How would I simplify this using (ideally) a single predicate with key-value coding collection operators? (The array of interest in the end is filteredGames.)
NSManagedObjectContext *context;
NSFetchRequest *request = [[NSFetchRequest alloc] init];
[request setEntity:[NSEntityDescription entityForName:#"Game" inManagedObjectContext:context];
NSArray *games = [context executeFetchRequest:request error:nil];
NSMutableArray *filteredGames = [[NSMutableArray alloc] init];
for (Game *game in games) {
NSInteger maxRoundNumber = [game.rounds valueForKeyPath:#"#max.number"];
Round *maxRound = [[game.rounds filteredSetUsingPredicate:[NSPredicate predicateWithFormat:#"number = %d", maxRoundNumber]] anyObject];
if (maxRound.someBoolProperty)
[filteredGames addObject:game];
}
Game has an NSSet property rounds of Rounds, and Round has an NSInteger property number, and I'm looking for those Games whose highest-number Round has some BOOL property someBoolProperty.
This seems to do what you want:
NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:#"Game"];
NSPredicate *predicate = [NSPredicate predicateWithFormat:#"ANY SUBQUERY(rounds, $r, $r.someBoolProperty = YES).number = #max.rounds.number"];
Related
i have list of brands stored in Core Data, each brand is associated with multiple contents. The contents have a flag called downStatus which is used to denote whether a content is downloaded or not. The following method is used to fetch all the brands from Core data sorted with brand name
-(void)getDownloadedBrands{
AppDelegate *aAppDelegate = (AppDelegate *)[UIApplication sharedApplication].delegate;
NSMutableArray *aBrands = [[NSMutableArray alloc] init];
NSEntityDescription *entity =
[NSEntityDescription entityForName:#"Brand" inManagedObjectContext:aAppDelegate.managedobjectcontext];
NSFetchRequest *request = [[NSFetchRequest alloc] init];
[request setEntity:entity];
NSSortDescriptor *sort=[[NSSortDescriptor alloc]initWithKey:#"brandName" ascending:YES];
//NSSortDescriptor *sort1=[[NSSortDescriptor alloc]initWithKey:#"downStatus" ascending:YES];
[request setSortDescriptors:[NSArray arrayWithObjects:sort, nil]];
aBrands =(NSMutableArray *)[aAppDelegate.managedobjectcontext executeFetchRequest:request error:nil];
[request release];
[sort release];
NSLog(#"%#",aBrands);
brands = [[NSMutableArray alloc]initWithArray:aBrands];
aAppDelegate.dbBrandArr = brands;
[self loadGridView];
}
Now i want to sort using the downStatus which is in the Content. So it will be like, downloaded brands in Alphabetical Order and then Un-Downloaded brands in Alphabetical order. The downStatus takes two values 1 for downloaded 0 for not downloaded. Please help.
One way to do it is by making 2 fetchRequests to CoreData using the NSPredicate with value 1/0 on downStatus property and using the same alphabetical sortDescriptor.
Now create a new Array by adding the 0 array to the 1 array. In your code it would look something like this:
-(void)getDownloadedBrands{
AppDelegate *aAppDelegate = (AppDelegate *)[UIApplication sharedApplication].delegate;
//2 arrays
NSMutableArray *aBrands0 = [[NSMutableArray alloc] init];
NSMutableArray *aBrands1 = [[NSMutableArray alloc] init];
//set entity en make requests
NSEntityDescription *entity = [NSEntityDescription entityForName:#"Brand" inManagedObjectContext:aAppDelegate.managedobjectcontext];
NSFetchRequest *request0 = [[NSFetchRequest alloc] init];
NSFetchRequest *request1 = [[NSFetchRequest alloc] init];
[request0 setEntity:entity];
[request1 setEntity:entity];
//create sortDescriptor alphabetically
NSSortDescriptor *sort=[[NSSortDescriptor alloc]initWithKey:#"brandName" ascending:YES];
//create predicates on downStatus property
NSPredicate *predicate0 = [NSPredicate predicateWithFormat:#"downStatus == %#", [NSNumber numberWithBool:0]];
NSPredicate *predicate1 = [NSPredicate predicateWithFormat:#"downStatus == %#", [NSNumber numberWithBool:1]];
//set predicates to the requests
[request0 setPredicate:predicate0];
[request1 setPredicate:predicate1];
//set sortDescriptor to both requests
[request0 setSortDescriptors:[NSArray arrayWithObjects:sort, nil]];
[request1 setSortDescriptors:[NSArray arrayWithObjects:sort, nil]];
//fetch arrays with downStatus 1/0
aBrands0 =(NSMutableArray *)[aAppDelegate.managedobjectcontext executeFetchRequest:request0 error:nil];
aBrands1 =(NSMutableArray *)[aAppDelegate.managedobjectcontext executeFetchRequest:request1 error:nil];
//release requests // NOT USING ARC??
