问题
I have saved data into db using CoreData. I need to fetch data from my table in same order that it was saved. Inside table it is ordered by Z_PK - hidded CoreData key. How can I create such sort descriptor. If I use fetch request without sort descriptors my data objects have wrong order.
回答1:
Anything not exposed to you by the Core Data framework is an implementation detail. The fact that Z_PK exists, and currently suits your purposes, cannot be relied upon.
If creation/save order is important to your model, then it should be included in your model. There's really nothing else to it.
回答2:
There is no proper method in core data framework to sort object by primary key, but I think we can use objectID as a the primary key and sort by objectID. ObjectID for a particular object would always increase.. thus you can use below method
/*!
@param <NSManagedObject> array
@return <NSManagedObject> sortedarray
*/
+ (NSArray *) sortManagedObjectArrayByObjectID:(NSArray *) array {
NSArray *compareResult = [array sortedArrayUsingComparator:^NSComparisonResult(NSManagedObject *obj1, NSManagedObject *obj2) {
NSString *s = [obj1.objectID.URIRepresentation lastPathComponent];
NSString *r = [obj2.objectID.URIRepresentation lastPathComponent];
return [s compare:r];
}];
return compareResult;
}
Hope this would help
回答3:
Use a sort descriptor with self as the sort key. The underlying SQL will have ORDER BY t0.Z_PK.
来源：https://stackoverflow.com/questions/12949540/ios-get-objects-from-coredata-sorted-by-primary-key