AngularJS Deferred $http

app.controllers.project.js

angular
  .module('app.controllers.project', [
    'app.models.project'
  ])
  .controller('app.controllers.project', [
    '$routeParams',
    '$scope',
    'project',
    function($params, $scope, project) {
      $scope.project = project;
    }
  ])
;

app.models.project.js

angular
  .module('app.models.project', [
    'app.models.todoLists'
  ])
  .factory('app.models.project', [
    '$q',
    '$http',
    'app.models.todoLists',
    function($q, $http, TodoLists) {
      var Project = function(properties) {
        angular.extend(this, properties);
      };

      var data;
      var deferred;

      Project.prototype.todoLists = function() {
        if (!deferred) {
          deferred = $q.defer();

          $http
            .get('/api/projects/' + this.id + '/todolists')
            .then(function(response) {
              return response.data;
            })
            .then(function(lists) {
              data = lists;

              deferred.resolve(data);
            })
          ;
        } else if (data) {
          deferred.resolve(data);
        }

        return deferred.promise;
      };

      return Project;
    }
  ])
;