Creating instance with an association in Sequelize

First of all you need to setup the relations in both ways, like this:

// Set up the models
var User = sequelize.define('User', {});
var Login = sequelize.define('Login', {});

// Set the correct associations
User.hasMany(Login, {})
Login.belongsTo(User, {});

Then, you need to properly get the instances returned by the promises:

// Create the instances
User.create({}).then(function(newUser) {
    // now you can use newUser acessors to create the login
    return newUser.createLogin({});
).then(function(newLogin){
    // newLogin
}).catch(function(error){
    // error
});

Assuming you have the right association between users and login, you can just create a user including a login:

User.create({
   name: "name",
   Login: {...}
},{
   include: Login
})

you can find more information here: http://docs.sequelizejs.com/manual/tutorial/associations.html#creating-with-associations