How can I prevent Delphi from throwing exception when 2 transactions are open (using FireDac component and FireBird dbms)?

Question

I built an Web API with Delphi using FireDac and an HTTPServer component: The application is using a dbms powered by firebird.

Everything was working fine until I the moment I started to simulate multiple requests to the same API endpoint. This is causing internal server exceptions reporting that a second trasaction is being opened when there are already a transaction opened.

I know that all connections are being closed after being used and objects are being destroyed in order to prevent memory leaks but I couldn't understand why do the application triggers the exception.

Any help or toughs that might drive me to a solution?

Answer 1

Multiple requests will be processed concurrently by the HTTP server.

So if two clients try to access the same resource (URL) at the same time, the server will need two sets of database connections and data access components.

If your application uses distinct objects - one set per client - and does this in a thread safe way, both connection should work fine.

However if you use only one datamodule to serve all incoming HTTP requests, proper serialization is required. It does not help to close connections after use, the connections must be used only from one thread at a time.

So to understand the potential reason of the error, more information about the actual design of your server is needed.