Transformable images stored in CoreData - will it work with pre-seeded database?

Question

If I use the "Transformable" attribute in Core Data to store images, it is my understanding that Core Data may or may not store it in the persistent store based on file size. Normally I wouldn't care where it stored the image, but for this app I need to ship it with a pre-seeded database in case an internet connection is not found when the app is first launched. So I basically want to take a snapshot (including images) of the database and have it load the first time the app is launched.

My question is, if Core Data decides for whatever reason to not use the persistent store, will the images still get loaded when I load the pre-seeded database? Or will it be broken because the image(s) were stored in some magic area that no longer exists when the user installs on their own device?

Answer 1

Making an attribute transformable has nothing to do with using external storage. The Store in External Record File option is available for both binary attributes and transformables, but is not required for either.

If you have an attribute that is transformable and uses external record files, you're correct that Core Data decides whether to actually use an external file based on its own undocumented logic (but probably by checking the size). Those external files get saved in a subdirectory of the one where the data store is located. If your data store is named Foo.sqlite, then in the same directory where that file is found is a directory named .Foo_SUPPORT/_EXTERNAL_DATA/. You can deal with this in a couple of ways:

• Copy the entire directory where Foo.sqlite lives, including dot files. This is preferred, because the path to the external references directory is undocumented and (in theory) could change. You'll get the external references but you don't need to hard-code the directory name.
• Copy the directory directly, since you know where it is. Probably a less good idea, for reasons described above.

Or if you prefer, just don't use external references. They're not required for any attribute, and if you like you can just have all of your data in a monolithic SQLite file.

Answer 2

You can just tell core data to use external storage for your images, and make it not having to figure it out when to use it and use it all the time. You can find the option to assign a property to use external storage on the core data inspector of your property.