Utilizing $resource within a promise sequence to correct the deferred anti-pattern

Question

Utilizing $resource within a promise sequence to correct the deferred anti-pattern

One challenge I encountered was that when making multiple nearly simultaneous calls to a service method that retrieves a list of project types using $resource, each call generated a new request instead of utilizing the same response/promise/data. After doing some research, I came across a solution which revealed an issue with creating a redundant $q.defer() called the deferred anti-pattern.

The initial code worked well as long as the calls were spaced out sufficiently. However, the consecutive calls did not share the projectTypes data. Additionally, any failed requests to retrieve project types would trigger dfr.reject(), which could be caught by .catch() in the controller.

angular.module('projects')
.factory('projectService', function(notificationService){

    var shared = {};

    var projectResource = $resource(baseApiPath + 'projects', {}, {
        ...,
        getProjectTypes: {
            method: 'GET',
            url: baseApiPath + 'projects/types'
        },
        ...
    });

    var loadProjectTypes = function(){
        var dfr = $q.defer();

        if(shared.projectTypes){
            dfr.resolve(shared.projectTypes);
        }
        else {
            projectResource.getProjectTypes(null,
            function(response){
                shared.projectTypes = response.result.projectTypes;
                dfr.resolve(response);
            },
            function(errResponse){
                console.error(errResponse);
                notificationService.setNotification('error', errResponse.data.messages[0]);
                dfr.reject(errResponse);
            });
        }
        return dfr.promise;
    };

    return {
        shared: shared,
        project: projectResource,
        loadProjectTypes: loadProjectTypes
    };
});

To optimize this code and eliminate unnecessary use of $q.defer(), I made some adjustments:

...
    var projectResource = $resource(baseApiPath + 'projects', {}, {
        ...,
        getProjectTypes: {
            method: 'GET',
            url: baseApiPath + 'projects/types',
            isArray: true,
            transformResponse: function(response){
                return JSON.parse(response).result.projectTypes;
            }
        },
        ...
    });

    var loadProjectTypes = function(){
        return shared.projectTypes || (shared.projectTypes = projectResource.getProjectTypes());
    };
...

Despite these improvements, there were still issues with error handling and promise chaining. In the original code, errors were appropriately handled in the catch statement of the controller. However, the updated version lacked similar error propagation. Attempting to replace dfr.reject() and dfr.resolve() with $q.reject() and $q.resolve() respectively proved ineffective.

This raised the question of whether the original implementation actually fell into the category of an anti-pattern or if it was a valid way of utilizing $q.defer(). As I delved deeper into seeking a solution, I realized the need for a consistent approach where the same promise/data was returned regardless of when the method was called. Ensuring proper error handling throughout the promise chain involving $resource posed a challenge yet to be resolved.

Continuing my search for a comprehensive solution, I outlined three main requirements:

Requirement 1: Enable multiple method calls while only triggering a single API request to update all callers with the same data.

Requirement 2: Allow usage of the method result as actual data per the promise specification. For example,

var myStuff = service.loadStuff()

should set myStuff to "stuff".

Requirement 3: Facilitate promise chaining so that any errors within the chain can be managed by a single catch statement at the end. The goal is to have robust error handling across different chains and catches within the application.

javascript angularjs promise angular-resource

Answer 1

Answer №1

It seems that speaking about your problems often leads you to find the solution.

Requirement 1: Ensure only one request is made per method call, which is resolved by fixing the anti-pattern. This fix will always return the $resource result by either caching it or returning and caching it simultaneously.

var loadProjectTypes = function(){
    return shared.projectTypes || (shared.projectTypes = projectResource.getProjectTypes());
};

Requirement 2: Enable using the service method as a promise so that the value of a $scope variable can be set directly to the result of loadProjectTypes(). The updated method allows for simply stating

$scope.theTypes = projectService.loadProjectTypes()

, which automatically fills in the list of types when available, aligning with the promise specification.

Requirement 3: Allow for chaining multiple $resource calls and catching their errors with a single .catch(). By utilizing the $promise of the result from loadProjectTypes within $q.all(), any errors can be caught in a desired catch block.

