This Cordapp shows how to trigger a flow with vault update(completion of prior flows) using CordaService & trackby.
In this Cordapp, there are four parties:
- Finance Team: gives payroll order
- Bank Operater: take the order and automatically initiate the money transfer
- PetersonThomas: worker #1 will accept money
- GeorgeJefferson: worker #2 will accept money
There are two states PaymentRequestState & MoneyState, and two flows RequestFlow & PaymentFlow. The business logic looks like the following:
- Finance team put in payroll request to the bank operators
- Bank operator receives the requests and process them without stopping
./greadlew deployNodes
./build/node/runnodes
if you have any questions during setup, please go to https://docs.corda.net/getting-set-up.html for detailed setup instructions.
Once all four nodes are started up, in Financeteam's node shell, run:
flow start RequestFlowInitiator amount: 500, towhom: GeorgeJefferson
As a result, we can check for the payment at GeorgeJefferson's node shell by running:
run vaultQuery contractStateType: net.corda.examples.autopayroll.states.MoneyState
We will see that George Jefferson received a MoneyState with amount $500.
Behind the scenes, upon the completion of RequestFlow, a request state is stored at Bank operator's vault. The CordaService vault listener picks up the update and calls the paymentFlow automatically to send a moneyState to the designed reciever.
The CordaService that triggers the flow is defined in AutoPaymentService.kt. The CordaService annotation is used by Corda to find any services that should be created on startup. In order for a flow to be startable by a service, the flow must be annotated with @StartableByService. An example is given in PaymentFlow.kt.
You probably have noticed that paymentFlow is not tagged with @StartableByRPC like flows normally are. That is, it will not show up in the node shell's flow list. The reason is that paymentflow is a completely automated process that does not need any external interactions, so it is ok to be "not-been-seen" from the RPC.
That said, CordaService broadly opens up the probabilities of writing automated flows and fast responding Cordapps!