Grabbing first image for each object in Parse iOS - ios

Question

Sorry for the poorly worded title. I have a logic issue that I'm trying to get my head around. The view that I'm working in has a UICollectionView that displays a list of "tanks" associated with a user. This collection view displays a three items:
Tank Name
Tank Capacity
Last Image Stored
The last image stored part is where I'm having trouble. I'm making progress but its a matter of the logic behind it that I'm not sure on. Here is what the data looks like:
I have two classes that I'm interacting with; SavedTanks and SavedTankImages. The unique objectId from a saved tank is also stored as a value in SavedTankImages to allow a sort of pointer reference to the image. This logic works when the user loads a "tank" and can see all of the images they've stored associated with it.
However, for the purposes of this view, I only need to grab the first image from each tank and display that. This is where I need help. Here's what I have so far:
#pragma mark COLLECTION VIEW
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *CellIdentifier = #"Cell";
photoHandler *cell = (photoHandler *)[collectionView dequeueReusableCellWithReuseIdentifier:CellIdentifier forIndexPath:indexPath];
_tankNameArray = [_array objectAtIndex:indexPath.section * 1 + indexPath.row];
cell.tankNameLabel.text = [_tankNameArray valueForKey:#"tankName"];
cell.tankCapLabel.text = [_tankNameArray valueForKey:#"tankCapacity"];
NSArray *objectId = [_array valueForKey:#"objectId"];
for (int i = 0; i < objectId.count; i++)
{
NSString *objectString = [[NSString alloc] init];
objectString = [objectId objectAtIndex:i];
PFQuery *imageQuery = [PFQuery queryWithClassName:#"SavedTankImages"];
[imageQuery whereKey:#"tankObjectId" equalTo:objectString];
[imageQuery findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) {
if (!error)
{
for (PFObject *object in objects)
{
NSLog(#"OBJECT TEST: %#", object);
}
}
}];
}
return cell;
}
On OBJECT TEST: %#, this is the logged output:
2014-05-28 11:59:44.750 ReefTrack[305:60b] OBJECT TEST: <SavedTankImages:U6fRTuRo2c: (null)> {
tankImages = "<PFFile: 0x18a25890>";
tankObjectId = tsz4yvrIAN;
}
SavedTankImages: <x> is the objectId of the individual image, and tankObjectId is the tank the image is associated with. I'm getting close, but I need to know how I can effectively iterate and only grab the first item where tankObjectId matches the original objectId. Please forgive me if this sounds a little convoluted.
Thanks for the help in advance as usual.
UPDATE
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *CellIdentifier = #"Cell";
photoHandler *cell = (photoHandler *)[collectionView dequeueReusableCellWithReuseIdentifier:CellIdentifier forIndexPath:indexPath];
_tankNameArray = [_array objectAtIndex:indexPath.section * 1 + indexPath.row];
cell.tankNameLabel.text = [_tankNameArray valueForKey:#"tankName"];
cell.tankCapLabel.text = [_tankNameArray valueForKey:#"tankCapacity"];
NSArray *objectId = [_array valueForKey:#"objectId"];
for (int i = 0; i < objectId.count; i++)
{
// NSString *objectString = [[NSString alloc] init];
// objectString = [objectId objectAtIndex:i];
PFQuery *imageQuery = [PFQuery queryWithClassName:#"SavedTankImages"];
[imageQuery whereKey:#"tankObjectId" equalTo:[objectId objectAtIndex:i]];
[imageQuery getFirstObjectInBackgroundWithBlock:^(PFObject *objects, NSError *error)
{
if (!error)
{
PFFile *imageFile = [objects valueForKey:#"tankImages"];
[imageFile getDataInBackgroundWithBlock:^(NSData *data, NSError *error) {
if (!error)
{
cell.parseImage.image = [UIImage imageWithData:data];
}
}];
NSLog(#"Heres your image: %#", objects);
}
}];
}
return cell;
}
The above code selects the first available image and makes it the background for every cell in collectionView. I want to get it so that it only returns the first image for the objectId. In other words
Tank 1 = tank 1 image 1
Tank 2 = tank 2 image 1
Tank 3 = tank 3 image 1
Right now this is what it's doing:
Tank 1 = tank 1 image 1
Tank 2 = tank 1 image 1
Tank 3 = tank 1 image 1

Answer 1

Simple solution, sort and take just the first result. Be aware this isn't as efficient as the next solution:
// sort by createdAt or use updatedAt
[imageQuery orderByDescending:#"createdAt"];
// change from find to getFirst
//[imageQuery findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) {
[imageQuery getFirstObjectInBackgroundWithBlock:^(PFObject *object, NSError *error) {
if (!error)
{
NSLog(#"OBJECT TEST: %#", object);
}
}];
A more advanced solution if you'll often be querying on this is to store a pointer to the most recent object on the tank. You can either do this in your code or create a Cloud Code method to update it automatically after each SavedTankImages object is saved (it would simply load up the related SavedTanks and set mostRecentImage to point to the saved image, then save the SavedTanks).
If you have done this, then you can just use the include: method to load the mostRecentImage with the SavedTanks.