And you know what happened next. What does that mean? If you're serious about Core Data, check out Mastering Core Data With Swift. Fortunately for us, a few clever engineers at Apple have created a solution to safely … To add support for lightweight migrations to the CoreDataManager class, we need to make a minor change. Basically the Core data migration happens in three steps: 1) Core data copies all objects from initial data store to the next. Note that there are a few caveats you should be aware of. Open the project's data model by selecting Lists.xcdatamodeld in the Project Navigator. In the Data Model Ins… You should never modify a data model without telling Core Data about the changes you made. It's time to create a new version of the data model. Make sure that the project that you intend to migrate builds successfully in Swift 4 or Swift … Let's start with a clean slate by opening Done.xcdatamodeld and removing the updatedAt attribute from the Item entity. If it finds one, Core Data makes sure the data model is compatible with the persistent store. Looking for something to help kick start your next project? Heavy migrations are a bit trickier. This class will tell Core Data how to map the old boolean value to the new integer value. In the previous articles of this series, we've encountered an annoying issue that we need to address. How would you feel if an airline lost your luggage, pretending as if nothing happened. Bart Jacobs runs Code Foundry, a mobile development company based in Belgium and writes about iOS and Swift development on Cocoacasts. The data layer of a software project requires care, attention, and preparation. The changes you can make to a data model with lightweight migrations are limited. Versioning and migrations go … Don't forget to also add the user relationship to the List entity. What we haven't told Core Data is what it should do if it runs into an incompatibility issue. In the Data Model Inspector, set Type to To Many. The application should run and work just fine. The first key, NSMigratePersistentStoresAutomaticallyOption, tells Core Data that we'd like it to attempt to migrate the persistent store for us. If a Core Data project has any kind of complexity, then subclassing NSManagedObject is the way to go. Near the end, Core Data tells us that the data model that was used to open the persistent store is incompatible with the data model that was used to create the persistent store. If you've worked with Ruby on Rails or any other framework that supports migrations, then Core Data migrations will make a lot of sense to you. Before we change this, though, we need to tell Core Data what it should do with the versioned data model. The words lightweight and heavy are pretty descriptive, but it's important that you understand how Core Data handles each type of migration. Run the application one more time and notice how the application crashes as soon as it's launched. This will take you to the data model in the Xcode project. You can see the .xcdatamodeld file as a package for the versions of the data model, with each version represented by an .xcdatamodel file. The implementation of applicationIncompatibleStoresDirectory() is similar to that of applicationStoresDirectory(). Contribute to tutsplus/CoreDataSwift-Migrations development by creating an account on GitHub. In the implementation of the persistentStoreCoordinator property, we create the persistent store coordinator and add a persistent store to it by invoking addPersistentStoreWithType(_:configuration:URL:options:). An application that grows and gains features also gains new requirements. As we saw earlier, adding an attribute, updatedAt, to the Item entity results in the persistent store being incompatible with the modified data model. Lightweight migrations are relatively powerful and they are easy to implement, but that doesn't mean you can modify the data model at any time. I cannot stress enough how important this phase of a project is. Add two attributes to the Userentity: 1. firstName of type String 2. lastName of type String Add a relationship, lists, to the User entity and set its destination to the List entity. Add a method to the subclass to convert the value. Core Data and Unit Testing haven't always been the best of friends. A migration manager instance that performs a migration of data from one persistent store to another using a given mapping model. Core Data inspects the versioned data model to understand how the persistent store relates to the data model. The data model, for example, grows and changes. Note that we remove the key-value pair when the user taps the button of the alert. Core Data is Apple’s object graph management and persistency framework. Design templates, stock videos, photos & audio, and much more. Core Data tells us that the data model is not compatible with the data model we used to create the persistent store. Core Data allows us to version the data model and this enables us to safely modify the data model. With the data model selected, choose Add Model Version... from the Editor menu. A mapping model needs a source and a destination data model. When a data model change is introduced, the developer uses EF Core tools to add a corresponding migration describing the updates necessary to keep the database schema in sync. Migrations are great, but they should be used sparingly. I already told you that a persistent store is tied to a particular version of the data model. Crashes are no problem during development, but they are catastrophic in production. GitHub Gist: instantly share code, notes, and snippets. A small triangle has appeared on the left of the data model in the Project Navigator. You can download the source files of the tutorial from GitHub. In this tutorial, we take a look at how Core Data helps us manage changes of the data model and what pitfalls we absolutely need to avoid. Are you still running into a crash? Design, code, video editing, business, and much more. Collaborate. Run the application again. In the next section, we take a closer look at what this means and how to prevent crashes due to a problematic migration. Whenever we modify the data model of a Core Data applicati. Trademarks and brands are the property of their respective owners. Did that crash take you by surprise? Envato Tuts+ tutorials are translated into other languages by our community members—you can be involved too! Finding out the cause of the crash is easy. How this works becomes clear in a moment. Select the List entity and create a To One relationship with the User entity as its destination. Core Data includes mechanisms for versioning your data model and migrating user data as your app evolves. Give the subclass an obvious name like ModelMigration1to2. If the data model changes, we need to tell Core Data how to migrate the data of the persistent store to the new data model version. I strongly recommend that you choose a lightweight migration over a heavy migration whenever you can. To be clear, the abort function causes the application to terminate immediately. Run the application to see if we solved the incompatibility problem we ran into earlier. A simple example of something that goes beyond … - Selection from Core Data in Swift [Book] Swift — 4 — Core Data, We are done with core data migration. In other words, we need to hand Core Data the necessary information to migrate the persistent store from one version of the data model to another. Because heavy migrations are a complex topic, we won't cover it in this series. Select Done.xcdatamodeld in the Project Navigator and open the File Inspector on the right. When it comes to structured data persistence, Core Data is an obvious choice. Also to address new changes we should not make any changes in existing data model. The idea is simple. Even if the data model is incompatible with the persistent store, you may be able to recover data form it. Let me rephrase that. By looking at the versioned data model, it also knows if the persistent store needs to be migrated before it can be used with the current version of the data model. It's time to create a new persistent store to finish the setup of the Core Data stack. Add a new attribute to the Item entity in Done 2.xcdatamodel and run the application one more time. © 2021 Envato Pty Ltd. Hello readers. Core Data handles changes pretty well as long as you play by the rules of the framework. Let's revisit the to-do application we created in the previous article. It keeps a reference to the identifier of the data model. Lead discussions. The assistant can also be invoked manually from the menu Edit -> Convert -> To Current Swift Syntax… You can choose from two kinds of migration to perform: Use Swift 2.3 Modifies your project to enable the Use Legacy Swift build setting and provides source changes to be able to build against the new SDKs. If Core Data detects that the persistent store is incompatible with the data model, we first move the incompatible store to a safe location. Master the Core Data in Swift 4.2 and iOS 12, and take your iOS development skills to the next level. Open Done.xcdatamodeld and add an attribute updatedAt of type Date to the Item entity. Versioning and migrations go hand in hand. Done.Xcdatamodel and Done 2.xcdatamodel should now have a green checkmark before shipping a new model... Application 's data model relate to one relationship with the user relationship to 2.xcdatamodel. 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