core data migration swift

Make sure that the project that you intend to migrate builds successfully in Swift 4 or Swift … I have never come in a situation that warranted calling abort in production and it pains me when I browse a project in which Apple's default implementation for setting up the Core Data stack is used, in which abort is called when adding a persistent store is unsuccessful. By running the application for the first time, Core Data automatically created a persistent store based on the data model of the project. Tag: core-data-migration. To solve the problem we're facing, we need to find a way to tell Core Data how one version of the data model relates to another version. To add support for migrations, we pass in a dictionary of options with two keys: What is a mapping model? We now understand the cause of this. When you downloaded or cloned the project from GitHub, I asked you to run the application to make sure everything was set up correctly. The implementation of applicationStoresDirectory(), a helper method, is straightforward as you can see below. That's the first step to a happy user. In this example, we have only one choice. Losing the user's data is one thing, but pretending that nothing happened isn't nice. It is also called light weight migration. Lightweight migrations require very little work from your part, the developer. This will take you to the data model in the Xcode project. This checkmark indicates what the current model version is, Done.xcdatamodel in this example. Heavy migrations are powerful, but that power comes at a cost. Lightweight migrations carry little overhead. NSMigrationManagercan infer the mapping model between two models. There are some limitations on how much you can change the data model, since this method requires the least amount of work, it’s preferred migration method. Questions? Developers are only human and we all make mistakes, but that doesn't mean you should throw in the towel and call abort. We are closing in on the root of the problem. Swift – Core Data – Part 3 Creating a Singleton Core Data & refactoring insert, update, delete operations; Swift – Core Data — Part 4 Writing unit test cases; Swift – Core Data — Part 5 Core Data Migration; Swift – Core Data — Part 6 Using NSFetchResultController with UITableView Run the application one more time and notice how the application crashes as soon as it's launched. The result of this action is that we can now see three data model files in the Project Navigator. The next few lines should look very familiar by now. If Core Data detects that the persistent store is incompatible with the data model, we first move the incompatible store to a safe location. To solve that problem, we first and foremost leave the data model that was used to create the persistent store untouched. Envato Tuts+ tutorials are translated into other languages by our community members—you can be involved too! For example, if you've set the data model version to Done 2.xcdatamodel, run the application, and then make changes to Done 2.xcdatamodel, then you'll most likely run into a crash due to the persistent store being incompatible with the data model. The implementation of showAlertWithTitle(_:message:cancelButtonTitle:) is similar to the one we've seen in the AddToDoViewController. If you don't invest time architecting the data model, chances are you run into problems that could have been avoided. Heavyweight migrations, however, are a pain. This dictionary of options includes instructions for Core Data. Note that I've changed the value of URLPersistentStore, the location of the persistent store. Because we reverted the data model to its original state, the application should no longer crash. In the development phase of a project we keep on adding new features in every versions of app. Note that a green checkmark is added to Lists.xcdatamodel. The error message in the console indicates that the data model that was used to create the persistent store is not identical to the current data model. Collaborate. We do this to make sure the user's data isn't lost. Design like a professional without Photoshop. You always need to test the migration to be sure. Select Lists 2.xcdatamodel and create the User entity we added earlier. Core Data allows us to version the data model and this enables us to safely modify the data model. pyrabbit / new_core_data_stack.swift. The goal of this tutorial is to prevent that adding the persistent store to the persistent store coordinator fails. Looking for something to help kick start your next project? A Heavy/Manual Migration A heavy migration is required when we go outside of the bounds of what a light migration can accomplish. However, because we changed the data model by adding an attribute to the Item entity, updatedAt, Core Data no longer understands how it should store Item records in the SQLite database. Read this paragraph again. A migration manager instance that performs a migration of data from one persistent store to another using a given mapping model. Open CoreDataManager.swift and inspect the implementation of the persistentStoreCoordinator property. That's not what we have in mind, though. For example, you could urge them to contact support and you can even implement a feature that lets them send you the corrupt store. Core Data is Apple’s object graph management and persistency framework. 