Provide example for why it is not advisable to store images in CoreData?

Question

this question has been asked many times, I have read many users telling that it is not advisable to store images in a DB, in particular within CoreData. By they all seems to

Answer 1

Leonardo,

With Lion/iOS 5, Core Data started handling file system storage of large BLOBs for you.

The choice is really determined by how many images you are going to have open. If you have many, then you should keep them in the DB. Why? Because you only have a modest number of file descriptors, one of which is used for each open image stored in the file system.

That said, there is still a reason to manage the files yourself. If your BLOBs are really big, say 2+ MB, you will want to map them into memory and not just read them in. (When the memory warnings come, this lets the OS automatically purge them from your resident memory. This is a very good thing.) Even so, you still have the limited number of file descriptors problem.

Andrew

Answer 2

There's nothing special about what Core Data normally does here. It's just using an SQLite database. You can put large blobs of data into it, but it just doesn't scale all that well. You can read more about it here: Internal Versus External BLOBs in SQLite.

That said, Core Data has support for external blobs which in Core Data terminology is called stored in external record (iOS 5.0 and later). Again, there's nothing magic about it, it's just storing the large pieces of data in the file system separately from the SQLite db itself. The benefit is that Core Data updates all this for you.

When you're in Xcode, there'll be a checkbox called Allows External Storage that you can check for Binary Data properties.

Answer 3

The filesystem, and the API:s surrounding it is (just like a webserver) optimized to serve files, of any size, and to apply caching where appropriate.

CoreData is optimized for handling an object graph with tiny pieces of data, like integers and short strings.

Also, there are a number of other issues that tend to creep up on you, like periodically vacuuming the SQLite database CoreData uses, or it won't be able to shrink, just grow.