Core data filtering - ios

Question

I have a core data structure as follows:
Business <-------->> Employee <-------->> Address
Each business has multiple employees and each employee can have multiple addresses.
From the Business object, I want to be able to get an NSArray or NSSet of all the Address objects that specify a certain condition. E.g. All the street names have to be unique.
I know that I could override the isEqual: but I'm guessing this is going to have unintended results. Otherwise, I have been looking into using valueForKeyPath:#"#distinctUnionOfObjects", but I don't think I can pass a condition.
Here is some code that I have so far:
NSMutableArray *addressArray = [NSMutableArray array];
NSArray *employees = [Employee sortedArray];
//loop through employees
for (Employee *employee in employees) {
for (Address *address in employee.addresses) {
[addressArray addObject:address];
}
}
//filter out duplicates
addressArray = [addressArray valueForKeyPath:#"#distinctUnionOfObjects.city"];
This code gives me a list of unique cities, however, I want a collection containing Address objects that have unique city values (or some other condition).

Answer 1

I found a way to do this with the LinqToObjectiveC library:
NSArray* addressesWithUniqueCities = [input distinct:^id(id address) {
return [address city];
}];
Looking at the source, the underlying implementation is as follows:
typedef id (^Selector)(id item);
-(NSArray *)distinct:(Selector)keySelector
{
NSMutableSet* keyValues = [[NSMutableSet alloc] init];
NSMutableArray* distinctSet = [[NSMutableArray alloc] init];
for (id item in self) {
id keyForItem = keySelector(item);
if (![keyValues containsObject:keyForItem]) {
[distinctSet addObject:item];
[keyValues addObject:keyForItem];
}
}
return distinctSet;
}
My final code ended up being:
NSMutableArray *addressArray = [NSMutableArray array];
NSArray *employees = [Employee sortedEmployees];
//loop through employees
for (Employee *employee in employees) {
for (Address *address in employee.addresses) {
[addressArray addObject:address];
}
}
//filter out duplicates
NSArray *distinctAddressArray = [addressArray distinct:^id(id address) {
return [address addressLine];
}];
return distinctAddressArray;

Answer 2

I'm not sure this is what you meant but you could try something like: (untested)
+ (NSMutableArray*) addressesForBusiness:(Business*)business
sectionProperty:(NSString*)sectionProperty
{
NSFetchRequest* request = [[NSFetchRequest alloc] initWithEntityName:#"Address"];
request.predicate = [NSPredicate predicateWithFormat:#"employee.business == %#",business.objectID];
request.sortDescriptors = #[[NSSortDescriptor sortDescriptorWithKey:sectionProperty ascending:YES]];
NSArray* addresses = [business.managedObjectContext executeFetchRequest:request error:NULL];
NSMutableArray* sections = [NSMutableArray new];
NSMutableArray* currentSection = [NSMutableArray new];
NSManagedObject* prevAddress = nil;
for (NSManagedObject* address in addresses) {
if (prevAddress && ([[address valueForKey:sectionProperty] isEqual:[prevAddress valueForKey:sectionProperty]])) {
currentSection = [NSMutableArray new];
[sections addObject:currentSection];
}
prevAddress = address;
[currentSection addObject:address];
}
return sections;
}
This will return an array of arrays where each internal array hold objects with the same property value. In your example you could call:
[[self class] addressesForBusiness:someBusiness sectionProperty:addressLine];