Is there anything bad about reusing an NSFetchRequest for several different fetches with Core Data?
core-data, nsfetchrequest, nspredicate, xcode
Solution
It's not a problem, but in the example given it's not gaining you much (just some code brevity.) The most expensive part of creating a fetch request is parsing the predicate format string.
If the code you've given is called frequently, and you're looking to speed it up, here are some ideas to try:
- Create all the predicates and fetch request just once: maybe in a `dispatch_once()` block and storing them statically; or in the constructor and stored in object fields
- Don't specify sort descriptors, since order doesn't matter if you only care about the count
- If the actual predicates will be more complex or flexible than shown, create one general template predicate with substitution variables, and use `predicateWithSubstitutionVariables:` to generate specified copies.
- For even more code brevity, define that template in the object model using the model editor, and use `fetchRequestFromTemplateWithName:substitutionVariables:` to create fetch requests.
I can gin up some sample code if you like.
Problem
My question: Is there anything bad about reusing an `NSFetchRequest` for several different fetches with Core Data? Example code: ``` NSFetchRequest *request = [[NSFetchRequest alloc] init]; NSEntityDescription *logEntity = [NSEntityDescription entityForName:@"LogEntry" inManagedObjectContext:context]; [request setEntity:logEntity]; NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"dateTimeAction" ascending:NO]; // ascending NO = start with latest date [request setSortDescriptors:[NSArray arrayWithObject:sortDescriptor]]; NSPredicate *predicate = [NSPredicate predicateWithFormat:@"status == %@",@"op tijd"]; [request setPredicate:predicate]; [request setFetchLimit:50]; NSError *error = nil; NSInteger onTimeCount = [context countForFetchRequest:request error:&error]; NSPredicate *predicate1 = [NSPredicate predicateWithFormat:@"status == %@",@"uitgesteld"]; [request setPredicate:predicate1]; [request setFetchLimit:50]; NSInteger postponedCount = [context countForFetchRequest:request error:&error]; NSPredicate *predicate2 = [NSPredicate predicateWithFormat:@"status == %@",@"gemist"]; [request setPredicate:predicate2]; [request setFetchLimit:50]; NSInteger missedCount = [context countForFetchRequest:request error:&error]; ```