nsfetchrequest

问题 How would I sort a NSFetchRequest with that the date property of the managed object. So that it creates a array with the dates going in order? Here is my code so far... var request : NSFetchRequest = NSFetchRequest(entityName: "History"); request.predicate = NSPredicate(format: "counts = %@", true) request.sortDescriptors = [???] <- What should I put here? var results : [NSManagedObject] = context.executeFetchRequest(request, error: nil) as [NSManagedObject] 回答1: // newest first request

问题 I have a core data DB with multiple entities. There is a parent entity called "Person" which has many "Friends", "Friends" have many "Activities", and "Activities" have "Types" ("Types has a to-many relationship to "Activities"). What I'm trying to achieve is filtering all the "Person" entities by "Types". A user would be tapping on a "Type" and then I would refresh my table and filter the "Person" entities that are displayed by the "Types" that are associated with them. Currently I'm

问题 In my model, I have a Sale entity, each Sale entity has a date property (NSDate). I want to compute the sum of sales for each month. I know how to create the expression for computing the sum, what I want to find out is how do I tell NSFetchRequest to group by month. 回答1: You can use a NSFetchedResultsController to do the grouping for you. It has a parameter in the factory method called sectionNameKeyPath which you can use to separate your data. You will get all the NSIndexPath arithmetic for

问题 I am trying to process a lot of objects in chunks of a certain size (batchSize). This loop seems to work, but it processes only half the records. Relevant piece of code is: { //Prepare fetching products without images in the database NSFetchRequest * productFetchRequest = [NSFetchRequest fetchRequestWithEntityName:@"Product"]; //Sort by last changed photo first NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"photoModificationDate" ascending:NO]; [productFetchRequest

问题 I need to sort a bunch of objects based on an integer that is stored in an NSString . I know this is one solution and it works: NSSortDescriptor *mySortDescriptor = [NSSortDescriptor sortDescriptorWithKey: @"from" ascending: YES comparator:^(id obj1, id obj2) { if ([obj1 integerValue] > [obj2 integerValue]) { return (NSComparisonResult) NSOrderedDescending; } if ([obj1 integerValue] < [obj2 integerValue]) { return (NSComparisonResult) NSOrderedAscending; } return (NSComparisonResult)

问题 I have a one to many entity relationship between two entities: EntityP (Parent) <-->> EntityC (Child) Attributes and Relationships: EntityP.title EntityP.dateTimeStamp EntityP.PtoC (relationship) EntityC.title EntityC.dateTimeStamp EntityC.CtoP (relationship) // Can be used to get "one" EntityP record I use fetch results controller to show the results. Here's my implementation of the fetch results controller: #pragma mark - #pragma mark Fetched results controller - (NSFetchedResultsController

问题 So I am trying to get a UITableView to show a list of objects by section (thing.title), but list them in descending order by date. The table is is split into sections, which are labeled correctly (section headers are the different thing titles). But the objects in each section are only half correct. The objects in each section are listed in descending order, but some sections contain data that should be in other sections. An example of what is happening: <Header> Big Title Name <data><Big

问题 I have one entity & three Attribute called as item, rate, category. i want to filter value from category attribute. if (managedObjectContext==nil) { AppDelegate *appDelegate = (AppDelegate *)[UIApplication sharedApplication].delegate; managedObjectContext = appDelegate.managedObjectContext; } NSFetchRequest *request = [[NSFetchRequest alloc] init]; NSEntityDescription *entity = [NSEntityDescription entityForName:@"Restaurantmenu" inManagedObjectContext:managedObjectContext]; [request

问题 I am trying to create a fetchRequest that shows me all values that are not already in another array. This code returns the array I expect: NSArray *questionChoices = [self.currentQuestionChoiceGroup.questionChoices allObjects]; NSArray *filteredQuestionChoices = [questionChoices filteredArrayUsingPredicate:[NSPredicate predicateWithFormat:@"NONE %@ == code", myarr]]; myarr contains 1 item, and that 1 item is excluded from the filtered results, as expected. However, this code doesn't work:

问题 How to write NSPredicate to fetch the rows that matches with values in the array? E.g: [NSPredicate predicateWithFormat:@"UserName IN %@",UserIDArray]; If UserIDArray contains ID of users, how does one fetch the user name which matches with the values in this array? 回答1: Let me start with this advice. Core Data is not SQL. Entities are not tables. Objects are not rows. Columns are not attributes/properties. Core Data is an object graph management system that may or may not persist the object