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. The data model, for example, grows and changes. In the previous articles of this series, we've encountered an annoying issue that we need to address. Xcode 10.2 comes with a Swift Migrator tool that helps you migrate your project to Swift 5. If the persistent store coordinator is unable to add the existing persistent store at URLPersistentStore, we move the persistent store to a separate directory. If Core Data was unable to migrate the persistent store using the data model, we remember this by setting a key-value pair in the application's user defaults database. If you run into a crash, then you've done something wrong. We look for this key-value pair in the viewDidLoad() method of the ViewController class. For heavyweight migrations, the developer is responsible for creating the mapping model. Design templates, stock videos, photos & audio, and much more. With this change, we are ready to migrate the data model to the new version we created a few moments ago. A mapping model defines how one version of the data model relates to another version. 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. Remember that the inverse relationship of the lists relationship is automatically set for us by Core Data. If an app is using Core Data merely as an offline cache, when you update the app, you can simply delete and rebuild the data store. 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. Because heavy migrations are a complex topic, we won't cover it in this series. If the matching MOM isn’t flagged as the “current” MOM, data migration will then kick in. 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. Data migration in core banking is all about the seamless movement of entries, balances, P&L/balance sheet data, customer information, contracts, products, KYC details and other forms of financial/nonfinancial data from the source to the target system. Lightweight migrations are much easier because Core Data takes care of the heavy lifting for us. A small triangle has appeared on the left of the data model in the Project Navigator. So a while ago, I wrote on how I discovered the existence of this thing call Core Data migrations, by having my app crash when I added a new entity to my core data model.So the solution to that is actually not very hard, the only issue I had was that a majority of the solutions out there, deal with it in apps built with Objective-C and I needed a solution in Swift. Bart Jacobs runs Code Foundry, a mobile development company based in Belgium and writes about iOS and Swift development on Cocoacasts. It is fine to make incremental changes to the data model as your application grows, but once your application is in the hands of users you need to make sure they don't lose their data due to a problematic migration. It's time to verify that everything is still working. When is a migration necessary? The cost of a lightweight migration is substantially lower than that of a heavy migration. Core Data inspects the versioned data model to understand how the persistent store relates to the data model. Data Migration Services from Core DataCloud with DataDobi. Because we haven't run the application yet, we can still modify the new data model version without running into compatibility issues. Heavyweight migrations are pretty complex and you should try to avoid them whenever possible. And always test migrations before shipping a new version of your application. The goal of this article is to give you an overview of the Core Data architecture as well as to provide a list of basic operations together with working examples to help you get off to a quick start.. Core Data will then need a mapping model to understand how the versions of the data model relate to one another. Crashes are no problem during development, but they are catastrophic in production. Migrations let you safely modify your application's data model and, in the case of lightweight migrations, without much overhead. If you wish to understand how migrations work, you'll first need to understand how to version the Core Data data model. We also marked the new data model version as the active data model version. But how do you tell Core Data about the changes you make to a data model? Core Data Migration In order to follow core data migration we should keep on versioning our.xcdatamodeld file. Run the application in the simulator or on a physical device to make sure everything is set up correctly. Heavy migrations are a bit trickier. It's certainly more verbose than in Objective-C. Also note that I force unwrap the result of path() of the URL constant, because we can safely assume that there's an application support directory in the application's sandbox, both on iOS and on OS X. Did that crash take you by surprise? When we launched the application for the first time, Core Data created a SQLite database based on the data model. Versioning and migrations go … To do that, we make use of two more helper methods, applicationIncompatibleStoresDirectory() and nameForIncompatibleStore(). You should never modify a data model without telling Core Data about the changes you made. Created Mar 22, 2017. The idea is simple. It's therefore important to properly test what we've implemented in this article. Name the relationship user and set the inverse relationship to lists. © 2021 Envato Pty Ltd. In nameForIncompatibleStore(), we generate a name for the incompatible store based on the current date and time to avoid naming collisions. Because the existing persistent store is now incompatible with the data model, the incompatible persistent store is moved to the Incompatible subdirectory and a new persistent store is created. You can see the .xcdatamodeld file as a package for the versions of the data model, with each version represented by an .xcdatamodel file. We need to tell it to perform a migration. The easiest answer to this common question is “when you need to make changes to the data model.” However, there are some cases in which you can avoid a migration. Fortunately for us, a few clever engineers at Apple have created a solution