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Maybe if there's an invoke for it, what resource are you trying to check for?

Is there a way to get the ressources that are already in the stack?

Well if there already in the stack then preview will know about them? I'm a bit confused as to what your asking for here.

actually I am doing a preview of a program already ran, there is new code in this pulumi program.
So I would like to know if a specific resource was already there in the stack. I need to know this in the program itself

If you put the code that needs that resource to exist inside an ID.Apply it will only run if the ID resolves