Iphone Development

NSExpression The relatively new NSExpression class is incredibly powerful, yet not really gived actually lots. Part of that is that its not very hale documented. Although the API documentation for NSExpression is fairly well detailed, the listed companion withdraw (Introduction to Predicates Programming) has very little information about how to actually use NSExpression. NSExpression deserves to be better documented, because it brings to predicate programming (including Core Data), a share of f feed inures from the relational database world that people often remonstrate are missing, like unioning, intersecting, and subtracting resultsets and performing aggregate trading operations without load managed aspirations or faults into memory. The aggregates functionality is especially important on iOS given up the special(a) memory on most iOS devices. If youve got a large dataset, and you liking to get a count of objective lenss, or calculate an median(a) or means for one of the attributes, you really dont desire to ease up to pull the entire dataset into memory. Even if theyre just faults, theyre going to course up memory you dont need to use because the underlying SQLite large store can figure that stuff out without the object overhead.

I dont have time to do a dear NSExpression tutorial, but I thought it at least harm posting a category on NSManagedObject that lets you take sustenance of some of its more useful features. With this category, to get a core of the attribute  forfend on entity Foo, you would do this: NSNumber *fooSum = [Foo aggre gateOperation:@sum: onAttribute:@bar withPre! dicate: nonentity inManagedObjectContext:context]; This will calculate it for you using the database features, NOT by load all the managed objects into memory. Much more memory and mainframe computing device efficient than doing it manually. Cheers. Category follows: Header File: @interface NSManagedObject(MCAggregate) +(NSNumber *)aggregateOperation:(NSString *)function...If you loss to get a full essay, order it on our website: BestEssayCheap.com

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