I have a quiz app which uses Parse.com for some data storage, app has a local sqlite database to store quiz related data. Now I want to store all the quiz database on Parse and download and store it into sqlite when the app runs first time. How is it possible and what is the best way to do that.
I think in your case it may be possible to rely largely on the Parse cache. As Alexandre pointed out in his answer, accessing the cache is a matter of setting the cachePolicy of your PFQuery correctly. However, keep in mind that you don't have control over this cache. According to the Parse docs:
Parse takes care of automatically flushing the cache when it takes up
too much space.
You will have to do some testing with your actual data and see if you run into the limitations of the Parse cache. You may also run into limitations with your pdf files. I imagine you would store these on Parse as PFFiles. PFFiles are caches on your local device, but again, you don't have full control over when those caches are deleted and you probably have to test the limits of this system. You can always fall back to re-downloading missing data.
Why would you use sqlite instead of cache/
You can use for example:
PFQuery *query = [PFQuery queryWithClassName:#"TestObject"];
query.cachePolicy = kPFCachePolicyCacheElseNetwork;
Related
We are wanting to implement an offline mode for our react-native application. We will be working with quite large amount of data (aprox. 40-50mb). It is an array of aprox. 16000 objects.
As far as I know, there are two ways to save this data.
Using AsyncStorage - android has a limit of 6mb, but I've read somewhere, that it can be increased.
Using json file - Downloading that data as json file using react-native-background-downloader and then using react-native-fs to save it and load it if the user has no connection to internet.
Personally I think that the second option is better, even though it requires permission to file storage.
Am I missing any other factors to consider? Are there any other options for offline access?
In the end opted out for usage of the json file as there is limit on android. On load of the application I take these data and load them into variable in mobX store. Which functions same as any variable.
I was afraid that mobile phones will have problem sorting across the 16000 objects in array, but there have been no reports of this thing going wrong so far. (In production for 4-5 months right now)
So basically when you hit "enable offline mode" I ask for the file storage permission and download the file using react-native-fs.
Then on the next startup of the application I just read the data off the JSON file.
For our app we need the app the work offline 100% with the most recent data.
Normally the app uses a symfony api platform API to fetch data paginated server side.
But when someone is using the app in a area without Internet he still need to be able to access all data to make a new job and que it for when he is online.
So our tough is to make a json that has all the data and send it to the phone when the phone has connection.
When the phone is using the app live, it will use pagination from server and fetch data.
And when offline it will use the local downloaded data file.
Problem is the data is large, so storing it is the problem.
We are now using redux persist and we see so many people have problems with crashes and mobile ram.
We also thought of using sqlite or just async to store a json file, or download a sqlite file from the app.
How do you guys feel about this
You can use react-native-local-mongodb. This can help you store a json database on your phone.
Other option is to have react-native-sqlite-storage in case your database has to be relational and requires table.
You will have to sync this local copy with the server once this user is online. This too can be done if you have the timestamp saved of the last sync. So after that, you ll just have to sync the data created after that timestamp.
However, I had also implemented react redux persist and it didnt crash. I suppose, the reason for crash must me something else.
I'm planning to launch a simple Node.JS utility and push it to heroku. A fire and forget solution, will sleep for like 90% of the time probably. Unfortunately it seems that I require a persistent data storage for my purposes (heroku apps get rebooted daily and storing everything in RAM is unrealistic), and I don't know which way to look as:
Most SQL hostings are paid / limited time free / require constant refreshing ( like freemysqlhosting ).
Storing stuff in plain .txt format is seemingly hard to implement, besides git always overwrites the contents of a tracked .txt file, and leaving it untracked disposes of it on heroku and leads to ENOENT No such file error. Yeah, I tried.
So, the question is - how do I implement a simple and built in solution for storing data? Are there any relevant typical solutions? It's going to be equivalent to just 1 SQL table.
