Using Delta in Dropbox API with iOS - objective-c

Question

I'm using the dropbox api for iOS and have been messing with the loadDelta function. I get the whole "key" that is sent, and I get how the structure is set up (see below this code), but what I don't understand is how to download the file that is sent and how to save it to the iOS device. Does anyone have any insight on how to do this?
-(void)restClient:(DBRestClient *)client loadedDeltaEntries:(NSArray *)entries reset:(BOOL)shouldReset cursor:(NSString *)cursor hasMore:(BOOL)hasMore{
for (DBDeltaEntry *file in entries) {
if(!file.metadata.isDirectory){
NSLog(#"File: %# ", file.metadata.filename );
}else {
NSLog(#"Directory: %# ", file.metadata.filename );
}
}
}
The call sends back an array called entries. Each entry in entries is this:
#interface DBDeltaEntry : NSObject {
NSString *lowercasePath;
DBMetadata *metadata;
}
with the DBMetadata object being:
#interface DBMetadata : NSObject <NSCoding> {
BOOL thumbnailExists;
long long totalBytes;
NSDate* lastModifiedDate;
NSDate *clientMtime; // file's mtime for display purposes only
NSString* path;
BOOL isDirectory;
NSArray* contents;
NSString* hash;
NSString* humanReadableSize;
NSString* root;
NSString* icon;
NSString* rev;
long long revision; // Deprecated; will be removed in version 2. Use rev whenever possible
BOOL isDeleted;
NSString *filename;
}
What I can't figure out is how to recursively set up my offline structure or the best practice for doing so. My assumption is though, using delta, I won't need to keep a database of the files I have saved for update purposes, right?

Answer 1

The /delta call only tells you what has changed. It doesn't itself give you any access to the file contents. If you want to download any particular file that you heard about from /delta, you should use the path it gave you with the /files (GET) call to download the file:
https://www.dropbox.com/developers/reference/api#files-GET
(The iOS SDK makes this available as the loadFile function.)
The /delta call does save you the trouble of having to call /metadata to manually figure out what has changed and keep track of the current state, but note that the Dropbox API best practices ( https://www.dropbox.com/developers/reference/bestpractice ) do say that you shouldn't download anything until the user asks for it.

Answer 2

One scheme is to use a SQLite table with the following columns:
lc_path: The lowercase'd path of the file (primary key for this table)
name: The name of the file
lc_parent_path: The lowercase'd path of the parent folder
other metadata... (last modified, revision, is_dir, etc.)
So when processing an "add" /delta entry, you insert a row into the table (you might have to replace an existing row).
When processing a "delete" entry for the path /a/b/c, you need to delete all children as well, so you can do DELETE ... WHERE lc_path = "/a/b/c" and then DELETE ... WHERE lc_path LIKE "/a/b/c/%".
If you want to query the database for a list of immediate children of the folder "/a/b/c", do SELECT ... WHERE lc_parent_path = "/a/b/c"
You may have noticed that you the path is stored somewhat redundantly (lc_parent_path+name and lc_path). This probably won't be a problem. But if you find that your database is too large and that most of the space is going toward storing the path strings, there are encoding tricks you can do.