Promise Chains in angularjs - angularjs

Question

I am uploading attachments using rest api in SharePoint 2013,for this I need to call upload attachment method on synchronous.
Because If I call upload attachment method asynchronous I am getting 409 conflict error.
How to chain promise objects in for loop.i.e I want to call second attachment method in first attachment success and so on..
Please help me in best approach of chaining of promises in for loop.
Common method for saving attachments:
var saveFileAngularJS = function (file, url) {
var deferred = $q.defer();
getFileBuffer(file).then(function (fileArrBuffer) {
$http({
method: 'POST',
url: baseUrl + url,
headers: {
'Accept': 'application/json;odata=verbose',
'Content-Type': undefined,
'X-RequestDigest': jQuery("#__REQUESTDIGEST").val()
},
data: new Uint8Array(fileArrBuffer),
transformRequest: []
}).then(function successCallback(data) {
deferred.resolve(data);
alert('Successfully saved.', data);
}, function errorCallback(error) {
deferred.reject(error);
alert('Failed to save!!!.', error);
});
});
return deferred.promise;
};
Method calling :
for (var i = 0; i < $scope.files.length; i++) {
var file = $scope.files[i]._file;
var response = lssDealService.insertAttachment(transactionId, file);
}
var insertAttachment = function (dealId, file) {
var attachmentUrl = listEndPoint + "/GetByTitle('TransactionList')/GetItemById(" + dealId + ")/AttachmentFiles/add(FileName='" + file.name + "')";
return baseService.saveFile(file, attachmentUrl);
};
Insert attachment will call SaveFile method.
I want to run this for loop sequentially, once the loop has been completed I need to process all promises and display success message to user.
Please help me to writing the chaining promises in effective way.

Answer 1

Lets say you have the attachements as an array,
function uploadMyAttachements() {
return myAttachements.reduce(function(promise, attachment) {
return promise.then(function () {
return upload(attachment);
})
.then(function(result) {
console.log('RESULT FOR LAST UPLOAD', result);
});
}, Promise.resolve());
}
function upload(attachment) {
//upload the attachment to sharepoint
//and return a promise here
}
uploadMyAttachements().catch(function(err) {
//if anything in the promise chain fails
//it stops then and there and CATCHED here
});
Now whats happening here, using the Array.reduce, we create a chain of promises like shown below
upload(0).then(handleResult_0).upload(1).then(handleResult_1)....
and it execute one by one as you expected

Answer 2

Throwing my 2 pennies:
$scope.attachments = []; //modified via binding.
function uploadAttachments(){
//Reduce the files array into a promise array with the uploadOne method
//then return the promise when every promise has been resolved or one has rejected.
return $q.all($scope.attachments.reduce(uploadOne, []));
}
function uploadOne(file){
//Upload one, return promise. Use $http or $resource.
}
//Note - a more advanced way of doing this would be to send the files as batch (one
//$http post) as FormData. There are some good wrappers for angular.
$scope.upload = function(){
uploadAttachments().then(function(results){
//Array of results
}).catch(function(e){
//Error handler
});
}