I've started prototyping some enhancements to support "subsetting" — syncing a
subset of the server database to the device, but being able to pull more
documents to the device as needed. These are on a branch of the iOS repo called
feature/subset
<https://github.com/couchbase/couchbase-lite-ios/commits/feature/subset>.
Please feel free to check it out and follow along :)
So far there are two new features:
1. A new replication property called "add_docs". It's a boolean that defaults
to true, but setting it to false tells a pull replication to not create any
docs locally — that is, it won't pull a doc from the server if there isn't
already a doc with that ID in the local database. This feature will keep a
subsetted database up to date, by pulling new revisions of the docs in the
local subset without bringing in all of the available remote docs.
You enable it like this:
repl.customProperties = @{@"add_docs": @NO};
2. A new CBLReplication method -pullDocumentIDs:. It takes an array of strings
and pulls the documents with those IDs from the server. (For obvious reasons
this only works on a pull replication.) This method ignores filters and the
add_docs property. There's not yet any progress information or error
notification other than what's already available on the CBLReplication.
You can combine these features by creating an add_docs=NO pull replication at
launch, and then calling -pullDocumentIDs: on it to load documents as you need
them.
What's still missing:
Making purge prevent the document from coming back when it's updated on the
server. (An add_docs=NO replication won't re-add it, but a regular pull
replication will.)
Progress info for individual document pulls
Being able to query the remote database to find documents to pull
More…?
—Jens
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