How to get data back from an action ?

Hello,

Would it be possible to get data back from an action (out of the question EO_MESSAGE & ET_FAILED_KEY )?

For example we got an order with order positions and we need a "function" to e.g. count all positions. Because of Performance the function should not be processed each time the order is changed, read or a position is added. Instead the function should be processed only if it was called explicitly.

Is it possible to create a kind of action which is actually counting all entries and export the number of them?

How to mark a parameter in is_parameters as exporting?

Is this just done by (naming-) convention?

What is the preferred way to have “methods” with returning/exporting values?

Regards,

Lorenz