How to sort the relational data?

Question

Only a little question:

I have an Entity X with an to-many relation to Entity Y

In the viewDidLoad method i fetch all X and sort them by name and ascending and they are displayed in a tableView.

If you choose one of the Xs in the tableView, all relational Y´s are shown in a second tableView. The result of this fetch also includes all relational Y´s for every X, so i dont have to do an extra fetch for the Y´s - but that leads to my Problem: The Y´s are in a completly random order (which also changes with every restart of the app) - but i want them sorted by date (<- a attribute in the Y Entity)... how can i do that?

Heres the fetch - code

NSFetchRequest *request = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:@"Customer" inManagedObjectContext:managedObjectContext];
[request setEntity:entity];

NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"firstName" ascending:YES];
NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil];
[request setSortDescriptors:sortDescriptors];

NSError *error = nil;
NSMutableArray *mutableFetchResults = [[managedObjectContext executeFetchRequest:request error:&error] mutableCopy];
if (mutableFetchResults == nil) {
    // Handle the error.
}

[self setCustomersArray:mutableFetchResults];

and the result looks something like this:

Entity X-1
 attribute-x-1
 attribute-x-2
 relation-attribute
  relation-entity-y-1
   attribute-y-1
   attribute-y-2
  relation-entity-y-1
   attribute-y-1
   attribute-y-2
Entity X-2
 attribute-x-1
 attribute-x-2
 relation-attribute
  relation-entity-y-1
   attribute-y-1
   attribute-y-2

maybe thats an better example:

Customer
 name: Bert
 age: 10
 customerMeasureRealtions
  Measure
   score: 5
   date: 10.10.2010
  Measure
   score: 9
   date: 20.20.2000
Customer
 name: Steve
 age: 20
 customerMeasureRealtions
  Measure
   score: 7
   date: 07.07.2007

after the fetch the "Customers" are sorted by "name". But if i access the "Measures" through a "Customer" the order of the "Measures" is random, but i want them sorted by "date".

the code for accessing the Measures ("customer" is a Customer-Entity-Object or Model), ("measuresForCustomer" is the customerMeasureRealtions):

- (void)loadMeasureDataForCustomer:(Customer *)customer
{
NSSet *customerSet = customer.measuresForCustomer;
measuresArray = [NSMutableArray arrayWithArray:[customerSet allObjects]];
[measuresTable reloadData];
}

more code please. And what is "dpo"? – Nick Weaver Mar 19 '12 at 16:43 — Nick Weaver, Mar 19 '12 at 16:43
dpo = do ;) i added some information/code – jacksbox Mar 19 '12 at 16:51 — jacksbox, Mar 19 '12 at 16:51
Ok, can you show us some code how you access the Measures? – Nick Weaver Mar 19 '12 at 16:57 — Nick Weaver, Mar 19 '12 at 16:57
sure, i added it at the end of the question – jacksbox Mar 19 '12 at 17:04 — jacksbox, Mar 19 '12 at 17:04

score 0 · Accepted Answer · edited May 23 '17 at 12:20

0

I think there are two ways you could do this:

Initiate a second query to your db and fetch the "measures" for a given Customer. Have a look at Core data, sorting one-to-many child objects for this.
Transfer the NSSet into an NSArray and sort it in place. An NSSet is always unordered. Have a look at How to sort a NSArray alphabetically?. Or Apple's documentation: sortedArrayUsingDescriptors in conjunction with a NSSortDescriptor.

edited May 23 '17 at 12:20

Community

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1

answered Mar 19 '12 at 17:16

Nick Weaver

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great! i used the first approach because i think the sorting by date is easier with core data. thanks a lot XD – jacksbox Mar 19 '12 at 17:38

score 0 · Answer 2 · answered Mar 19 '12 at 17:18

Use one of the sort methods of NSSet.

Try:

- (NSArray *)sortedArrayUsingDescriptors:(NSArray *)sortDescriptors

Or, if you get your NSArray from your NSSet, you then have a whole host of sorting methods on NSArray to pick from:

Sorting
– sortedArrayHint
– sortedArrayUsingFunction:context:
– sortedArrayUsingFunction:context:hint:
– sortedArrayUsingDescriptors:
– sortedArrayUsingSelector:
– sortedArrayUsingComparator:
– sortedArrayWithOptions:usingComparator:

These come from NSArray and NSSet API documents.

How to sort the relational data?

2 Answers2