My iOS Application has been in review, but was rejected regarding the iOS Data Storage Guidelines. In the end, it was rejected because my Core Data database (sqlite) was located in the /Documents folder. I'm was aware, that this folder should only be used, it the data could not be recreated by my application. The reason why I chose to put it there anyway was, that one of the entities in my database contains an attribute telling if the given news has been read. This information cannot be recreated. Is this not enough to put the database in the /Documents folder?
Another thing is, that the current version of my application does not use this value to visualize if the news item has been read or not. So, should I tell the review-team about this attribute and argument why I think it should be placed in the document-folder -- or should I just move it to the /Library/Cache/?
The app review team wants you to split your data apart. Store the re-creatable parts in the Cache folder and the stuff that can't be re-created in the Documents folder. It's okay if there's a little bit of stuff in Documents that could theoretically be re-created—nobody will even notice a title or datestamp—but long text documents, video, audio, or images should be kept in the Cache folder if they can be downloaded again later.
There are a couple different ways you could do this:
Store the downloaded content in the Cache folder and only put the content's filename in your Core Data database (or calculate the filename from something else, like the SHA-1 hash of the URL it was downloaded from). Make sure your code will re-download any content that's not in the cache.
Use two Core Data stores with a single store coordinator. Note that you can't split an entity's attributes across two stores, so you may have to break some of your entities in half. Nor can you create a relationship from an object in one store to an object in another, so you'll have to store the object ID URI instead. See "Cross-Store Relationships" in the "Relationships and Fetched Properties" section of the Core Data Programming Guide for more details.
Whatever you do, keep in mind that iOS may purge your Cache folder at any time. Be prepared for files in your Cache folder to have disappeared; if that happens, you should re-download the files as the user requests them.
Related
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.
I have a core data document based application. Part of my model works by having a DeviceType table, and a Devices table with a relation between them. I would like my application to be able to store the list of DeviceTypes separately from each file, and possibly be able to sync that to a server later.
What would be the best way to accomplish this?
Thanks,
Gabe
You're using a lot of database terminology with Core Data. You should break that habit as soon as possible (the reasons why are given in the introductory paragraphs to the Core Data Programming Guide).
I assume your "usually-static" device list is something you want to be able to update as new devices come out? I would actually recommend just storing the list as a PLIST resource in your app bundle and pushing an update to the app when new devices come out (for simplicity). Using a dictionary-based PLIST, your keys can be device IDs and that key can be a simple string attribute of your managed objects. It's perfectly reasonable to look things up outside your Core Data model based on some ID.
If you must update, I'd still include the "default" list with the app (see above) but if a ".devicelist" (or whatever) file is present in the documents folder, use that instead. That way you can periodically check for an updated list and download it to the docs folder if it differs.
If I've misunderstood you, I encourage you to clarify either by editing your question or posting comments.
I'm building an application that needs to download web content for offline viewing on an iPad. At present I'm loading some web content from the web for test purposes and displaying this with a UIWebView. Implementing that was simple enough. Now I need to make some modifications to support offline content. Eventually that offline content would be downloaded in user selectable bundles.
As I see it I have a number of options but I may have missed some:
Pack content in a ZIP (or other archive) file and unpack the content when it is downloaded to the iPad.
Put the content in a SQLite database. This seems to require some 3rd party libs like FMDB.
Use Core Data. From what I understand this supports a number of storage formats including SQLite.
Use the filesystem and download each required file individually. OK, not really a bundle but maybe this is the best option?
Considerations/Questions:
What are the storage limitations and performance limitations for each of these methods? And is there an overall storage limit per iPad app?
If I'm going to have the user navigate through the downloaded content, what option is easier to code up?
It would seem like spinning up a local web server would be one of the most efficient ways to handle the runtime aspects of displaying the content. Are there any open source examples of this which load from a bundle like options 1-3?
The other side of this is the content creation and it seems like zipping up the content (option 1) is the simplest from this angle. The other options would appear to require creation of tools to support the content creator.
If you have the control over the content, I'd recommend a mix of both the first and the third option. If the content is created by you (like levels, etc) then simply store it on the server, download a zip and store it locally. Use CoreData to store an Index about the things you've downloaded, like the path of the folder it's stored in and it's name/origin/etc, but not the raw data. Databases are not thought to hold massive amounts of raw content, rather to hold structured data. And even if they can -- I'd not do so.
