I need to upload some data to server. Just before doing so, I fetch an entity that this data should be bounded to(simple relationship). If there is no such entity, I want to create it then and continue uploading process. The problem, though, is that if there are too many requests, all requests will end up faster than creation of the entity, thus many entities will be created. The solution is to dispatch the block of code synchronously, but on a different thread. How do I do this?
dispatch_sync(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH,0), ^{
PFQuery *query = [PFQuery queryWithClassName:#"FileOwner"];
[query whereKey:#"identifier" equalTo:#"ABCDEFG"];
PFObject *fileOwner = [query getFirstObject];
if(fileOwner){
[self continueUploadingData:data completionHandler:completionBlock];
}
else{
PFObject *newFileOwner = [PFObject objectWithClassName:#"FileOwner"];
newPhotoOwner[#"identifier"] = #"ABCDEFG";
[newPhotoOwner saveInBackgroundWithBlock:^(BOOL succeeded, NSError *error) {
if(succeeded)[self continueUploadingData:data completionHandler:completionBlock];
}];
}
});
This works, but obviously blocks the main thread. I can't use detachSelector: toTarget: withObject: because I have more than one argument.
The general purpose advice that will help here is to build the atomic functions with methods that take completion blocks (like parse's, maybe like your continueUploading method).
In this case, we need a function that will look for an object, return it if it's found, or create and return it if it's not found, all asynch...
- (void)findOrCreateFileOwnerWithIdentifier:(NSString *)identifier completion:(void (^)(PFObject *, NSError *))completion {
PFQuery *query = [PFQuery queryWithClassName:#"FileOwner"];
[query whereKey:#"identifier" equalTo:identifier];
[query getFirstObjectInBackgroundWithBlock:^(PFObject *object, NSError *error) {
if (object) {
return completion(object, nil);
} else {
PFObject *newFileOwner = [PFObject objectWithClassName:#"FileOwner"];
newFileOwner[#"identifier"] = identifier;
[newFileOwner saveInBackgroundWithBlock:completion];
}
}];
}
Now you can say...
[self findOrCreateFileOwnerWithIdentifier:#"ABCDEFG" completion:^(PFObject *fileOwner, NSError *error) {
if (!error) {
[self continueUploadingData:data completionHandler:completionBlock];
} else {
// handle error... probably pass it to completionBlock
// not shown because the OP code doesn't show how the block is declared
}
}];
Related
I am using this query to find users, it works but it just shows me the first user. I want it to show me the user with the text of an UITextField.
How can I do that ?
(I have a textfield and there I type in a name and then it should show the parsed users with the name)
PFQuery *query = [PFUser query];
NSArray *users = [query findObjects];
userQuerys.text = users[0][#"username"];
Thanks very much
This code will fetch you all the PFUsers in which username is equal to the name parameter:
- (void)searchUsersNamed:(NSString *)name withCompletion:(void (^)(NSArray *users))completionBlock {
PFQuery *query = [PFUser query];
[query whereKey:#"username" equalTo:name];
[query findObjectsInBackgroundWithBlock:^(NSArray *users, NSError *error) {
if (!error) {
// we found users with that username
// run the completion block with the users.
// making sure the completion block exists
if (completionBlock) {
completionBlock(users);
}
} else {
// log details of the failure
NSLog(#"Error: %# %#", error, [error description]);
}
}];
}
An example, if you need to update the UI with the result, for example, a table:
- (void)someMethod {
// we will grab a weak reference of self to perform
// work inside the completion block
__weak ThisViewController *weakSelf = self;
//replace ThisViewController with the correct self class
[self searchUsersNamed:#"Phillipp" withCompletion:^(NSArray *users) {
//perform non-UI related logic here.
//set the found users inside the array used by the
//tableView datasource. again, just an example.
weakSelf.users = users;
[[NSOperationQueue mainQueue] addOperationWithBlock:^{
//pefrorm any UI updates only
//for example, update a table
[weakSelf.tableView reloadData];
}];
}];
}
A small note: the completionBlock here wont run if there is an error, but it will run even if no users were found, so you gotta treat that (if needed. in this example, it was not needed).
Avoid running non-UI related logic on that mainQueue method, you might lock the Main thread, and that`s bad user experience.
I am having trouble saving a PFRelation I have this code:
//set up the query
PFQuery *query = [PFQuery queryWithClassName:#"messageBank"];
[query whereKey:#"username" equalTo:name];
__weak User *weakSelf = self;
[query getFirstObjectInBackgroundWithBlock:^(PFObject *object, NSError *error) {
if(error) {
NSLog(#"No such user");
handler(NO, error,NO,NO);
}
else{
[weakSelf.friendsRelation addObject:object];
[weakSelf.friends addObject:object];
//save in the background
[weakSelf.messageBank saveInBackgroundWithBlock:^(BOOL succeeded, NSError *error) {
if(error) {
NSLog(#"Save error");
}
else {
NSLog(#"no error");
}
}];
handler(YES,nil,NO,NO); //no errors
//so the friend is added to the friends array, all we need to do is reload the table data don't need to init the array again, the relation is also added to the relation item so don't need to init that again
}
}];//end block
My code finds the messageBank object fine but it won't save it to the PFRelation friends. It doesn't even attempt to call [weakSelf.messageBank saveInBackgroundWithBlock.... weakSelf.messageBank is the local PFObject and weakSelf.friends is it's PFRelation. Anyone have any ideas what could be going wrong here? If I have a PFRelation in class A is it okay to have pointers in that relation to other objects in class A? Does it need to be in a different class? Any help would be much appreciated!!!
