Web3J: callback to retreive public struct

Question

I am trying to access data stored in a contract from web3. I have managed to do so with a custom get function, however from what I have read online, every public variable has a built in get and set function created by Solidity. I also understood that it has somethign to do with callbacks, but I am not sure how to implement it in my js code. Here is what I have done to get my data so far:

Solidity Contract

contract OrganizationObject {

    struct organizationDetails {
        string name; 
        string vat; 
        string headquarterAddress;
    }

    organizationDetails public details;

    address[] public staff;

    function OrganizationObject (string name, string vat, string headquarterAddress){
        details.name = name;
        details.vat = vat;
        details.headquarterAddress = headquarterAddress;
    }

    function getDetails() public constant returns (bytes32[], string, string, string){
        return (order, details.name, details.vat, details.headquarterAddress);
    }

    function addStaff(address x){
        staff.push(x);
    }
}

web3

app.post('/api/getOrganisationDetails', stormpath.authenticationRequired, function(req, res){
    var rawString = req.user.customData;
    var stringJson = JSON.stringify(rawString);
    var customData = JSON.parse(stringJson);
    var web3 = new Web3();

    web3.setProvider(new web3.providers.HttpProvider(customData.ethereum_provider));
    var address = req.body.address;

    // creation of contract object
    var MyContract = web3.eth.contract(abi.abiOrganisationObject).at(address);
    var details = MyContract.getDetails();
    console.log(details);
    res.end(details).status(200);
});

I think the better solution would be to use the getter function from solidity, I have tried like this:

app.post('/api/getOrganisationDetails', stormpath.authenticationRequired, function(req, res){
    var rawString = req.user.customData;
    var stringJson = JSON.stringify(rawString);
    var customData = JSON.parse(stringJson);
    var web3 = new Web3();

    web3.setProvider(new web3.providers.HttpProvider(customData.ethereum_provider));
    var address = req.body.address;

    // creation of contract object
    var MyContract = web3.eth.contract(abi.abiOrganisationObject).at(address);
    var details = MyContract.details();
    console.log(details);
    res.end(details).status(200);
});

But it seems to want an argument in the MyContract.details(), which i assume is a callback. What should I do to be able to access the data stored inside MyContract.details ?

Answer 1

You can't directly read a struct from web3, you need to break it down in a constant function that return each attribute like you did in getDetails() .

Moreover I would advice to make asynchronous call to the contract and use call() for a constant function.

• Asynchronous call is safer in my opinion
• call() will explicitly send a call (executed in the VM) rather than a sendTransaction (that must be mined)

So in your case, that should look like this:

var MyContract = web3.eth.contract(abi.abiOrganisationObject).at(address);
MyContract.getDetails.call().then(function(error, result){
    if (!error) {
        console.log(result); // details
        var order = web3.toAscii(result[0]);
        var name               = result[1];
        var vat                = result[2];
        var headquarterAddress = result[3];

    } else {
        console.log(error); 
    }
}));