gistfile1.js

var Parent = Bookshelf.Model.extend({
	tableName: 'parent',
	child: function() {
		return this.hasOne(Child);
	}
});

var Child = Bookshelf.Model.extend({
	tableName: 'child',
	//this has an attribute parent_id
	parent: function() {
		return this.belongsTo(Parent);
	}
});

Parent.forge({name: "Parent"}).save()
.then(function (parent) {
	// or parent.child().save({name: 'Child'})
	// using .related just throws it on the 
	// parent's .relations hash
	return parent.related('child').save({name: 'Child'});
})
.then(function (child) {
	res.send(child);
});