Hyperledger Composer Playground Tutorial

Step Four: Adding a model file

As you can see, we’re in the Define tab right now, this tab is where you create and edit the files that make up a business network definition, before deploying them and testing them using the Test tab.

As we selected an empty business network template, we need to modify the template files provided. The first step is to update the model file. Model files define the assets, participants, transactions, and events in our business network.

For more information on our modeling language, check our documentation.

1. Click the Model file to view it.
2. Delete the lines of code in the model file and replace it with this:

/**
 * My commodity trading network
 */
namespace org.example.mynetwork
asset Commodity identified by tradingSymbol {
    o String tradingSymbol
    o String description
    o String mainExchange
    o Double quantity
    --> Trader owner
}
participant Trader identified by tradeId {
    o String tradeId
    o String firstName
    o String lastName
}
transaction Trade {
    --> Commodity commodity
    --> Trader newOwner
}

1. This domain model defines a single asset type Commodity and single participant type Trader and a single transaction type Trade that is used to modify the owner of a commodity.

Step Five: Adding a transaction processor script file

Now that the domain model has been defined, we can define the transaction logic for the business network. Composer expresses the logic for a business network using JavaScript functions. These functions are automatically executed when a transaction is submitted for processing.

For more information on writing transaction processor functions, check our documentation.

1. Click the Add a file button.
2. Click the Script file and click Add.
3. Delete the lines of code in the script file and replace it with the following code:

/**
 * Track the trade of a commodity from one trader to another
 * @param {org.example.mynetwork.Trade} trade - the trade to be processed
 * @transaction
 */
async function tradeCommodity(trade) {
    trade.commodity.owner = trade.newOwner;
    let assetRegistry = await getAssetRegistry('org.example.mynetwork.Commodity');
    await assetRegistry.update(trade.commodity);
}

This function simply changes the owner property on a commodity based on the newOwner property on an incoming Trade transaction. It then persists the modified Commodity back into the asset registry, used to store Commodity instances.

Step Six: Access control

Access control files define the access control rules for business networks. Our network is simple, so the default access control file doesn’t need editing. The basic file gives the current participant networkAdmin full access to business network and system-level operations.

While you can have multiple model or script files, you can only have one access control file in any business network.

For more information on access control files, check our documentation.

Step Seven: Deploying the updated business network

Now that we have model, script, and access control files, we need to deploy and test our business network.

Click Deploy changes to upgrade the business network.

NOTE: If you are using playground locally and connecting to a real Fabric please refer to the additional notes at the bottom of the tutorial.

Step Eight: Testing the business network definition

Next, we need to test our business network by creating some participants (in this case Traders), creating an asset (a Commodity), and then using our Trade transaction to change the ownership of the Commodity.

Click the Test tab to get started.

Step Nine: Creating participants

The first thing we should add to our business network is two participants.

1. Ensure that you have the Trader tab selected on the left, and click Create New Participant in the upper right.
2. What you can see is the data structure of a Trader participant. We want some easily recognizable data, so delete the code that’s there and paste the following:

{
  "$class": "org.example.mynetwork.Trader",
  "tradeId": "TRADER1",
  "firstName": "Jenny",
  "lastName": "Jones"
}

{
  "$class": "org.example.mynetwork.Trader",
  "tradeId": "TRADER2",
  "firstName": "Amy",
  "lastName": "Williams"
}

{
  "$class": "org.example.mynetwork.Commodity",
  "tradingSymbol": "ABC",
  "description": "Test commodity",
  "mainExchange": "Euronext",
  "quantity": 72.297,
  "owner": "resource:org.example.mynetwork.Trader#TRADER1"
}

{
  "$class": "org.example.mynetwork.Trade",
  "commodity": "resource:org.example.mynetwork.Commodity#ABC",
  "newOwner": "resource:org.example.mynetwork.Trader#TRADER2"
}

Logging out of the business network

Now that transactions have successfully run, we should log out of the business network, ending up at the My Business Network screen where we started.

1. In the upper-right of the screen is a button labelled admin. This lists your current identity, to log out, click admin to open the dropdown menu, and click My Business Networks.

Deploying a Business Network to a real Fabric.

Using Playground locally, you can use connections to “Web Browser” which works in the browser local storage, or you can use Connections to a real Fabric usually in a group called “hlfv1”

If you are connecting to a real Fabric, then you will likely have already created a Card for an identity with PeerAdmin and ChannelAdmin roles – this is often called PeerAdmin. This is the card that you use to Deploy and Update your network with Composer.

When you are deploying your network to a real Fabric there are additional fields to complete before you can click the Deploy button – you need to supply the details of the Network Administrator.