Contract Method not returning value

Question

I have a contract :

pragma solidity ^0.4.2;

import "Owned.sol";
contract SGBFactory is Owned {

    event SGBUpdate(uint sbgID, bool isCreated, string message); // isCreated = true means created, else means deleted

    string public ownerType;

    struct SGB {
        uint id;
        string latitude;
        string longitude;
        uint minBal; // should be in Wei since Solidity doesn't support floating points as of now
        string ownerType;
        uint capacity; //should also be in grams due to the same reasons as above
        address owner;
        uint fixedUnitCostPerTransaction;
    }

    SGB[] public sgbCollection;

    function SGBCreator() {
        ownerType = "COMMUNITY";
    }

    function addSGB(
        string lat,
        string lon,
        uint minBalReq,
        uint maxCapacity,
        address ownerAccount,
        uint fixedCost
    ) onlyOwner {
        uint sgbID = sgbCollection.length++; //note the postfix operator here
        sgbCollection[sgbID] = SGB(sgbID, lat, lon, minBalReq, ownerType, maxCapacity, ownerAccount, fixedCost);
          // fire up an event here
        SGBUpdate(sgbID,true, "A new SGB is created!!");
    }

    function getSGB(uint sgbid) returns (uint sbgID, string lat, string lon, uint minBal,string ownerType) {
        return(
            sgbCollection[sgbid].id,
            sgbCollection[sgbid].latitude,
            sgbCollection[sgbid].longitude,
            sgbCollection[sgbid].minBal,
            sgbCollection[sgbid].ownerType
        );
    }

    // uint maxCapacity, address owner, uint fixedCost
    // sgbCollection[sgbid].capacity,sgbCollection[sgbid].owner,sgbCollection[sgbid].fixedUnitCostPerTransaction
}

It is deployed in my private Ethereum chain. I can call getSGB() method from Truffle console and it returns value successfully.

I used the following mechanism in Truffle console:

var contract = SGBFactory.deployed();
contract.getSGB.call(1, {from: "0x85ded4eae096d15de9bee720a6e91eb28603a7e6"}, function(err, res) {
    console.log(res);
});

But when I call the same method from JS file, the method returns nothing, nor there is an error message.

SGBWatcher.js

var accounts;
var coinbase_account;

function getSGBFromFactory() {
    var sgbAdderContract = SGBFactory.deployed();
    console.log(coinbase_account);
    sgbAdderContract.getSGB.call(0, {from: coinbase_account }, function(err, res) {
        if (err != null)
            console.log(err);
        else
            console.log(res);
    });
}

window.onload = function() {
    web3.eth.getAccounts(function(err, accs) {
        if (err != null) {
            alert("There was an error fetching your accounts.");
            console.log(err);
            return;
        }

       if (accs.length == 0) {
           alert("Couldn't get any accounts! Make sure your Ethereum client is configured correctly.");
           return;
       }

       accounts = accs;
       coinbase_account = accounts[0];
   });
}

What could be the issue here? (I already have two SGBs added in the contract, so the indexes 0 and 1 as parameter should be fine.)

Answer 1

1. You send 0 as argument in

   sgbAdderContract.getSGB.call(0,{from: coinbase_account },function(err,res){ if(err != null) console.log(err); else console.log(res); });

   Does identifier exist?

2. Ensure you realy call getSGBFromFactory() from your JS code

Answer 2

Not certain this is it, but possibly.

In Truffle 0.3.x you might consider changing the contract instantiation to a callback.

Instead of

var sgbAdderContract = SGBFactory.deployed(); console.log(coinbase_account)

Consider

var sgbAdderContact;
SGBFactory.deployed(function(instance) { 
  sgbAdderContract = instance; 
  console.log(sgbAdderContract); 
});

Answer 3

sgbCollection(uint _idx); already exists as the getter function of SGB[] public sgbCollection;. It will return the struct SGB element values as an array in the order of the struct. Your front end only needs to map those to something meaningful if required. So getSGB is not actually required. If however there is some need of the named return parameters, then you should modify the function as constant as there is no state changes and so no need to create a transaction.

function getSGB(uint sgbid) constant returns (uint sbgID, string lat, string lon, uint minBal,string ownerType) {...}

Your JS then simply becomes sgbAdderContract.getSGB(0) or using the accessor sgbAdderContract.sgbCollection(0)

Answer 4

The solution was :

sgbAdderContract.getSGB.call(0,{from : coinbase_account}).**then**(function(result){
//do somethiing
}).catch(function(e){
// error
});