具有核心数据的复杂分类标准

Question

I'm trying to sort my records stored in core data with some problems. In detail, I've two main issues:

1# Sort condition based on child records:

I have two entities (father and child) with a 1:M relationship, so one father can have more children. I would like to perform a sort of father records, based on the name of the older child. So basically, I should perform a search on the child records for a certain father and retrieve the name of the child with the maximum age, and do a sort of the fathers based on this information. How can I write the sortdescriptor?

2# Sort condition based on a calculation:

I have a list of addresses in my entity. For each line I've a column for the corresponding latitude and one for the longitude. Based on the current position, I would like to sort these records from the nearest to the farthest. Since the distance depends from the user position, it is a variable information and so it isn't stored in my core data table. So, how to sort these records? What is the best approach?

Every suggestion will be really appreciated!

Thanks you in advance, yassa

Answer 1

Could you use some compare operation on the result set?

Compare method

- (NSComparisonResult)compare:(Person *)otherObject {
    return [self.child compare:otherObject.child];
   }

NSArray *sortedArry;
sortedArry = [parentArray sortedArrayUsingSelector:@selector(compare:)];

BLOCKS

NSArray *sortedArry;
sortedArry = [parentArray sortedArrayUsingComparator:^(id a, id b) {
   NSString *first  = (Child*)a.name;
   NSDate   *second = (Child*)b.name;
   return [first compare:second];
}];

NSSortDescriptor

NSSortDescriptor *sortDescriptor;
sortDescriptor = [[[NSSortDescriptor alloc] initWithKey:@"child.name"
                                          ascending:YES] autorelease];
NSArray *sortDescriptors = [NSArray arrayWithObject:sortDescriptor];
NSArray *sortedArry;
sortedArry = [parentArray sortedArrayUsingDescriptors:sortDescriptors];

I am interested in seeing what your answer is. I have had a similar issue.