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Fetch Core Data entity with a filtered set of child elements based on a property


Fetch Core Data entity with a filtered set of child elements based on a property

By : user2955228
Date : November 22 2020, 10:38 AM
this one helps. Welcome to Core Data. The way this works is a follows:
First fetch the playlists. They have a to-many relationship with songs no matter if they are deleted of not. The removed property is not in the Playlist entity, so it does not matter when fetching playlists.
code :
let validSongs = aPlaylist.songs.filteredSetUsingPredicate(
   NSPredicate(format: "removed = false")
) 
func validSongs() -> NSSet {
   if !self.songs.count {  return NSSet()  }
   return self.songs.filteredSetUsingPredicate(
      NSPredicate(format: "removed = false")
   ) 
}
aPlaylist.validSongs


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Core Data - How to fetch an entity with max value property

Core Data - How to fetch an entity with max value property


By : herodolphin
Date : March 29 2020, 07:55 AM
Any of those help You set the fetchLimit to 1 and sort by personId in descending order. E.g.:
code :
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] initWithEntityName:@"Person"];

fetchRequest.fetchLimit = 1;
fetchRequest.sortDescriptors = @[[NSSortDescriptor sortDescriptorWithKey:@"personId" ascending:NO]];

NSError *error = nil;

id person = [managedObjectContext executeFetchRequest:fetchRequest error:&error].firstObject;
Trying to fetch results in Core Data based on Entity's relationship object in iOS

Trying to fetch results in Core Data based on Entity's relationship object in iOS


By : anthony sanchez
Date : March 29 2020, 07:55 AM
Does that help The predicate should name the actual relationships involved, not the names of the entities.
ie:
code :
[NSPredicate predicateWithFormat:@"relationshipNameToEntityB.relationshipNameToEntityC.attributeNameOnEntityC == %@", filter];
Core Data: How to fetch Entities based on an attribute of a related entity

Core Data: How to fetch Entities based on an attribute of a related entity


By : user3325866
Date : March 29 2020, 07:55 AM
Fetch objects from Core Data where a filtered relationship is empty

Fetch objects from Core Data where a filtered relationship is empty


By : whoisjordi
Date : March 29 2020, 07:55 AM
Any of those help I managed to figure it out based on some other posts talking about SUBQUERY
code :
NSPredicate *predicate = [NSPredicate predicateWithFormat:
    @"SUBQUERY(shifts, $x, %@ <= $x.startDate and $x.startDate <= %@).@count == 0",
    beginningOfDateRange, endingOfDateRange);
Swift: Sorting Core Data child entities on fetch based on Date

Swift: Sorting Core Data child entities on fetch based on Date


By : Sridhar Chandrasekar
Date : March 29 2020, 07:55 AM
wish helps you Some notes:
Basically you cannot sort dates in string format "yyyy dd MM", either use "yyyy MM dd" or – highly recommended – Date type. You cannot sort a relationship in place. To-many relationships are Sets which are unordered. By the way declare the relationship as native Set rather than unspecified NSSet and as non-optional. Don't use a compound predicate, use one predicate and don't fetch DateKey records, fetch CalendarEventModel records with predicate dateKey.dateInfo >= startDate && dateKey.dateInfo <= endDate and add there the two sort descriptors.
code :
let calendar = Calendar.current
let now = Date()
let nowPlus9Days = calendar.date(byAdding: .day, value: 9, to: now)!
let startDate = calendar.startOfDay(for: now)
let endDate = calendar.startOfDay(for: nowPlus9Days)
let predicate = NSPredicate(format: "dateKey.dateInfo >= %@ && dateKey.dateInfo <= %@", startDate as CVarArg, endDate as CVarArg)
let sortDescriptors = [NSSortDescriptor(key: "startDate", ascending: true), NSSortDescriptor(key: "isAllDay", ascending: true)]

let eventFetch : NSFetchRequest<CalendarEventModel> = CalendarEventModel.fetchRequest()
eventFetch.predicate = predicate
eventFetch.sortDescriptors = sortDescriptors
do {
    let fetchResultsArray = try coreDataContext.fetch(eventFetch)
    let groupedDictionary = Dictionary(grouping: fetchResultsArray, by: {$0.startDate})

} catch {
    print("Core Data initial fetch failed in Calendar Controller: \(error)")
}
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