Calculating columns with Core Data like SQL
cocoa, cocoa-touch, core-data, iphone, objective-c
Solution
CoreData itself can't really do this, because `distanceFromCurrentLocation` here would be a transient property (and you can't fetch on transient properties). But you can still do this in a natural way by fetching the objects into an NSMutableArray, and then sorting that array based on a `distanceFromCurrentLocation` transient property.
Depending on how often you do this and how often the user moves far enough to require recalculation, it could be more efficient to occasionally recalculate a `-currentDistance` persistent property, and then using simple predicates. This is a very efficient solution if you search much more often the user moves, because you can easily keep a single `locationOfLastRecalculation` persistent variable and only recalculate once when the user moves sufficiently. Since this would persist over restarts, the overall performance improvement over dynamic calculation could be substantial.
Problem
I am sorting stores to get the closest stores. Furthermore I want to know how far away this shop is. The SQL query would look like this: ``` select *, 6371 * 2 * ATAN2(SQRT(POWER(SIN((RADIANS(?) - RADIANS(latitude))/2),2) + COS(RADIANS(latitude)) * COS(RADIANS(?)) * POWER(SIN((RADIANS(?) - RADIANS(longitude))/2),2)), SQRT(1-POWER(SIN((RADIANS(?) - RADIANS(latitude))/2),2) + COS(RADIANS(latitude)) * COS(RADIANS(?)) * POWER(SIN((RADIANS(?) - RADIANS(longitude))/2),2))) AS DISTANCE FROM stores ORDER BY DISTANCE ``` these question marks would be replaced by the longitude and latitude of the users position. (latitude, latitude, longitude, latitude, latitude, longitude) How can I achieve this with iPhone SDK using Core Data?