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 Operator: takes the order and automatically initiates the money transfer
- PetersonThomas: worker #1 who accepts the money
- GeorgeJefferson: worker #2 who accepts the money
There are two states PaymentRequestState and MoneyState, and two flows RequestFlow & PaymentFlow. The business logic looks like the following:
- Finance team puts in payroll request to the bank operators
- Bank operator receives the requests and processes them without stopping
Set up for CorDapp development
./gradlew clean build deployNodes
./build/node/runnodes
Once all four nodes are started up, in Finance Team's node shell, run:
flow start RequestFlowInitiator amount: 500, towhom: GeorgeJefferson
As a result, we can check for the payment in GeorgeJefferson's node shell by running:
run vaultQuery contractStateType: net.corda.samples.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 designated receiver.
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 means it will not show up in the node shell's flow list. The reason for that is because 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!