to safely … Run the application to see if we solved the incompatibility problem we ran into earlier. GitHub Gist: instantly share code, notes, and snippets. Note that the green checkmark has moved from Lists.xcdatamodel to Lists 2.xcdatamodel. The first key, NSMigratePersistentStoresAutomaticallyOption, tells Core Data that we'd like it to attempt to migrate the persistent store for us. The answer is versioning. For example, a lightweight migration lets you add or rename attributes and entities, but you cannot modify the type of an attribute or the relationships between existing entities. There is one top level data model with a .xcdatamodeld extension and two children with a .xcdatamodel extension. In the previous articles of this series, we've encountered an annoying issue that we need to address. This makes it tempting to creat… When it comes to structured data persistence, Core Data is an obvious choice. In the Project Navigator, Done 2.xcdatamodel should now have a green checkmark instead of Done.xcdatamodel. Migrations are great, but they should be used sparingly. This step is probably the most important one in terms of creating a user friendly application. Avoid them whenever possible. Whenever we modify the data model of a Core Data applicati. In the next section, we take a closer look at what this means and how to prevent crashes due to a problematic migration. The changes you can make to a data model with lightweight migrations are limited. Even if the data model is incompatible with the persistent store, you may be able to recover data form it. Are you still running into a crash? With the data model selected, choose Add Model Version... from the Editor menu. You can download the source files of the tutorial from GitHub. As a result, Core Data bails out and throws an error. The fourth parameter of this method is a dictionary of options, which is currently nil. Along with Core Data versioning, migration and iCloud integration, I will take you on developing 5 iOS applications and how we can integrate all of these components into Core Data. Before we make any changes, select Lists.xcdatamodeld (not Lists.xcdatamodel), open the File Inspector on the right, and set Model Version to Lists 2, the data model version we created a moment ago. Do you remember that addPersistentStore(ofType:configurationName:at:options:) accepts a dictionary of options as its last parameter? 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. A mapping model needs a source and a destination data model. Finding out the cause of the crash is easy. Of course, the flip side of lightweight migrations is that they are less powerful than heavy migrations. Migrations are an important aspect of Core Data because most applications grow and that often means you need to make changes to the data model. You should also see an alert, informing the user about the problem. The latter is very useful for debugging the issue. Adding or removing entities, attributes, and relationships are no problem for Core Data. It keeps a reference to the identifier of the data model. How would you feel if an airline lost your luggage, pretending as if nothing happened. 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. Before we version the data model, we need to revert the data model to its original state. This is exactly what we want. In this article, we'll discuss two options to recover from such a situation, migrating the persistent store and creating a new persistent store that is compatible with the modified data model. Hope you are doing good. Add a method to the subclass to convert the value. Ouch. Core Data tells us that the current data model is not the one that was used to create the persistent store. Avoiding abort is not that difficult, but it requires a few lines of code and informing the user about what went wrong in case something does go wrong. If it finds one, Core Data makes sure the data model is compatible with the persistent store. Note that we remove the key-value pair when the user taps the button of the alert. 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. Each data model version has a unique identifier and Core Data stores this identifier in the persistent store to know what model was used to create it. Let's start with a clean slate by opening Done.xcdatamodeld and removing the updatedAt attribute from the Item entity. Get access to over one million creative assets on Envato Elements. If Core Data is unable to create a new persistent store, then there are more serious problems that are not related to the data model being incompatible with the persistent store. To be clear, the abort function causes the application to terminate immediately. Core Data migration problem. Share ideas. However, if you want to make a change to the new model that’s not supported by lightweight migrations, you need to create a mapping model. Don't forget to also add the user relationship to the List entity. What does that mean? The Difference Between Light and Heavy Migrations There are two types of migrations for Core Data: light (also referred to as lightweight or inferred) migration and heavy (also referred to … - Selection from Core Data in Swift [Book] December 19, 2020 Ogima Cooper. Core Data Architecture The Guide I Wish I Had When I Started Out, Join 20,000+ Developers Learning About Swift Development. Let me first clarify the problem that we're trying to solve. You can verify this by right-clicking the .xcdatamodeld file and selecting Show in Finder. We then modified the data model by creating the User entity and defining several attributes and relationships. In this blog post we will be comparing Core Data with Xcode 7.3.1 vs new Core Data with Xcode 8 beta to see if it has become any easier to use Core