CODEWITHSUNDEEP
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Katedral Pillon
Katedral Pillon

Reputation: 14864

Should I save my images in Core Data or should I use SDWebImage

I have been developing an app with cloud/server data source. So naturally the process is one thing at a time. So at present, to fill my tables, I query the server which returns an array. The array contains urls to images and then from the urls I load the images using SDWebImage.

Now I am entering the stage of development where I need to implement Core Data for all the data in my tables (i.e. texts and images). So far I am considering the following approaches:

Of course the point here is that if I use SDWebImage it will save the image in its own caching system, which from my limited understanding may or may not be entirely consistent with what is in core data. On the other hand I don't understand core data enough to know if it handles saving images well in terms of performance (i.e. knows it's an image and therefore handle the file linking).

So What is the best way to do this? Can SDWebImage work in harmony with Core Data? Or is SDWebImage redundant since core data is good enough all by itself?

Another thing to note is that presently, my data loads from server immediately and then the images come as SDWebImage loads each into its UIImageView. This may not be a problem with Core Data since ideally the image will be in the local DB. Any thoughts?

Upvotes: 1

Views: 1406

Answers (2)

quellish
quellish

Reputation: 21244

Based on your question and comments, it seems you are trying to locally cache images that were retrieved through an HTTP request.

The URL loading system is already caching the images. There is no need to implement another layer of caching on top of that, wether it be SDWebImage or CoreData. When an HTTP response is received from the server, the server includes "freshness" information that informs the client how long and under what conditions that response is valid. The URL loading system, by default, obeys those rules. You can check the freshness information of responses using a tool like Charles or REDBot. The server is the only party in this conversation that can know how long a response is valid for.

The URL loading system does not, by default, cache to the filesytem - only in-memory. This is easy to change:

cache = [[NSURLCache alloc] initWithMemoryCapacity:(1024*1024*512) diskCapacity:(1024*1024*1024 * 100) diskPath:@"Cache.db"];
[NSURLCache setSharedURLCache:cache];

Or when using NSURLSession:

cache = [[NSURLCache alloc] initWithMemoryCapacity:(1024*1024*512) diskCapacity:(1024*1024*1024 * 100) diskPath:@"Cache.db"];
[sessionConfiguration setURLCache:cache];
session = [NSURLSession sessionWithConfiguration:sessionConfiguration];

Storing image data in Core Data is something in general to be avoided, at least with the NSSQLiteStoreType persistent store. Even small images are large in the SQLite database and cause fragmentation, etc. that impact performance. If you are going to store image data in Core Data, it's preferable to use external storage - either by use Core Data's own external records storage, or by storing image data on the filesystem and referencing it in managed objects by using URLs.

However, if you are using Core Data OR SDWebImage to "cache" images, you are ignoring the freshness information that was returned in the server's response unless you implement your own validation layer - which the URL loading system is already doing for you!

Upvotes: 3

Mundi
Mundi

Reputation: 80265

Regardless of the question semantics, I think you need some more hard information to inform your decision.

It would be useful for you to know that storing large images (larger than, say, thumbnails) is not recommended and will lead to performance issues. Core Data has an option for large data where you can check "Store in External Record File". Alternatively, you can administer your own cache data (in this way you can flexibly update the images via download on a per-need basis on each device sharing the same data). The accepted best practice is to only store the image URL in Core Data (typically relative to the application directory) and handle the file storage / display separately.

I do not know SDWebImage, but this might provide some of the functionality that you need in the light of the above.

I hope this helps you make your decision about the data architecture.

Upvotes: 2

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