🚀 go-pugleaf

Mark Stephens <marks@stconsult.co.nz> wrote in article
<01bd8792$dfb1fa40$081260cb@actrix.gen.nz.actrix.gen.nz>...
> Hi. I have a fairly complex application that is currently two-tier, ie
> database sits on a server and the client application talks to it through
> BDE on the client.
> 
> I want to move the application to a 3-tier structure, and I've examined
the
> sample Delphi programs in some depth and tried to delve my way through
the
> on-line help about COM, multi-tier and all that. I understand the
> principles but I still don't understand the technicalities of it.
> 
> I have some questions about it:
> 1. My application currently dynamically constructs SQL code into TQuery
> objects, where the tables, selection criteria and sort order are all
> potentially dynamic. How can I do this using TClientDataSet - it appears
to
> have no way to send SQL to the data broker?
> 2. How do you create the server so it is registered? I tried creating a
> server, created a few datasets, a provider etc, all as on the sample, but
I
> couldn't find out how to create the text library that appears to be
> automatically generated in the sample.
> 
> Are there any further resources out there about how to construct 3-tier
> database structures - it would seem to me the demand for such
applications
> is going to dramatically increase in the not too distant future, and
> there's not much information about how to do it.
> 

No kidding there isn't much information on it! We found that out soon
enough. However, now that I know what I do, looking back in the D3 help
pages, it is all explained - just not in layman's terms.
There is an example on how to set up the application server (do a search in
the help under 'Application Server'). The server is registered when you
execute it for the first time.
The client sends the SQL, via the TRemoteServer (or TMidasConnection) to a
TQuery object on the server. This TQuery is 'made visible' to the client
(that's the simplest way to explain it) - how to make it visible is
explained in the help. The TRemoteServer has a property call AppServer
which points to this interface.

Once you have the architecture in place, it's all pretty simple.
Good luck - you may need it :-)

- Graeme Vincent

In article <01bd8792$dfb1fa40$081260cb@actrix.gen.nz.actrix.gen.nz>,
  "Mark Stephens" <marks@stconsult.co.nz> wrote:
>
> Hi. I have a fairly complex application that is currently two-tier, ie
> database sits on a server and the client application talks to it through
> BDE on the client.
>
> I want to move the application to a 3-tier structure, and I've examined the
> sample Delphi programs in some depth and tried to delve my way through the
> on-line help about COM, multi-tier and all that. I understand the
> principles but I still don't understand the technicalities of it.
>
> I have some questions about it:
> 1. My application currently dynamically constructs SQL code into TQuery
> objects, where the tables, selection criteria and sort order are all
> potentially dynamic. How can I do this using TClientDataSet - it appears to
> have no way to send SQL to the data broker?
> 2. How do you create the server so it is registered? I tried creating a
> server, created a few datasets, a provider etc, all as on the sample, but I
> couldn't find out how to create the text library that appears to be
> automatically generated in the sample.
>
> Are there any further resources out there about how to construct 3-tier
> database structures - it would seem to me the demand for such applications
> is going to dramatically increase in the not too distant future, and
> there's not much information about how to do it.
>
> Thanks,
> Mark Stephens
> Manager, Systems Development
> Sullivan Thomson Limited
> Wellington, New Zealand
>

One of the ideas of the multi tier architecture is that the client end
doesn't need to know anything about the database structure used
by the database server, so sending dynamically created SQL isn't
the sort of thing you're supposed to do.  That's not to say you can't
of course.  One way to do it is to export a function from your application
server which sets the SQL property of a TQuery to the string passed
into the function.  Then open the dataset and hey presto.  There's
an example of this on the Inprise web site in their developer support
area.

Hope that helps

Cliff Evans

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