feat(ngResource): Add $abort method to objects returned by $resource "class" actions

[arty-name]

$resource "class" actions delegate to $http in a fashion that does not allow to pass timeout promise to individual requests. Hence these individual requests can not be cancelled. This patch adds $abort method to the object returned by $resource "class" actions.

Closes#5612

[IgorMinar]

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[arty-name]

Hi Igor. I've signed Google CLA on 2008-02-29 as Artemy Tregubenko or Artemy Tregoubenko. I suppose the email was atregoubenko@gmail.com, but it could have been me@arty.name as well. I've updated the commit author to be atregoubenko@gmail.com. Should I change it to me@arty.name instead?

[IgorMinar]

please sign the CLA again with the new email address.

however to be honest given the history of aborting/canceling anything promise related, I'm not too hopeful about this PR.

additionally as it stands right now the abort method is associated with the resource instance and not with a request generated by that resource instance, so it's not quite clear which request will be aborted if there are multiple requests in flight.

have you thought about these things?

[arty-name]

I have signed the CLA for atregoubenko@gmail.com

I am not too optimistic about the future of this proposal either, as I have seen the discussions about cancelling, and the current approach of returning promises doesn't suit cancelling very well. However I think this feature is important and I want to try to push for it, even if that means slight architecture change.

I disagree with you that currently the abort method is associated with the resource instance. The deferred that provides the promise for the timeout is scoped to a particular call to a resource action, and is passed to one $http call only, so no matter the amount of parallel requests, only one of them will be aborted. Here's an example:

var resource = $resource(…);
resource.$abort // undefined
var request1 = resource.query(…); // creates deferred1
var request2 = resource.query(…); // creates deferred2
request1.$abort(); // will resolve deferred1 only, but not deferred2, so request2 will continue

[michalgm]

I just want to say thanks for writing this! I spent a long time searching for some way abort specific $resource requests. One question though - is there a way to differentiate in the error handling callback between a request that timed out and a request that was manually aborted?
Thanks again!

[arty-name]

Hi Greg, potentially the promise used to abort or timeout the request may be resolved with different values in each case, and your error callback can check it.

[rainboxx]

@IgorMinar can you take another look at this PR and @arty-name's explanations?

In a current project we have the $resource declaration in a separate factory so we can use it from multiple points in the code. This, however, prevents us to use a promise as the value for timeout, since once resolved we'd had to reset it inconveniently.

The PR seems to be a much better approach.

Thanks.

[IgorMinar]

there is no need for this hunk. if timeout property is set on the httpConfig object, this object is going to be passed into $http which will do exactly what you did here.

[arty-name]

I disagree. There are three options: no property, numeric value or promise value. Latter case I ignore. First case obviously needs handling. However even when numeric value comes in, I cannot just pass it further, as in this case I will not be able to cancel the request. So I have this small code duplication here, but it gives me access to deferred, and it gives me means to cancel the request.

[ghost]

IDK if this is the best implementation or not, but regardless we need to be able to abort individual resource requests. A guy on the Rackspace blog developed some methods to make it possible and simple, but it seems wrong that he had to do all this to get this basic functionality. http://developer.rackspace.com/blog/cancelling-ajax-requests-in-angularjs-applications.html

I need to abort requests if people click too fast on a pager. There are probably countless other times people will want this feature.

[rpocklin]

After much reading into the historical issues and PRs surrounding this topic, i've come to the following conclusion:

1. The ideal solution is non-trivial and still up for debate.
2. ng-resource abstracts $http requests as promises.
3. Promise don't currently support the notion of cancellation, only resolve and reject.

Until an ultimate solution can be resolved we need access to the underlying xhr or $http request. Alternatively just update the documentation to admit this limitation since many people have assumed this feature would just be available.

FWIW i'm defining custom methods on my model object which delegates to $http, which can take the timeout promise directly. I only needed this feature since I am dealing with polling of real-time data but there are many possible use cases.

[arty-name]

Hi. I am closing this PR to explicitly show it's not maintained anymore. Everyone interested are welcome to fork the branch to continue maintenance. Our team has switched to using $http since. I agree with @rpocklin that exposing XHR object for now might be a more flexible solution. I suppose this discussion demonstrates downsides of representing a request object by promise.