Each of these relationships are set up as a one-to-one relationship. In this article, we will go even further to see how we can store an array of custom data types in Core Data with Transformable and NSSecureCoding. Codable CoreData Posted on 20 October 2017. There is a relationship between them - each Formation is assigned a single Board. Create a persistent container and point it to the xcdatamodeld — which matches the xcdatamodeld filename, container = NSPersistentContainer(name: “CoreDataUsingCodable”), Load the database if it exists, if not create it, container.loadPersistentStores { storeDescription, error in, // resolve conflict by using correct NSMergePolicy, self.container.viewContext.mergePolicy = NSMergeByPropertyObjectTrumpMergePolicy. For a simple example we can use the GitHub API, and this tutorial seeks to guide you through exactly that. In Bite 315 we started looking at the new Codable protocol in Swift 4.Today we'll learn how to work with Date types when encoding and decoding. Here’s the relevant parsing code: Let’s step through the salient points of the above code. tableView.register(UITableViewCell.self, forCellReuseIdentifier: “Cell”), We can create Codable models to store the data. Content discovery. We want to use core data to cache results from the Web. Repository dashboard. For an NSManagedObject subclass it's not that easy. Let’s go through them in detail. The JSON parsing method is part of a controller, UserController, that will take care of all the logic required for fetching the data representing our users from both the network and Core Data. 5 min read. Core Data is just a framework like UIKit. This means it has to conform to both the Decodable and Encodable protocols we will need to deal with passing the context around so the following extension, So we are required to provide encode, an initializer and here we declare our coding keys (because we are conforming to Codable, after all!). The second time, the saved store is attempted to be opened and the application crashes. This request is performed on the NSManagedObjectContext, and if this is successful the tableView is reloaded. Basically, we need to appropriately implement Encodable’s encode(to:) and Decodable’s init(from:). Undo and Redo of Individual or Batched Changes. As you know Core Data attributes can have properties like Undefined, Integer16, Integer32, Integer64, Float, Decimal, Date, Boolean, String, Double, Binary Data in Objective C has to offer. The NSPersistentContainer consists of a set of objects that facilitate saving and retrieving information from Core Data. Indeterminate Architecture: Scissor-Pair Transformable Structures . The image Data is Converted to and From an NSData Instance that contains the image’s PNG Representation .this is all handled transparently for you by a custom NSValueTransformer. Bocian67. There is more than one way to build an abstraction that fetches data from Core Data and updates your views as needed. FAQs . struct Spaceship: Codable {var name: String var createdAt: Date}. so we can potentially share this container elsewhere in the App. As I said you can't add a custom class or struct as a Core Data attribute, you have to use a transformable type which needs extra work to serialize and deserialize the objects. So each commit holds a url, html_url and sha as well as having a relationship with the committer and gitcommit (in all these cases inverse relationships are recommended, and it keeps this looking like any database). This is then saved to the Core Data store, which we then load back and populate the tableView with (so we don’t get duplicates we let core data manage the constraints, so obviously we have to read back from there! Abstraction of direct database handling. For this two work we need to make our class to conform to Codable. One way to achieve that is to store the context in the custom dictionary userInfo property of the Decoder instance. Go to the data model and add a new entity, renaming it to Commit. To get the crash the project must be run twice. The sample app I started from has only one simple model, User, illustrated below: In order to be able to store instance of Userin Core Data, a few changes are required. What is this magic type, and what does it transform into? Working with Codable and Core Data | by Andrea Prearo, Leverage the Codable protocol to easily parse the JSON response from the web service and create the appropriate model instance. The simplest way to achieve this is to delete, and re-create, Core Data database every time the app has network connection. For Core Data this means that the default ValueTransformer, which uses NSCoding to transform a custom data type into a format that can be stored in the persistent store, at some point will change as well. The UserController requires a NSPersistentContainer instance to be initialized. and retrieve data saves the context using saveContext. In order to achieve that, I set the following goals: This task has been an interesting learning experience. In this post, I described my personal experience working with Codable and Core Data. This is a fairly ordinary retrieval of data from a url, but once the data is decoded we put the data into the NSManagedObject subclass (called Commit). Each commit is related to an object that contains the message (that is, the commit message). Before the actual parsing, though, we store the managed object context in the decoder userInfo dictionary using