How to access the only TRemoteDataModule's instance in my application server

Question

How do I access my Remote Data Module(RDM)'s instance from another unit at runtime? (The RDM is single instance). When I create a normal Data Module descendant Delphi creates a variable for it in the same unit (ex: MyDM: TMyDM), but when I create a RDM's descendant there's no variable.

I'm trying to set the provider of a TClientDataSet created at runtime in another unit to a TDataSetProvider in my RDM, but I can't find a reference to my RDM's instance.

I also tried to do it at design time but while I have no problems to set the connection property of a TSQLQuery from the same unit to a TSQLConnection in that RDM, I wasn't able to set the TClientDataSet's provider, because no providers from the RDM appears in the TClientDataSet's provider list.

Answer 1

First you need to set the RemoteServer property of your client dataset, assign it an instance of TLocalConnection component (which should be placed on your remote data module since you are not using it remotely). The remote data module unit has to be in the uses clause of the unit with the client dataset, of course.

Then you can assign the ProviderName property of your client dataset.

Answer 2

I did some study on TRemoteDataModule and learned that it is dedicated to support COM application servers.

The fact you don´t have a variable to your RDM is because you are not supposed to access it like a regular DM. The application server will instantiate the RDM in response to a remote call, just like any COM application. It will be destroyed when no more references exist to that RDM.

Since the life-cicle of that object depends on the client, not the server, having a reference to it in the server is highly dangerous. You never know when it´s valid or not. Besides, more than one instance will exist, one for each client that is accessing that object in a given moment.

Considering that, I believe is very reasonable to tell you that it´s impossible to access the RDM after it is created to perform the correction you intend to do.

If you really need to put the TDatasetProvider in a different unit, then my best suggestion is to make the RDM look for that provider in some kind of Provider poll service. Doing like this will enable you to find the provider you need everytime a new RDM is instantiated and only when it is instantiated.

In your place I would add a handler to the OnCreate event of the RDM and in that handler I would call a method like TProviderPool.GetProvider. That method would give me a provider and I would assign its name to the ProviderName property of the CDS.