Upsert() having duplicate error 1062, sqlState 23000 about loopback-connector-mysql HOT 4 CLOSED

var server = require('./server');
var async = require('async');

// Allboard data transfer from old to new
var updateAllBoard = function () {
    server.models.Oldallboards.find({}, function (err, oldServerData) {
        if (err) {
             console.log('%j', err)
            process.exit(1);
        };
        //console.log(oldServerData);

        async.eachSeries(oldServerData, server.models.Allboards.upsert.bind(server.models.Allboards), function (err, result) {
            // With the help of bind we can attach a context to the iterator before
            // passing it to async. Now the function will be executed in its 
            // 'home' server.models.Allboards context.
            if (err)
                console.log(err);
            else
            console.log('Success!');
            process.exit(0);
        });

    });
};

updateAllBoard();

var server = require('./server');
var async = require('async');

// Allboard data transfer from old to new
var updateAllBoard = function () {
    server.models.Oldallboards.find({}, function (err, oldServerData) {
        if (err) {
             console.log('%j', err)
            process.exit(1);
        };
        //console.log(oldServerData);

        async.each(oldServerData, function(data) {
            server.models.Allboards.upsert(data, cb);
        }, function(err) {
            if (err)
                console.log(err);
            else
                console.log('Success!');
            process.exit(0);
        });
    });
};

updateAllBoard();