>Tried the first approach but got into infinitive loop instead. I am not very comfortable with the second approach.
>
>I guess for now I'll be contend with 2 server hits (but no hits at all afterwards). I hope we will be able to re-design this form to use ui-views instead of the partial views as now. In the latter case the view will only be invoked when clicked on the tab.

How about this (based on Rick's modified service):

        var deferred = null;

        function getMetaData() {
 
            if (deferred !== undefined) {
                return deferred.promise;
            }

            deferred = $q.defer();
            if (service.metaData)
                deferred.resolve(service.metaData);
            else {
                service.inProcess = true;
                $http.get('/api/invoices/metadata')
                    .success(function (data) {
                        service.metaData = data;
                        service.inProcess = false;
                        deferred.resolve(data);

                    })
                    .error(function (data, status, header, config) {
                        deferred.reject(status);
                    });
            }
            return deferred.promise;
        };

(Tried this briefly. Seems to work - i.e. two results; one call to the server.....)