For your considerations:
Disk space is the only limit I know on the iPad. However, databases tend to get slower if they grow too large. If you barely scan though the data, use the file system directly -- may prove faster and cheaper.
The index in CoreData could store all relevant data. You will have very easy and very quick access. Opening a content will load it from the file system, which is quick, cheap and doesn't strain the index.
Why would you do so? Redirect your WebView to a file:// URL will have the same effect, won't it?
Should be answered by now.
If you don't have control then use the same as above but download each file separately, as suggested in option four. after unzipping both cases are basically the same.
Please get back if you have questions.
You could create a xml file for each bundle, containing the path to each file in the bundle, place it in a folder common to each bundle. When downloading, download and parse the xml first and download each ressource one by one. This will spare you the overhead of zipping and unzipping the content. Create a folder for each bundle locally and recreate the folder structure of the bundle there. This way the content will work online and offline without changes.
With a little effort, you could even keep track of file versions by including version numbers in the xml file for each ressource, so if your content has been partially updated only the files with changed version numbers have to be downloaded again.
It would be useful for many people to know how to completely remove an application from your device when testing.
I have downloaded my app many times now, and likewise have deleted it many times. The problem is when deleting the app, it does not remove things like the persistent object related to my app, or the images downloaded through the app. So, when I download the next build, I have no idea if something broke that is related to building the persistent object or fetching the images since those elements already exist from the last build.
I don't know if this is a cache thing. I don't know if this is expected and I have to use some utility to wipe this data after deleting the app. I can't really find much info through basic web searches.
Any information would be appreciated.
Blackberry Bold 9000. 4.6 OS. tested with both SD card and no SD card.
Objects stored in the PersistentStore are automatically deleted on uninstall if their interfaces were defined in your project. If they are from the standard BlackBerry API then they will stick around until they're deleted. E.G if you save a String in the PersistentStore it will stay in the PersistentStore but if you save a class you created it will be deleted on an uninstall. So if you want to have those objects be deleted automatically just create a wrapper class and save that.
Images stored on the filesystem will not be deleted until you or some application deletes them. However, it should be easy for you to write an app that clears everything out.
Another solution you could implement is making your app somewhat self-aware of its data.
Create a simple String value that you persist (or optionally, persist it in a Hashtable so you can store many properties this way) that includes "Version".
At startup of the GUI app, compare the stored "Version" against the application's current version. If the stored version doesn't exist, or if it exists and matches, take no action.
If it exists and does not match, automatically clean up old persisted data; or alternatively prompt the user to see if they want that data to be deleted (which one is better will depend on your implementation)
You can also use CodeModuleListener to listen for an uninstall event -- when that happens, you can clean up at that time as well or instead.
(As an aside and a bit of shameless self promotion, I am actually currently working on a shareable library for Blackberry that makes managing persistence much easier, as well as desktop data backup/restore. I'm doing this as part of the BBSSH project, but I'll be splitting it off into a separate library of core components and publishing it under a dual GPL/optional commercial license. It will contain hooks for data cleanup and data versioning. )
For the past 5 years, my typical solution for storing uploaded files (images, videos, documents, etc) was to throw everything into an "upload" folder and give it a unique name.
I'm looking to refine my methods for storing uploaded content and I'm just wondering what other methods are used / preferred.
I've considered storing each item in their own folder (folder name is the Id in the db) so I can preserve the uploaded file name. I've also considered uploading all media to a locked folder, then using a file handler, which you pass the Id of the file you want to download in the querystring, it would then read the file and send the bytes to the user. This is handy for checking access, and restricting bandwidth for users.
I think the file handler method is a good way to handle files, as long as you know to how make good use of resources on your platform of choice. It is possible to do stupid things like read a 1GB file into memory if you don't know what you are doing.
In terms of storing the files on disk it is a question of how many, what are the access patterns, and what OS/platform you are using. For some people it can even be advantageous to store files in a database.
Creating a separate directory per upload seems like overkill unless you are doing some type of versioning. My personal preference is to rename files that are uploaded and store the original name. When a user downloads I attach the original name again.
Consider a virtual file system such as SolFS. Here's how it can solve your task:
If you have returning visitors, you can have a separate container for each visitors (and name it by visitor login, for example). One of the benefits of this approach is that you can encrypt the container using visitor's password.
If you have many probably one-time visitors, you can have one or several containers with files grouped by date of upload.
Virtual file system lets you keep original filenames either as actual filesnames, or as a metadata for the files being stored.
Next, you can compress the data being stored in the container.