I’m playing with the thought to implement some same game using event sourcing to learn more about it.

Therefore I looked into the documentation of commanded and watched a talk about it. From the documentation and the talk it got pretty clear to me how I should model things that are constrained on one end like a bank withdrawal.

But how could one model transactions that are constrained on both ends?

In the context of the game the first thing came to my mind was a player dropping an item into a chest. The player needs to have the item in his inventory and it needs to fit in the receiving chest.

Currently, the only way I see after reading through commandeds documentation was to do it like this:

1. create a command that moves the item from the inventory to the chest.
2. check if the inventory contains the item in the execute function
3. create the event to move it into the chest
4. create the command that puts the item in the chest from the process manager
5. check if there is enough space in the chest and for this example it is not
6. Fire an event that rolls back the transaction
7. get that one back into the process manager
8. …

But is this atomic? Or could there be a race and the player picked already up another item and doesn’t have room left in his inventory anymore?

Are there possibilities I currently do not see because I have no experience in this field?

Is there a way to get my flow from above atomic? (or is it already?)

Thanks in advance!