[request0 release];
[request1 release];
[sort release];
//log results
NSLog(#"aBrands0: %#",aBrands0);
NSLog(#"aBrands1: %#",aBrands1);
//add object 0 array to 1 array
NSArray *combinedArray = [aBrands1 arrayByAddingObjectsFromArray:aBrands0];
//copy array to brands
brands = [[NSMutableArray alloc]initWithArray:combinedArray];
//set property on appDelegate
aAppDelegate.dbBrandArr = brands;
//reload tableView
[self loadGridView];
}
-- edit, adding answer for NSDictionary with downStatus key
-(void)getDownloadedBrands{
AppDelegate *aAppDelegate = (AppDelegate *)[UIApplication sharedApplication].delegate;
NSMutableArray *aBrands = [[NSMutableArray alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:#"Brand" inManagedObjectContext:aAppDelegate.managedobjectcontext];
NSFetchRequest *request = [[NSFetchRequest alloc] init];
[request setEntity:entity];
NSSortDescriptor *sort=[[NSSortDescriptor alloc]initWithKey:#"brandName" ascending:YES];
//NSSortDescriptor *sort1=[[NSSortDescriptor alloc]initWithKey:#"downStatus" ascending:YES];
[request setSortDescriptors:[NSArray arrayWithObjects:sort, nil]];
aBrands =(NSMutableArray *)[aAppDelegate.managedobjectcontext executeFetchRequest:request error:nil];
NSMutableArray *aBrands0 = [[NSMutableArray alloc] init];
NSMutableArray *aBrands1 = [[NSMutableArray alloc] init];
for (NSDictionary *dict in aBrands) {
if ([dict valueForKeyPath:#"downStatus"] == YES)
{
//add to 1 array
[aBrands1 addObject:dict];
}
else
{
//add to 0 array
[aBrands0 addObject:dict];
}
}
//sort arrays
NSArray * array1 = [aBrands1 sortedArrayUsingDescriptors:[NSArray arrayWithObject:sort]];
NSArray * array0 = [aBrands0 sortedArrayUsingDescriptors:[NSArray arrayWithObject:sort]];
NSArray * allArray = [aBrands1 arrayByAddingObjectsFromArray:aBrands0];
//combine arrays
//copy array to brands
brands = [[NSMutableArray alloc]initWithArray:combinedArray];
//set property on appDelegate
aAppDelegate.dbBrandArr = brands;
//reload tableView
[self loadGridView];
[request release];
[sort release];
NSLog(#"%#",aBrands);
}
If you plan to use the fetch result in a UITableViewController, you could use the sectionNameKeyPath of your fetchedResultsController for the downStatus and keep your sort descriptor for the brand name. Can look like this:
NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc]
initWithFetchRequest:fetchRequest managedObjectContext:self.managedObjectContext
sectionNameKeyPath:#"customSectionTitle" cacheName:nil];
Place this in the header file of your NSManagedObject :
-(NSString*)customSectionTitle;
And this in .m :
-(NSString*)customSectionTitle{
if ([downStatus boolValue] == YES) {
return #"Downloaded";
}
else {return #"Not Downloaded";}
}
If you do not plan to use a fetchedResultsController, just sort first by downStatus and then by brand name.
If I've created an NSFetchRequest on the main thread like so:
NSManagedObject *bar = ...;
NSFetchRequest *fetchRequest = [NSFetchRequest fetchRequestWithEntityName:#"Foo"];
[fetchRequest setPredicate:[NSPredicate predicateWithFormat:#"SELF.bar == %#",
[bar objectID]]];
Is it safe to pass this NSFetchRequest with an NSPredicate that contains a NSManagedObjectID to a background thread like so?
NSManagedObject *bar = nil;
NSFetchRequest *fetchRequest = [NSFetchRequest fetchRequestWithEntityName:#"Foo"];
[fetchRequest setPredicate:[NSPredicate predicateWithFormat:#"SELF.bar == %#",
[bar objectID]]];
NSPersistentStoreCoordinator *persistentStoreCoordinator = ...;
[[NSBlockOperation blockOperationWithBlock:^{
NSManagedObjectContext *managedObjectContext = [NSManagedObjectContext new];
[managedObjectContext setPersistentStoreCoordinator:persistentStoreCoordinator];
NSArray *foos = [managedObjectContext executeFetchRequest:fetchRequest
error:NULL];
}] start];
I found some example code in the CoreData release notes for iOS 5 that pretty much does this, so it looks ok.