Here's a cleaned up version of the code that fetches an object and adds to its relation, and saves it...
PFQuery *query = [PFQuery queryWithClassName:#"messageBank"]; // by convention class names should be capital MessageBank, but using yours
[query whereKey:#"username" equalTo:name]; // better form is self.name assuming it is an attribute of self
[query getFirstObjectInBackgroundWithBlock:^(PFObject *object, NSError *error) {
if (!error) {
// see note below about weakSelf
// assume self is a PFObject subclass with two relations
// (and generated setters) called friendsRelation and friends
[self.friendsRelation addObject:object];
[self.friends addObject:object];
// notice we save self here. that's who changed in the two preceding lines
[self saveInBackgroundWithBlock:^(BOOL succeeded, NSError *error) {
if(!error) {
// success
} else {
// handle error
}
}];
} else {
// handle error
}
}];
Please notice that there's no need to declare a __weak copy of the self pointer (though, there's no harm in it). That idiom is used to avoid a retain cycle between self and the block's owner. You need it only when self is the blocks owner (directly or indirectly). This isn't the case with parse's completion blocks.
I have a code snippet that will update information in the Parse database. I set up an action so that when the information is saved, it gets updated in the background. The function is being executed, but it's not saving anything on the database. its going through the function, but no changes are being saved. The changed values are inside a text field and a switch.
- (IBAction)save:(id)sender {
NSLog(#"classnameinsave %#", self.productTitleField.text);
PFQuery *query = [PFQuery queryWithClassName:self.className];
[query getObjectInBackgroundWithId:self.productId block:^(PFObject *object, NSError *error) {
NSLog(#"inside getObjectsInBackgroundWithId function");
NSLog(#"priceinsave %#", object[#"price"]);
object[#"title"] = self.productTitleField.text;
object[#"price"] = self.priceField;
object[#"quantity"] = self.quantityField;
object[#"show"] = self.show;
[object saveInBackgroundWithBlock:^(BOOL succeeded, NSError *error) {
if(succeeded){
NSLog(#"Succeeded in Saving");
}else if(error){
NSLog(#"Error with saving changes %#", error);
}
}];
}];
}
Most likely this happened because the PFObject you're looking for doesn't even exist! You forgot to add the if statement for verifying if the object exists. Also, I understand you want to make it as dynamic as possible by having the class name based on a UILabel, but please don't do this, this doesn't make sense at all. Replace your code with this:
PFQuery *query = [PFQuery queryWithClassName:#"ClassName"];
[query getObjectInBackgroundWithId:self.productId block:^(PFObject *object, NSError *error) {
if(object){
//Do everything here :)
}else{
//Display an UIAlertView to the user?
NSLog(error);
}
}];
Note: You should add the if statement, however it's not necessary.
Best regards,
how can I ignore new fetching if one is already running. Here is one example of my code:
So if i call [self getParticipants] how to make sure to ignore if already running. The only solution I've got is to create BOOL property "inMiddleOfFetching" but I dont want to create anther BOOL property just for this. Is there a better solution?
- (void)getParticipants {
PFQuery *participantsQuery = [self.participantsRelation query];
[participantsQuery includeKey:#"client"];
[participantsQuery findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) {
if (objects)
self.participants = objects;
}];
}
This is not simpler but it is better, you can use bolts to create a single task for the query, this way if it is called multiple times it will only run once but all calls will return the value at the same time.
Something like this:
#property BFTask* task;
- (BFTask *)getParticipants {
if (!_task) {
PFQuery *participantsQuery = [self.participantsRelation query];
[participantsQuery includeKey:#"client"];
_task = [participantsQuery findObjectsInBackground];
}
return _task;
}
Then to get the result:
[[self getParticipants] continueWithBlock:^id(BFTask *task) {
if(!task.error){
self.participants = task.result;
}
_task = nil; //if you want to run the query again in the future
return nil;
}];
I have a class on Parse.com called "Hospital", which has a few rows on it. I want to query all the rows in this object, and then selectively delete some of them.
I figure I need to cycle through the object, gathering the objectIDs, and then look at the row associated with each ID to figure out which ones should be deleted. I can't find how to do this anywhere. I've tried this:
PFQuery *query = [PFQuery queryWithClassName:#"Hospital"];
But this returns an object with 0 objects inside it, when there is definitely a row in the Parse.com database.
Once I get this part working, and get objectIDs, it seems I can delete a row with the following:
PFObject *testObject = [PFObject objectWithoutDataWithClassName:#"Hospital" objectId:#"NMZ8gLj3RE"];
[testObject deleteInBackgroundWithBlock:^(BOOL succeeded, NSError *error) {
if (succeeded){
NSLog(#"BOOOOOM"); // this is my function to refresh the data
} else {
NSLog(#"DELETE ERRIR");
}
}];
PFQuery *query = [PFQuery queryWithClassName:#"Hospital"];
[query findObjectsInBackgroundWithBlock:^(NSArray *hospitals, NSError *error) {
if (!error)
{
for (PFObject *hospital in hospitals)
{
if ([hospital.objectId isEqualToString:#"NMZ8gLj3RE"])
{
[hospital deleteInBackgroundWithBlock:^(BOOL succeeded, NSError *error) {
if (succeeded){
NSLog(#"BOOOOOM"); // this is my function to refresh the data
} else {
NSLog(#"DELETE ERRIR");
}
}];
}
}
}
else
{
NSLog(#"%#",error);
}
}];