$q.all([
    ...,
    projectService.loadProjectTypes().$promise,
    ...
])
.then(function(response){
    // handling project types from response[n]
})
.catch(function(errResponse){
    // capturing any errors here
});

Any catches placed at different points will function similarly. Using a .catch() whenever loadProjectTypes() is invoked ensures error handling. Each loader has the flexibility to handle API failures in its unique way. This allows for tailored responses based on where the data is being loaded.

The structures of my service, directive, and controller now appear as follows:

// Code samples used for AngularJS modules and components.

Since the loadProjectTypes (or any other load_____ method) stores the types internally in the originating service, there's no need for additional storage in controllers.

projectService.shared.projectTypes

is universally accessible throughout the application. If all services store results internally, controllers might not require significant logic unless specific view-related actions are necessary. Controllers primarily manage entire pages or modals, while directives and services handle most information and logic.

~~The question remains open for better solutions.~~ While Jack A.'s suggestion addresses Requirement 1 and potentially 2 and 3, it introduces verbosity to the 'load___' methods. Despite solving some challenges, it can lead to redundant or complex code in practice given slight differences across multiple methods. It's an effective approach but may complicate maintainability in real-world scenarios.

UPDATE (GOTCHA):

After implementing this pattern for a few days, it streamlined our workflow effectively. However, a notable issue emerged when using a method like loadProjectTypes outside of $q.all().

If the load method is used individually in a controller:

// Code snippet in the controller's initialization section
loadProjectTypes()
.$promise
.then(...)
.catch(...);

Upon returning to the controller, issues arise when refreshing - triggering an "undefined .then" error. Subsequent invocations of loadProjectTypes() do not include a $promise; instead, they only return cached project type data. Although baffling, this behavior necessitates handling such scenarios.

return shared.projectTypes || (shared.projectTypes = projectResource.getProjectTypes());

A quick resolution involves incorporating loadProjectTypes().$promise within a $q.all() block:

// Placing this code near the beginning of the controller
$q.all([
    loadProjectTypes().$promise
])
.then(...)
.catch(...);

In situations requiring loading a single item, employing a solitary set within $q.all() eliminates potential issues. While manageable, this adjustment ensures seamless operation in varying contexts, preventing unexpected errors.

Answer 2

It seems that speaking about your problems often leads you to find the solution.

Requirement 1: Ensure only one request is made per method call, which is resolved by fixing the anti-pattern. This fix will always return the $resource result by either caching it or returning and caching it simultaneously.

var loadProjectTypes = function(){
    return shared.projectTypes || (shared.projectTypes = projectResource.getProjectTypes());
};

Requirement 2: Enable using the service method as a promise so that the value of a $scope variable can be set directly to the result of loadProjectTypes(). The updated method allows for simply stating

$scope.theTypes = projectService.loadProjectTypes()

, which automatically fills in the list of types when available, aligning with the promise specification.

Requirement 3: Allow for chaining multiple $resource calls and catching their errors with a single .catch(). By utilizing the $promise of the result from loadProjectTypes within $q.all(), any errors can be caught in a desired catch block.

$q.all([
    ...,
    projectService.loadProjectTypes().$promise,
    ...
])
.then(function(response){
    // handling project types from response[n]
})
.catch(function(errResponse){
    // capturing any errors here
});

Any catches placed at different points will function similarly. Using a .catch() whenever loadProjectTypes() is invoked ensures error handling. Each loader has the flexibility to handle API failures in its unique way. This allows for tailored responses based on where the data is being loaded.

The structures of my service, directive, and controller now appear as follows:

// Code samples used for AngularJS modules and components.

Since the loadProjectTypes (or any other load_____ method) stores the types internally in the originating service, there's no need for additional storage in controllers.

projectService.shared.projectTypes

is universally accessible throughout the application. If all services store results internally, controllers might not require significant logic unless specific view-related actions are necessary. Controllers primarily manage entire pages or modals, while directives and services handle most information and logic.

~~The question remains open for better solutions.~~ While Jack A.'s suggestion addresses Requirement 1 and potentially 2 and 3, it introduces verbosity to the 'load___' methods. Despite solving some challenges, it can lead to redundant or complex code in practice given slight differences across multiple methods. It's an effective approach but may complicate maintainability in real-world scenarios.