NSFetchRequest *fr = [NSFetchRequest fetchRequestWithEntityName:#"Entity"];
__block NSUInteger rCount = 0;
[context performBlockAndWait:^() {
NSError *error;
rCount = [context countForFetchRequest:fr error:&error];
if (rCount == NSNotFound) {
// Handle the error.
}
}];
NSLog(#"Retrieved %d items", (int)rCount);
I'm using Core Data to store entities in the form
TrackerEntry
username
timestamp
I want to select the latest record for each user. Using sql it would be something like
SELECT MAX(timestamp) FROM Log GROUP BY username
Is there anyway to create an NSPredicate to do this?
I would do it using NSExpression. This bit of code below won't work for you because you will have to group by username too, but it's a start for the best way of doing this without having to fetch everything. You want to perform the max and group in the db, not in memory - as it will be faster:
NSFetchRequest *fetchRequest = [[[NSFetchRequest alloc] init] autorelease];
// Expression for the max
NSExpression *keyPathExpression = [NSExpression expressionForKeyPath:#"timestamp"];
NSEntityDescription *entity = [NSEntityDescription entityForName:entityName
inManagedObjectContext:self.coreDataStack.managedObjectContext];
[fetchRequest setEntity:entity];
[fetchRequest setResultType:NSDictionaryResultType];
NSExpression *valueSumExpression = [NSExpression expressionForFunction:#"max:" arguments:[NSArray arrayWithObject:keyPathExpression]];
NSExpressionDescription *expressionDescription = [[[NSExpressionDescription alloc] init] autorelease];
[expressionDescription setName:#"maxTimestamp"];
[expressionDescription setExpression:valueSumExpression];
[expressionDescription setExpressionResultType:NSDecimalAttributeType];
[fetchRequest setPropertiesToFetch:[NSArray arrayWithObject:expressionDescription]];
// Filter
//NSPredicate *pred = [NSPredicate predicateWithFormat:#" your predicate here"];
//fetchRequest.predicate = pred;
NSArray *results = [self.coreDataStack.managedObjectContext executeFetchRequest:fetchRequest error:nil];
if([results count] == 0) {
} else {
// [[results objectAtIndex:0] valueForKey:#"maxTimestamp"];
}
This worked for me, but it is a loop. First you have to get the unique names into an array.
NSFetchRequest *nameRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:#"Log" inManagedObjectContext:self.managedObjectContext];
nameRequest.entity = entity;
nameRequest.resultType = NSDictionaryResultType;
[nameRequest setPropertiesToFetch:[NSArray arrayWithObject:[[entity propertiesByName] objectForKey:#"name"]]];
NSArray *allNames = [self.managedObjectContext executeFetchRequest:nameRequest error:nil];
names = [allNames valueForKeyPath:#"#distinctUnionOfObjects.name"];
[nameRequest release];
NSLog(#"%#", names);
Not very efficient or convenient. After all, Core Data is not a database but an object graph.
Then you can loop through these and fetch just the top one.
NSMutableArray *mutableResults = [NSMutableArray array];
NSFetchRequest *request = [[NSFetchRequest alloc] init];
request.entity = [NSEntityDescription entityForName:#"Log" inManagedObjectContext:self.managedObjectContext];
NSSortDescriptor *numberSort = [NSSortDescriptor sortDescriptorWithKey:#"number" ascending:NO];
request.sortDescriptors = [NSArray arrayWithObject:numberSort];
request.fetchLimit = 1;
for (NSString *s in names) {
NSPredicate *pred = [NSPredicate predicateWithFormat:#"name = %#", s];
request.predicate = pred;
NSArray *results = [self.managedObjectContext executeFetchRequest:request error:nil];
[mutableResults addObject:[results objectAtIndex:0]];
}
[request release];
NSLog(#"%#", mutableResults);
I'm crashing with this message :
'NSInvalidArgumentException', reason: 'keypath name not found in entity
Obvisouly I'm not querying my entity correctly .
