Use Polymorphic models in 1:M relations

poly_1:M.js

var Club = Backbone.AssociatedModel.extend({
    relations:[{
        type:Backbone.Many,
        key:'members',
        relatedModel:function (relation, attributes) {
            return function (attrs, options) {
                if (_.isArray(attrs.dependents)) {
                    return new Employee(attrs);
                }

                return new Dependent(attrs);
            }
        }
    }],
    defaults:{
        name:"",
        members:[]
    },
    urlRoot:'/club'
});

var club = new Club({
    name:"Club X"
});

club.set({
    members: [{
        fname: "John",
        lname: "Smith",
        age: 21,
        sex: "M",
        dependents: [child1, child2]
    }, {
        fname: "Edgar",
        lname: "Smith",
        sex: "M",
        relationship: "P"
    }]
});

console.log(club.get('members[0]') instanceof Employee); //true
console.log(club.get('members[1]') instanceof Dependent)//true;

Contributed by @dak