NSFetchedResultsController - Core Data | Apple Developer Documentation
However, I didn't mention relationships in that discussion. Core Data and Swift: NSFetchedResultsController. In the previous article, we. Ad Summary: Adding a relationship after a save does not update NSFetchedResultsController that uses a predicate containing this relationship. If you're using Core Data, combining an NSFetchedResultsController and a UITableView provides a powerful way to display data from your.
It even offers the ability to use an in-memory cache to improve performance. Even though the NSFetchedResultsController class was designed with table views in mind, it also works great with collection views.
In this tutorial, we build a basic notes application that keeps track of your notes. We first need to create a project, set up the Core Data stack, and design the data model.
Set Language to Swift and Devices to iPhone. Make sure the checkboxes at the bottom are unchecked.
The demo app
Name the data model Notes and click Create. Attributes We need to add one entity to the data model, Note. The entity has four attributes: The bodies of the actions can remain empty for now. Add a bar button item to the navigation bar of the view controller and set System Item to Add in the Attributes Inspector. Open the Object Library and add a view controller.
Set its class to AddNoteViewController in the Identity Inspector and embed the view controller in a navigation controller. Add a bar button item on each side of the navigation bar, setting System Item to Cancel and Save respectively. Add a text field to the view controller, pin it to the top with constraints, and wire it up to the view controller's titleTextField outlet.
objective c - NSFetchedResultsController with relationship not updating - Stack Overflow
The add note view controller isn't responsible for creating a note. It delegates this task to a delegate. At the top of AddNoteViewController. Because the add note view controller is embedded in a navigation controller, we need to jump through a few hoops to get a hold of the add note view controller. This means we need an instance of the CoreDataManager class.
Add a property of type CoreDataManager and initialize an instance. But the API is intuitive and concise, and once you understand the Core Data stack, it starts to make sense, and you can quickly adapt to it. The most common mistake, is to start using the Core Data without understanding how its pieces fit together and relate to each other. The Core Data Stack The Core Data stack handles all of the interactions with the external data store and consists of three primary tools: It may sounds like a lot of pieces to be used, but since you setup all this parts, you will not need to make much changes, and you will be using mostly only the Managed Object Context.
The Managed Object Model, describes the schema that you will be using in your application. In Xcode, by selecting this.
How Not To Fight NSFetchedResultsController and Core Data
The Persistence Coordinator verifies that the data is in a consistent state that matches the definition on the model layer, and is responsible for extracting instances of entities from that data. For example add a new attribute to a entity, and re-run the application with previous stored data.
In this situation, you have two options. You can prepare a migration, if you already have your application on the App Store. And finally the Managed Object Context, which is the one that your source code will be interacting with the most, is responsible for managing objects created and returned using Core Data.
For object graph changes that affect multiple objects, it is much faster if they are already in memory, rather than searching for them again in the database. You can modify those objects however you like, and unless you actually save those changes, the persistent store remains unaltered.
And by tracking changes, the context is able to provide undo and redo support for you. After you create your project, you will find the. Go ahead and select that file to open the Xcode Data Model editor as shown below.
Go ahead and click that option to create a new entity. You can change the name like you would change a file name on Finder, but you can also use the inspector to perform this change.
Radar: NSFetchedResultsController does not get refreshed for added relationship | Cocoanetics
After you press enter, the Class name, below the section Entity, will also be updated with the desired name.
Every time a property affecting a todo's displayed section changes such as priority or done statusthe section identifier must be updated. In Objective-C we could accomplish this with property overrides or KVO but unfortunately neither of these techniques are easily available for managed objects in Swift as of Xcode 6 beta 5.
Instead we have to remember to manually trigger an update when doing drag 'n' drop or marking a todo as done. We get around this by assigning the sectionNameKeyPath to a Swift enum value with a method for getting the actual display name. This way, we achieve arbitrary sorting of sections. If we wanted to make the order of the sections dynamic, we could instead of using an enum, generate an identifier string runtime. This could as well have been stored in NSUserDefaults or just in memory using state restoration between app launches.
- Your Answer
- Context is everything with Core Data. No pun intended.
- Setting Up the Project
But since it affects the section identifier of the meta data objects, I found it suitable to have it connected in the persistent store. The reason is that this is where our sorting keys and sectionNameKeyPath are stored.
The fetched results controller can be setup with key paths directing to a related entity, but it only keeps track of changes on its original fetched dataset. Since the meta data object has a one to one relationship to the real ToDo object, we can easily extract the todo once we have the metadata.
To make this perform better, we add "toDo" to the relationshipKeyPathsForPrefetching property of the fetch request. Else, CoreData would fire a fault to the persistent store for every single todo once they are displayed in the table view. The fetched results controller delegate calls which notify of changes to sections and objects are forwarded to a separate FetchControllerDelegate class, which uses an implementation mostly like the example found in the developer library.
It responds to the delegate calls by informing the table view.