No, there isn’t. Remember that the object type determines the input schema: an Employee search has very different input parameters than an Item search, for example. So, varying the object type dynamically would also require dynamically changing what sort of input is delivered to this snap by the snaps upstream from it in the pipeline.
Can you tell me more about the reason for your question? What is the use case where you’d want this field to be dynamically determined? Would you want the expression to evaluate to a value that remains constant for all input documents throughout one execution of the snap, or would you want it to actually be evaluated for every input document?
