ios - Merging main and private contexts with Core Data -

i'm creating temportary contexts in private queue asynchronously update data persist core data:

nsmanagedobjectcontext *privatecontext = [[nsmanagedobjectcontext alloc] initwithconcurrencytype:nsprivatequeueconcurrencytype]; appdelegate *appdelegate = [[uiapplication sharedapplication] delegate]; privatecontext.persistentstorecoordinator = appdelegate.persistentstorecoordinator;  [privatecontext performblock: ^{      // parse files and/or call services , parse     // responses      dispatch_async(dispatch_get_main_queue(), ^{         // notify update user     }); }]; 

then, once i've got new data, need merge changes main context. know common scenario, i'm not sure how should proceed... apple's core data documentation section talks setting merge policy , don't understand way handle that. on other hand, found link, scenario described in "stack #2" section , says looks simpler, , doesn't talk merge policies @ all...

which correct or appropriate way should be? i'd appreciate explanation and/or simple example of how manage scenario.

thanks in advance.

what have there looks pretty good.

you using private queue work, , it's being saved persistent store.

if have small number of changes, fine. in case, want handle nsmanagedobjectcontextdidsavenotification context, , merge changes other context with

[context mergechangesfromcontextdidsavenotification:notification]; 

however, if doing lot of changes, want separate persistent store coordinator (attached same store). doing this, can write store, while mocs on other psc reading. if share psc other readers, 1 access @ time , cause readers block until write has finished.

also, if doing lots of changes, make sure them in small batches, inside autoreleasepool, saving after each batch. take @ similar question: where should nsmanagedobjectcontext created?

finally, if doing lots of changes, may more efficient refetch data process merges. in case, don't need observe notification, , don't need merge. it's pretty easy. note, if this, should have separate psc... if want save , notify in small-ish batches.

[privatecontext performblock: ^{      // parse files and/or call services , parse     // responses      dispatch_async(dispatch_get_main_queue(), ^{         // refetch data want... if on ios, simple         // telling fetched results controller refetch, ,         // reloading table view (or whatever else using data).     }); }];