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POHow does context saving work in Core Data
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copied!<p>I have a data base in my app. I use core data. I need to refresh my local data base with information coming from the server. I want to reduce time of updating DB. Let's say i have a table with 3 fields "ID", "Name", "file". In the "file" attribute is saved some large binary data. Here is the code to update my DB.</p> <pre><code>NSEntityDescription *entity=[NSEntityDescription entityForName:@"Entity" inManagedObjectContext:context]; NSFetchRequest *fetch=[[NSFetchRequest alloc] init]; [fetch setEntity:entity]; NSPredicate *predicate=[NSPredicate predicateWithFormat:@"ID == %@", newObject.objectID]; [fetch setPredicate:predicate]; NSError *fetchError; NSArray *fetchedEntities = [managedObjectContext executeFetchRequest:fetch error:&fetchError]; NSManagedObject *objectToUpdate = [fetchedEntities firstObject]; objectToupdate.name = newObject.name; BOOL isRecordUpdated = objectToupdate.isUpdated; // returns YES. NSError *saveError; [managedObjectContext save:&saveError]; </code></pre> <p>I found a record with ID and changed its name then saved the context. Object is changed and I can be sure it is updated on the server. The question is how does the update work. Will it rewrite the whole record? I mean what happens with the "file" attribute is it also rewritten? If yes, then how to avoid rewriting of large fields that are not changed. </p> <p>One more case. What if I rewrite the name with a new equal String?</p> <pre><code>NSString *name = [NSString stringWithFormat:@"%@", objectToUpdate.name]; BOOL nameChanged = firstName != contact.firstName; // returns YES BOOL nameIsEqual = [firstName isEqualToString:contact.firstName]; //returns YES objectToUpdate.name = name; BOOL hasChanges = [NSManagedObjectContext.defaultContext hasChanges]; //returns YES </code></pre> <p>I didn't change the name content but i changed the name value. If i save the context will it rewrite the Data Base? The aim of this question is to understand how to efficiently work with core data. Should i write custom properties to compare contents of strings, or should i store large data in a distinct table? Thanks for reading so far and sorry for being verbose.</p>

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