This snippet allows you to define relationships between you backbone models

Backbone.js has_many and belongs_to

$.extend(Backbone.Model.prototype, {
  hasMany: function(collectionName, associationColumn, opts) {
    var parent          = this,
        associationName = (collectionName.substr(0, 1).toLowerCase() + collectionName.substr(1)),
        options         = $.extend({ parentId: 'id' }, opts),
        collection;
    
    this[associationName] = function() {
      collection = window[collectionName].select(function(child) {
        return child.get(associationColumn) == parent.get(options['parentId']);
      });
      return new pimms.model[collectionName](collection);
    };
  },
  
  belongsTo: function(collectionName, associationColumn) {
    var child           = this,
        associationName = (collectionName.substr(0, 1).toLowerCase() + collectionName.substr(1)).replace(/s$/, '');
    
    this[associationName] = function() {
      return window[collectionName].detect(function(parent) {
        return child.get(associationColumn) == parent.get('id');
      });
    };
  }
});