Hyperledger Composer How to Update Existing Assets

Question

I am trying to create a simple hyperledger chaincode in composer that updates the asset associated  if it exists, else creates a new asset.

My code:

function createTransaction(tx) {
    var NS = 'org.acme.ra';
    var factory = getFactory();
    var loanToUpdate

//returns all assets 
  return getAssetRegistry(NS + '.Loan')
      .then(function(assetRegistry){
       return assetRegistry.exists(tx.loanNum);  
      })
      .then(function(exists){
          if (exists) {
                  return getAssetRegistry(NS + '.Loan')                         
                      .then(function(assetRegistry2){                            
                          loanToUpdate =  assetRegistry2.get(tx.loanNum)
                          loanToUpdate.balance = tx.transAmount;
                          return assetRegistry2
                      })
                      .then(function(updateAssetRegistry){
                          return updateAssetRegistry.update(loanToUpdate)//broken right here
                  })
          } 
          else {
                  return getAssetRegistry(NS + '.Loan')
                      .then(function(assetRegistry2){
                       var newLoan =factory.newResource(NS,'Loan',tx.loanNum);
                          newLoan.balance = tx.transAmount;                         
                          return assetRegistry2.add(newLoan);
                      })                             
          }
      })       

Answer 1

get on an asset registry returns a promise, so the line  loanToUpdate = assetRegistry2.get(tx.loanNum) needs to be part of the promise chain and so you need a .then block to process the returned value before you can update it.