CQRS, decorators and data access?

Question

C++ / C#

In my application, I decided to use the CQRS approach.
The application is written in C# (ASP.NET Core). I use Dapper to access data.
CQRS implemented as follows:
ICommand - command
ICommandHandler - command handler
ICommandDispatcher - finds a handler for a command.
Decorators may be added to command handlers in the future.
The entire application is divided into modules, each of which works with its own database.
Question: how to abstract from a specific database? What about the decorator for transactions? Eg. I will write a factory that will return a database connection. But it turns out that I will ask this factory twice for a connection (in the main handler and in the decorator).