UPDATE (GOTCHA):

After implementing this pattern for a few days, it streamlined our workflow effectively. However, a notable issue emerged when using a method like loadProjectTypes outside of $q.all().

If the load method is used individually in a controller:

// Code snippet in the controller's initialization section
loadProjectTypes()
.$promise
.then(...)
.catch(...);

Upon returning to the controller, issues arise when refreshing - triggering an "undefined .then" error. Subsequent invocations of loadProjectTypes() do not include a $promise; instead, they only return cached project type data. Although baffling, this behavior necessitates handling such scenarios.

return shared.projectTypes || (shared.projectTypes = projectResource.getProjectTypes());

A quick resolution involves incorporating loadProjectTypes().$promise within a $q.all() block:

// Placing this code near the beginning of the controller
$q.all([
    loadProjectTypes().$promise
])
.then(...)
.catch(...);

In situations requiring loading a single item, employing a solitary set within $q.all() eliminates potential issues. While manageable, this adjustment ensures seamless operation in varying contexts, preventing unexpected errors.

Answer 3

Answer №2

I had previously written something quite similar to this, but with a few distinct differences:

My approach involved creating the promise only when the data was already present in the cache and simply returning the native promise whenever an actual request was made.
I introduced a third state for situations where a request for the resource was already in progress.

A more concise representation of the code is shown below:

module.factory("templateService", function ($templateCache, $q, $http) {
    var requests = {};
    return {
        getTemplate: function retrieveTemplate(key, url) {
            var data = $templateCache.get(key);
            
            if (data) {
                var deferred = $q.defer();
                var promise = deferred.promise;
                deferred.resolve({ data: data });
                return promise;
            }
            else if (requests[url]) {
                return requests[url];
            }
            else {
                var req = $http.get(url);
                requests[url] = req;
                req.success(function (data) {
                    delete requests[url];
                    $templateCache.put(key, data);
                });
                return req;
            }
        },
    };
});

Answer 4

I had previously written something quite similar to this, but with a few distinct differences:

My approach involved creating the promise only when the data was already present in the cache and simply returning the native promise whenever an actual request was made.
I introduced a third state for situations where a request for the resource was already in progress.

A more concise representation of the code is shown below:

module.factory("templateService", function ($templateCache, $q, $http) {
    var requests = {};
    return {
        getTemplate: function retrieveTemplate(key, url) {
            var data = $templateCache.get(key);
            
            if (data) {
                var deferred = $q.defer();
                var promise = deferred.promise;
                deferred.resolve({ data: data });
                return promise;
            }
            else if (requests[url]) {
                return requests[url];
            }
            else {
                var req = $http.get(url);
                requests[url] = req;
                req.success(function (data) {
                    delete requests[url];
                    $templateCache.put(key, data);
                });
                return req;
            }
        },
    };
});

Utilizing $resource within a promise sequence to correct the deferred anti-pattern

Answer №1

Answer №2

Similar questions

Testing with mount in React Enzyme, the setState method does not function correctly

What is the best way to guide the user to a different page with PHP once the preventDefault() function in jQuery has been utilized on a

Sending basic HTML from Express.jsSending simple HTML content from an Express.js

DiscordJS bot using Typescript experiences audio playback issues that halt after a short period of time

Tips on effectively storing extra object properties across all entries in a MongoDB document group

Tips for transferring parameters between AJAX requests

Guidance that utilizes the scope of a specific instance

Evaluating Jasmine unit tests using promises with odata

Enhancing your Selenium test case strategies for better performance

Error message indicates failure of switch case, resulting in invalid output of

Populate object values dynamically through function invocations

What is the most efficient method for clearing the innerHTML when dealing with dynamic content?

What are some alternative solutions when functional component props, state, or store are not being updated within a function?

mdDialog select an item based on its unique identification number

Modifying an HTML attribute dynamically in D3 by evaluating its existing value

Solving filtering issues within React using a combination of conditions

How to utilize the Ember generate command for an addon

Monitoring changes in an array of objects using AngularJS's $watch function

The text entered in the textbox vanishes after I press the submit button

Tips for configuring formik values