//fetching Data
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSManagedObjectContext *context = [(AppDelegate *)[[UIApplication sharedApplication] delegate] managedObjectContext];
NSEntityDescription *entity = [NSEntityDescription entityForName:#"Viewer" inManagedObjectContext:context];
[fetchRequest setEntity:entity];
NSString *attributeName = #"dF";
NSPredicate *predicate = [NSPredicate predicateWithFormat:#"name like %#",attributeName];
[fetchRequest setPredicate:predicate];
NSLog(#"predicate : %#",predicate);
NSError *error;
NSArray *items = [context executeFetchRequest:fetchRequest error:&error];
NSLog(#"items : %#",items);
[fetchRequest release];
//end of fetch
And here is my data Model:
I want to return the value of "dF", shouldn't call it like this ? :
NSString *attributeName = #"dF";
NSPredicate *predicate = [NSPredicate predicateWithFormat:#"name like %#",attributeName];
If you want to get value from your dF property, you have to fetch an array of NSManagedObjects and then use [fetchedManagedObject valueForKey:#"dF"]; to get your value.
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSManagedObjectContext *context = [(AppDelegate *)[[UIApplication sharedApplication] delegate] managedObjectContext];
NSEntityDescription *entity = [NSEntityDescription entityForName:#"Viewer" inManagedObjectContext:context];
[fetchRequest setEntity:entity];
NSArray *items = [context executeFetchRequest:fetchRequest error:&error];
[fetchRequest release];
NSManagedObject *mo = [items objectAtIndex:0]; // assuming that array is not empty
id value = [mo valueForKey:#"dF"];
Predicates are used to get array of NSManagedObjects that satisfy your criteria. E.g. if your dF is a number, you can create predicate like "dF > 100", then your fetch request will return an array with NSManagedObjects that will have dF values that > 100. But if you want to get just values, you don't need any predicate.
I was using a NSSortDescriptor initialized with a String key:
let fetchRequest = NSFetchRequest<SomeManagedObject>(entityName: "SomeManagedObject")
let sortDescriptor = NSSortDescriptor(key: "name", ascending: true)
fetchRequest.sortDescriptors = [sortDescriptor]
I then changed the name of the name attribute in the model. Refactored all of the property names, but didn't catch the stringly typed key: "name".
The solution for Swift is to use NSSortDescriptor(keyPath: instead, which will fail to compile if the property key path changes.
NSSortDescriptor(keyPath: \SomeManagedObject.firstName, ascending: true)
I've got a Core Data entity called "Card" which has a relationship "info" to another entity, "CardInfo". It's a one-to-many relationship: each card can have multiple CardInfos, but each CardInfo only has one Card.
The CardInfo entity just has two strings, "cardKey" and "cardValue". The object is to allow for arbitrary input of data for cards. Say, you wanted to know what color a card was. Then you added a CardInfo to each Card that had a cardKey of "color" and a cardValue of "black" or "red".
My general question is: what's the best way to get the set of Cards where each Card has a CardInfo where the CardKey and CardValue has specific values. For example: all Cards with relationship to CardInfo cardKey='color' and cardValue='red'? Ideally, I return an NSSet of all the appropriate Card * objects.
The loop at the end is not needed. A simple KVC call will clean it up nicely.
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
[fetchRequest setEntity:[NSEntityDescription entityForName:#"CardInfo" inManagedObjectContext:self.managedObjectContext]];
[fetchRequest setPredicate:[NSPredicate predicateWithFormat:#"cardKey = %# AND cardValue = %#", thisKey, thisValue]];
NSError *error = nil;
NSArray *items = [[self managedObjectContext executeFetchRequest:fetchRequest error:&error];
[fetchRequest release], fetchRequest = nil;
NSAssert1(error == nil, #"Error fetching objects: %#\n%#", [error localizedDescription], [error userInfo]);
return [items valueForKeyPath:#"#distinctUnionOfObjects.card"];
This is the answer that I came up with, but the two-part process seems inefficient to me. I figure there must be a more elegant way to do this with key-values or something
-(NSSet *)cardsWithCardKey:(NSString *)thisKey cardValue:(NSString *)thisValue {
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:#"CardInfo"
inManagedObjectContext:self.managedObjectContext];
[fetchRequest setEntity:entity];
NSPredicate *predicate = [NSPredicate
predicateWithFormat:#"(cardKey=%#) AND (cardValue=%#)",
thisKey,thisValue];
[fetchRequest setPredicate:predicate];
NSError *error;
NSArray *items = [self.managedObjectContext
executeFetchRequest:fetchRequest error:&error];
[fetchRequest release];
NSMutableSet *cardSet = [NSMutableSet setWithCapacity:[items count]];
for (int i = 0 ; i < [items count] ; i++) {
if ([[items objectAtIndex:i] card] != nil) {
[cardSet addObject:[[items objectAtIndex:i] card]];
}
}
return [NSSet setWithSet:cardSet];
}