CodingUserInfoKey.managedObjectContext as the key: The managed object context instance we just stored in userInfo will be used by the User class while performing its decoding task (as described in the Allow seamless encoding/decoding with Core Data section above). Generates classes according to your CoreData model. Model contains relations and types of entities. There are a couple of notable built-in features such as 1. change tracking of data, 2. undo and redo to data 3. Core data binary store transformable attribute bug in iOS11 (Now resolved, see the Branch AppleFix) This xcode project demonstrates a bug in iOS 11 Core Data Binary stores. Let's dive in. Core Data typically decreases by 50 to 70 percent the amount of code you write to support the model layer. Broadly speaking, NSCoding is the Objective-C way of archiving data and Codable is the Swift way. To make Codable work with Core Data we need to conform to both Encodable and Decodable in a way that allows to correctly interact with the app persistent container. How to encode/decode Core Data NSSets with Relationships I have two classes: Board and Formation. With plain structs, you can conform your struct to Codable and you convert the struct from and to JSON data automatically. To make things easier we will provide a CodingUserInfoKey extension that conveniently wraps the key name: Now, we can easily refer to the key reserved to store the managed object context as CodingUserInfoKey.managedObjectContext. And of course we can now display the data on the table cells: Here is a GitHub link with the full implementation as described above: Want to get in contact? Once the parse method is successfully executed all the User instances retrieved from the JSON response will have been saved and will be accessible in our Core Data persistent storage. votes. Speciflcally, when you create subclasses of NSManagedObject, you can define the properties that the entity can use for code completion, and you can add convenience methods to … With the two above methods implemented, we now have everything we need to successfully interact with Core Data and our User instances. This will ensure we can access Core Data persistent container and its managed object context when needed. then call functions to retrieve data from the URL, and load saved data from core data. Transformable attributes in Core Data Boring: strings and integers; fun and mysterious: transformable! ios swift core-data codable. As usual, when using Codable, we create a JSONDecoder instance inside the parse method to parse the JSON response. In particular, we need to be able to access the persistent managed object context and correctly insert each entity (NSManagedObject) representing a User into Core Data (more on this in the Parsing the JSON response and storing users in Core Data section below). Create a new project, ticking the Use Core Data checkbox. NSSecureCoding and transformable properties in Core Data. In order to use Core Data to store our User instances we need to be able to access the persistent container and, in particular, the managed object context (viewContext) from the Decodable initializer implementation inside the model: Since we can’t change the signature of the above method, and explicitly pass the required managed object context as a parameter, we have to find an alternative way to make the context available. Creating NSManagedObject Subclasses. A lot of work. Partial loading unlike UserDefaults. And specify UIColor (Or NSColor for OSX) in the class property type. Core Data’s undo manager tracks changes and can roll them back individually, in groups, or all at once, making it easy to add undo and redo support to your app. The Xcode warning disappeared, but everything seemed to work fine in the app (although the transformer was never used). CoreDataCodable framework provides a CoreDataEncoder and CoreDataDecoder to encode and decode Swift Codable types to CoreData NSManagedObject. About About CORE Blog Contact us. When I tested this, I had a typo in the Transformer Class name on the Core Data Model. For Codable types you will need to implement a couple protocols to provide the necesary information for CoreData serialization. 5. The code required to clear the storage is rather simple, as we just need to delete one table: In order to retrieve the stored User instances, the UserController provides the fetchFromStorage() method: Both methods perform their respective task by means of a NSFetchRequest. Why Core Data? Recommender Discovery. Codable: An API to help encode and decode data to/from a serialized format, Be able to build a UITableView (although the steps are run through as reminder bullet points here), Some knowledge of Core Data, and be able to set up a simple Core Data project, The datasource will be an array of NSManagedObject, Connect the datasource and delegate to the view controller be control-dragging from the table view to the view controller in interface builder, Include an outlet for tableView from the storyboard to the view controller, Create the standard functions for a UITableViewDataSource, and make the ViewController conform to the UITableViewDataSource protocol, Assign the NSManagedObjectContext to the decoder. We are putting data into a Codable model, and then converting this to a subclassed NSManagedObjectModel. By default, Core Data returns NSManagedObject instances to your application. 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