NSFetchRequest to show results in particular order

Question

Suppose I have one entity 'Person' in core data. Now i want to search all persons. Either firstname beginning match or lastname beginning match. For eg : 1) Amit Gupta 2) Ajay Gulati 3) Gunjan Aggarwal

Searching for 'Gu' shows names that match firstname first, then those that match lastname therefore result is :

Gunjan Aggarwal Ajay Gulati Amit Gupta

One option : Fetch all objects , store them in array and then sort. But what if the search results are very big in number

Second option : Use NSFetchedResultsController This will fetch all matching but not in the required manner(firstname before lastname). Cant use sort descriptors as it is not sorting on any key, but upon matching.

Can anybody help ?

EDIT : First name and lastname are two different attributes of 'Person' entity. Either Firstname matches or Lastname matches.

I want results with 'Firstname' match before than results with 'Lastname' match.

If you use sort descriptor, which 'Key' or 'attribute' will you mention ???

I don't understand clearly why you could not use NSSortDescriptor (which is intended for this use-case) ? — Vinzzz, May 14 '12 at 12:47
@YatinSarbalia no mater how many attributes, `NSSortDescriptor` works fine. ;) — Kjuly, May 14 '12 at 13:04
Lets take an example : 1) A B 2) A C 3) B D 4) B G 5) E B 6) E F I searched for 'B' Desired result is : (results that match first name comes first) 1) B D 2) B G 3) A B 4) E B Whereas if i use two sort descriptors as you said , the result would be : 1) A B 2) B D 3) B G 4) E B So incorrect solution i guess.... — Yatin Sarbalia, May 15 '12 at 04:46

Kjuly · Answer 1 · 2012-05-15T07:00:23.087

Try to set Sort Descriptors before fetching:

NSSortDescriptor * firstNameDescriptor;
firstNameDescriptor = [[NSSortDescriptor alloc] initWithKey:@"firstName"
                                                  ascending:YES
                                                   selector:@selector(localizedCaseInsensitiveCompare:)];
NSSortDescriptor * lastNameDescriptor;
lastNameDescriptor = [[NSSortDescriptor alloc] initWithKey:@"lastName"
                                                 ascending:YES
                                                  selector:@selector(localizedCaseInsensitiveCompare:)];
[firstNameDescriptor release];
[lastNameDescriptor release];

[fetchRequest setSortDescriptors:[NSArray arrayWithObjects:firstNameDescriptor, lastNameDescriptor, nil]];

then fetch your desired persons.

After you got a sorted result, in order to match your searching, you might need to resort it:

- (NSComparisonResult)compare:(id)anotherOne {
  // if the first name matches the searching key word, return NSOrderedAscending;
  // else return [self.firstName localizedCaseInsensitiveCompare:anotherOne.firstName];
}

then just apply this to your search result array with sortedArrayUsingSelector: method. No testing code available, but I think you can figure it out by yourself then. ;)

@YatinSarbalia I see..but you can find that `setSortDescriptors:` use an array, so just put both descriptors into the array. See the new version of answer. :) — Kjuly, May 14 '12 at 13:02
Lets take an example : 1) A B 2) A C 3) B D 4) B G 5) E B 6) E F I searched for 'B' Desired result is : (results that match first name comes first) 1) B D 2) B G 3) A B 4) E B Whereas if i use two sort descriptors as you said , the result would be : 1) A B 2) B D 3) B G 4) E B — Yatin Sarbalia, May 15 '12 at 04:45

trapper · Answer 2 · 2012-05-21T17:16:57.907

Use a transient property sortName in your Core Data object, make it compare the firstName and lastName properties and just return whichever comes first alphabetically.

Now just use this property as your sortDescriptor and you should get the result you are after.

Something like this...

- (NSString *)sortName
{
    [self willAccessValueForKey:@"sortName"];

    NSString *string = nil;

    if ([self.firstName compare:self.lastName] == NSOrderedAscending) {
        string = self.firstName;
    } else {
        string = self.lasttName;
    }

    [self didAccessValueForKey:@"sortName"];

    return string;
}

score 1 · Answer 3 · answered May 16 '12 at 23:25

1

Use two fetch requests. When you're providing data to the view, display the results of the first fetch request, followed by the results of the second.

answered May 16 '12 at 23:25

paulmelnikow

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NSFetchRequest to show results in particular order

3 Answers3