
> then it should be defined inside the class (in the header) as a PRIVATE
> variable. Thus only code inside the class can modify the variable. If a
> variable needs to be shared by many functions inside of a module, but only
> these functions modify the variable, then the variable should be PRIVATE
to
> that module. By making any of these variables truly Global to the
project,
> you end up with things being (able to be) set by code that has no business
> setting the variable.
>
> On the other hand, if as in your example, a database connection is needed,
> and a function calls a function which calls a function, which needs that
> connection, why pass the connection through 3 functions that don't even
need
> the connection simply so that the fourth function that does need it can
have
> access to the connection?
>
> In a case like this, I tend to make the connection a private variable
inside
> a module, with a function that initializes the variable when the db opens,
> and then define a function that READS the connection variable and returns
> the value. This in effect makes it read only. Anyone can call the
function
> that gets the value, but since the variable is PRIVATE to the module, no
one
> outside the module can write to it.
>
> John W. Colby
> Colby Consulting
> www.ColbyConsulting.com
>
> -----Original Message-----
> From: accessd-admin at databaseadvisors.com
> [mailto:accessd-admin at databaseadvisors.com]On Behalf Of Mark L. Breen
> Sent: Friday, March 14, 2003 12:37 PM
> To: accessd at databaseadvisors.com
> Subject: Re: [AccessD] Using Global Connctions
>
>
> Hello All,
>
> I was not aware that a previous debate (sounds a little heated) had been
> already carried out. Sorry for duplicating the discussion.
>
> In the last few emails, Marcus was the only one that explicitly stated
that
> he likes the idea of using Globals for a db connection.
>
> So leaving aside passing around an order nunber or a customer id as a
global
> (which I would never even consider), what do you guys do to hand around a
> database connection? Do you use Globals or do you make the connction each
> time or do you use some kind of class. Any sample code would be
interesting
> to read.
>
> What I do is have the following code in a module
>
> ' This will be the global connection that we will share, we open it once
> only and share it throughout the applications life
> Global gccnn As New ADODB.Connection
> Global Const gcstrConStr As String = "Provider=SQLOLEDB.1;Integrated
> Security=SSPI;Persist Security Info=False;Initial Catalog=spps40;Data
> Source=PC1"
>
>
> and then in the first form_load I have
>
> ' Give it a connect string
> gccnn.ConnectionString = gcstrConStr
>
> ' And make the connection
> gccnn.Open
>
>
>
> What do you guys think of this strategy, should I use a class to pass it
> around. And if I am not using a class, do you think that it is a little
bit
> untidy or is downright bad practice.
>
> Again, I am just curious what the rest of the world is doing in their
apps.
>
> Thanks
>
> Mark
>
>
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>
>
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