Is there any way a CorDapp can ask a Notary if a state has been consumed prior to using it in a Transaction?
Background:
I am testing FungibleToken’s that point to EvolvableTokenType’s. Eventually the EvolvableTokenType changes and holders of the tokens that are not Participants of the EvolvableTokenType end up with states in their vault that have been unknowingly consumed. When they try to execute a transaction involving these states the Notary will refuse to sign because it knows the states have been consumed.
I have written flows that will contact a Participant and request the missing state(s). However it would be more efficient if I could first ask the Notary if I need to do that (i.e. if the state hasn’t been consumed I don’t need to ask a participant for an update).
You could do this a couple ways.
For example, in your vault query, you could simply make sure to filter on StateStatus = UNCONSUMED. That's one way you can ensure this works the way you expect and you never get a state that won't fit your criteria.
check out this section of the docs on vaultQuery : https://docs.corda.net/docs/corda-os/4.7/api-vault-query.html#querycriteria-interface
The other way I'd recommend that might also work is just to include this filter in your contract verification for the transaction, but doing it at the flow level just catches the problem sooner rather than later.