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I am having some trouble getting a retry function to work and was hoping for some assistance. I have a $resource that I want to have called until a success condition occurs or the maximum retries has been exceeded.
The issue I seem to be running into is that within my retry function I am calling another promise and that is where the condition would be checked. I could get the code to function as intended by removing the added promise and creating a default success condition after a few retries but I cannot figure out how to correctly add the new promise call into the function.
resource is a stand-in for an Angular $resource which returns a $promise
My code is as follows:
resource.$promise.then(function (response) {
return keepTrying(state, 5);
}).then(function (response) {
}).catch(function (err) {
console.log(err);
});
And the keepTrying function:
function keepTrying(state, maxRetries, deferred) {
deferred = deferred || $q.defer();
resource.$promise.then(function (response) {
success = response;
});
if (success) {
return deferred.resolve(success);
} else if (maxRetries > 0) {
setTimeout(function () {
keepTrying(state, maxRetries - 1, deferred);
}, 1000);
} else if (maxRetries === 0) {
deferred.reject('Maximum retries exceeded');
}
return deferred.promise;
}
454
The problem with your attempt is that you are not re-querying the resource, but using the promise for an already-queried resource over and over.
What you need to do is use a function that will (a) initiate the query, and (b) return the promise for that initiated query. Something like this:
function () { return $resource.get().$promise; }
Then you can pass it into something like this, that will do the retries.
function retryAction(action, numTries) {
return $q.when()
.then(action)
.catch(function (error) {
if (numTries <= 0) {
throw error;
}
return retryAction(action, numTries - 1);
});
}
Here's how you would start this off:
retryAction(function () { return $resource.get().$promise; }, 5)
.then(function (result) {
// do something with result
});
One nice thing about this approach is that even if the function that you pass to it throws an error upon invoking it, or doesn't return a promise at all, the retry functionality and the returning of the result via a resolved promise will still work.
Example
163
You can implement a retryOperation function that returns a new promise upon error up to a maximum retry count thats passed as an argument:
function retryOperation(retryCount) {
var count = 0;
function success(result) {
return result;
}
function error(result) {
++count;
if (count <= retryCount)
return $resource(...).query().$promise.then(success, error);
throw 'max retries reached';
}
return $resource(...).query().$promise.then(success, error);
}
Usage
retryOperation(3).then(
function success(result) {
// done!
},
function error(reason) {
alert(reason);
});
var app = angular.module('app', []);
app.controller('ctrl', function($q) {
function retryOperation(count) {
var retryCount = 0;
function operation() {
var deferred = $q.defer();
deferred.reject('failed');
return deferred.promise;
}
function success(result) {
return result;
}
function error(result) {
++retryCount;
if (retryCount <= count) {
alert('retrying ' + retryCount);
return operation().then(success, error);
}
throw 'maximum retries reached';
}
return operation().then(success, error);
}
retryOperation(3).then(
function success(result) {
alert('done');
},
function error(result) {
alert(result);
});
});<html>
<head>
<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.23/angular.min.js"></script>
</head>
<body ng-app="app" ng-controller="ctrl">
<input type="text" ng-model="name" />{{name}}
</body>
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