Sequelize associations: set[Models] adds new models instead of associating existing ones

I'm using Sequelize and I'm trying to create associations between two different tables, where x.belongsTo(y) and y.hasMany(x). After having done x.setY(yInstance) and y.getXs() it seems only new rows have been added to x and no associations to my already created instances have been created.

var Promise = require("bluebird"),
    Sequelize = require("sequelize");

var sequelize = new Sequelize("Test", "postgres", "password", {
    host: "localhost",
    dialect: "postgres",
    pool: {
        max: 5,
        min: 0,
        idle: 10000
    }
});
var Schedule = sequelize.define("Schedule", {
    website: {
        type: Sequelize.STRING
    }
});
var SiteConfig = sequelize.define("SiteConfig", {
    systemType: {
        type: Sequelize.STRING
    }
});
var Selector = sequelize.define("Selector", {
    type: {
        type: Sequelize.STRING
    },
    content: {
        type: Sequelize.STRING
    }
});
Selector.belongsTo(SiteConfig);
SiteConfig.hasMany(Selector);

var testSchedule = {
    website: "google.com"
};
var testSiteConfig = {
    systemType: "one"
};
var testSelectors = [
    {type: "foo", content: "foo"},
    {type: "foo", content: "bar"}
];



Promise.all([
    Schedule.sync({force: true}),
    SiteConfig.sync({force: true}),
    Selector.sync({force: true})
]).then(function () {
    return Promise.all([
        Schedule.create(testSchedule),
        SiteConfig.create(testSiteConfig),
        Selector.bulkCreate(testSelectors)
    ]);
}).spread(function (schedule, siteConfig, selectors) {
    return Promise.map(selectors, function (selector) {
        return selector.setSiteConfig(siteConfig);
    }).then(function (array) {
        return siteConfig.getSelectors();
    }).each(function (selector) {
        // This is where I expect "foo" and "bar" but instead get null
        console.log("Selector content:", selector.get("content"));
    });
});

I'd expect this code to add a SiteConfigId column to my Selectors so that my siteConfig.getSelectors() would return my testSelectors. How can I achieve this?