As you can see, you can answer this on many levels - maybe suggest a free deploy and forget SQL hosting (it obviously has to support external connections), maybe tell me how to keep a file tracked in git without actually replacing all of its content with every commit, maybe suggest some module to install. I hope this is not too broad..
Over many different Objective-C iOS coding projects I have frequently come across the issue of having data be accessible after I initially got it.
For example, currently I am reading from the stackoverflow API. I do this with a session and get a dictionary back (my JSON response).
But outside the scope of the session, the dictionary is unavailable! I can't copy the contents to a different dictionary that I've defined globally, or anything. It's like it disappears outside of the session.
So I am wondering, what's the best way to save this data that I want to use? From what I've been reading it seems like NSUserDefaults or maybe creating a plist file, although admittedly I've been having trouble with both options. If there is a method that is best for this then I can concentrate on that.
Thank you!
It depends on how persistent you want to be.
If you save this dictionary into a global variable, it is stored in the part of device's RAM that is reserved for the running app. When the app stops running (gets killed by OS or removed by the user) or if your device reboots - this memory is lost.
If you save this dictionary onto the device's flash memory drive (and its file system) - it will live past restarts/reboots.
Usually people combine the approaches: when you get the data from the network, you keep it in a global variable, and save it to the file system. After the app restart you try to load the data from the file system. The reason for not using the FS all the time is that it is much slower than RAM access. I guess I'm describing caching.
Note that you can implement manual caching (using plain data or text files, NSUserDefaults, Core Data or other libraries), but also you can utilize a builtin HTTP cache - NSURLCache. If you create a session with NSURLSession.sharedSession it will use the default NSURLCache and respect a caching policy dictated by the server side.
For more control and full offline support I'd recommend to implement caching manually. See this about reading and writing plists and writeToFile:atomically:.
I have an iOS 7 app, that is using Core Data. Some of the Core Data objects has a related (one to one relationship) images that are > 1MB & < 4MB and are stored in the app’s Document folder. Core Data objects only stores image names as string.
I want to integrate iCloud support for the app so I can sync data between devices. I am planning to use iCloud Core Data storage to sync Core Data objects. But what to do with the images?! After reading different posts, I found a couple of options that are highlighted underneath. I am struggling to pick one, that would suit me best. It would be nice to know someones experience/recommendations. What I should be careful with, or what didn't I think of? I also need to consider migration of the existing data to the option I will pick.
OPTION 1. Store UIImage in the Core Data as Binary Data with External Binary Data option (read here). At this moment is seems to be the easiest solution, but I guess not the best. From Documentation:
It is better, however, if you are able to store BLOBs as resources on
the filesystem, and to maintain links (such as URLs or paths) to those
resources.
Also will the external files be synced? If so, how reliable the sync would be if the user quits on minimises the app, will the sync process resume? From objc.io about External File References:
In our testing, when this occurs, iCloud does not always know how to
resolve the relationship and can throw exceptions. If you plan to use
iCloud syncing, consider unchecking this box in your iCloud entities
OPTION 2. Store images using UIDocument (good tutorial here) and somehow track relation between Core Data entry and UIDocument. From what I understand whatever I put in this directory will be automatically synchronised to the iCloud by a system daemon. So if the user quits the app, the images will still be synced to the iCloud, right?
OPTION 3. Using FileManager(more info here). I haven’t read a lot about this approach, but I think it can also work.
OPTION 4. Any other?
There are similar posts (e.g. Core Data with iCloud design), but unfortunately they don't fully answer my question.
Seems Apple will reject application because of large database iCloud synchronization.
I think the best solution is to store images on a remote host, and keep Image URL in CoreData.
And also Local path of image should be resolvable from remote URL.
So the algorithm will look like this ->
1) Getting Remote URL from CoreData.
2) Resolve local path of image.
3) If local image exists retrieve it, otherwise read it from remote and save it to local storage.
You can have a look to Amazon S3 server here.