Applying contract constraints

In the previous steps of the Hello, World! tutorial, you built a CorDapp which enabled you to model IOUs on ledger.

Your CorDapp was made up of two elements:

  • An IOUState, representing IOUs on the blockchain.
  • An IOUFlow and IOUFlowResponder flow pair, orchestrating the process of agreeing the creation of an IOU on-ledger.

However, the CorDapp as it stands so far does not impose any constraints on the evolution of IOUs on the blockchain over time. Anyone would be free to create IOUs of any value, between any party.

To rectify this, you must next write a contract to impose rules on how an IOUState can change over time. In turn, this will require some small changes to the flow you defined earlier in Writing the flow.

Start by writing the contract - see Writing the contract.

Once that’s done, you’ll need to make the necessary updates to the flow - see Updating the flow.