Contract SDK - Record Player Maintenance

If you're familiar with record players you probably know how difficult it is to make sure that they run in pristine condition, especially if it's a collectible.

This cordapp simulates how you could model the process of a limited edition record player (the cordagraf) that is manufactured and issued to specific dealers, and those dealers are the only entities that can service those record players after the fact and report stats back to the manufacturer about how the players are being used.

Record Players are issued as LinearStates and are updated by dealers, that act functionally as the only entity that can update the RecordPlayer state.

Using the Contract SDK

The contract sdk is a series of Annotations that you can use in your corda contracts. It's great for putting together cleaner contract code and writing it faster.

This repository demonstrates how you can configure and use it in your own projects.

Configuration is essentially three small steps:

• adding maven { url 'https://software.r3.com/artifactory/corda-lib-dev' } to repositories.gradle
• adding compile "com.r3.corda.lib.contracts:contract-sdk:0.9-SNAPSHOT" to the build.gradle file of your contract module in your cordapp
• adding the annotations to your apps!

To show how convenient this can be, here's an example demonstrating how to configure a simple issuance command with one output and no inputs.

// note the annotations here from the Contracts SDK
@RequireNumberOfStatesOnInput(value = 0)
@RequireNumberOfStatesOnOutput(value = 1)
class Issue implements Commands {}

If you've written contracts before you might be used to outlining the verify method, applying a conditional for issuance commands and configuring a lot of the same verification for contract inputs. This removes the need for those tools.

Take a look at the small RecordPlayerContract sample in this repository to see how this works in practice.

Sources

If you're looking to find more information on record players specifically, I included some sources for how we modeled record players in the state class.

• You can find much more information on the contract sdk on github here
• The notes on the number of turns in a record player cartridge coil was sourced from here
• The info on other aspects of amplifiers was sourced from here