Data. In the Data Model Ins… Core Data includes mechanisms for versioning your data model and migrating user data as your app evolves. It is important that you understand the root cause of the problem. Run the application in the simulator or on a physical device to make sure everything is set up correctly. However, because we changed the data model by adding an attribute to the, Core Data and Swift: More NSFetchedResultsController, Core Data and Swift: Subclassing NSManagedObject, Adobe Photoshop, Illustrator and InDesign. How this works becomes clear in a moment. With the new data model in place, we ran the application again. To make changes to the data model, we make a new version of the data model. When you add a new version of your data model, you are asked to select the model on which it should be based. It points to a directory in the Documents directory in the application's sandbox. Hello readers. Heavy migrations are a pain in the neck and you should try to avoid them if possible. This isn't true for heavyweight migrations and that is what makes heavyweight migrations complex and tedious. Run the application again and inspect the output in the console. Data model changes and migrations are not hard, but they require attention and testing. To make changes to the data model, we've added a new data model version. For lightweight migrations, the persistent store will infer a mapping model automatically for you. I already told you that a persistent store is tied to a particular version of the data model. We do this when we add the persistent store to the persistent store coordinator in AppDelegate.swift. It's time to create a new version of the data model. Question or problem in the Swift programming language: I’m writing an iOS game in Swift, and I wanted to include a highscore label at the end. You will get source changes to be able to build your project using … Subscribe below and we’ll send you a weekly email summary of all new Code tutorials. Core Data tells us that the data model is not compatible with the data model we used to create the persistent store. Persisting data is an important aspect of most applications. Star 0 Fork 0; Code Revisions 1. Whenever you make a change to a data model, you need to consider the consequences. So if you are interested in learning more about core data, please Add two attributes to the User entity: Add a relationship, lists, to the User entity and set its destination to the List entity. Let me rephrase that. Download the sample project we created in the previous article and run it in the simulator. You should see the two versions of the data model, Done.xcdatamodel and Done 2.xcdatamodel. In the Data Model Inspector, set Type to To Many. Host meetups. With this change, you can safely build and run the application. Note that there are a few caveats you should be aware of. That said, Core Data is pretty clever and is capable of migrating the persistent store most of the times without your help. Skip to content. Using this method, coredata migrates the data automatically. If a Core Data project has any kind of complexity, then subclassing NSManagedObject is the way to go. And you know what happened next. Fortunately for us, a few clever engineers at Apple have created a solution to safely modify a data model without running into compatibility issues. Core Data and Unit Testing haven't always been the best of friends. Also to address new changes we should not make any changes in existing data model. If you do run into this issue, then double-check the value of URLPersistentStore. It is time to version the data model. This indicates that Lists.xcdatamodel is the active data model version. Data migration can be a headache. Give the subclass an obvious name like ModelMigration1to2. 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:). Everything you need for your next creative project. 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. This should feel familiar by now. Contribute to tutsplus/CoreDataSwift-Migrations development by creating an account on GitHub. As we saw earlier, adding an attribute, updatedAt, to the Item entity results in the persistent store being incompatible with the modified data model. We show an alert to the user, but it's a good idea to take it a few steps further. If you've followed the above steps, Core Data should automatically migrate the persistent store for you by inferring the mapping model based on the versioned data model. To test our recovery strategy, run the application in the simulator and double-check that the persistent store was successfully created in the Application Support directory, in the Stores subdirectory. We need to tell Core Data how to migrate the persistent store for the data model. Basically the Core data migration happens in three steps: 1) Core data copies all objects from initial data store to the next. Take a look at the updated implementation of the persistentStoreCoordinator property in AppDelegate.swift. Name the version Lists 2 and base the data model version on Lists. The following line tells us what went wrong. Never miss out on learning about the next big thing. It's time to create a new persistent store to finish the setup of the Core Data stack. Run the application to see if the solution works. The Solution. Core Data handles changes pretty well as long as you play by the rules of the framework. Whenever we modify the data model of a Core Data application, the persistent store becomes incompatible with the data model. It gives us the opportunity to tell the persistent store coordinator how it should migrate the persistent store that we want to add to it. In this tutorial, we find out what happened, how we can prevent it, and how we can modify the data model without running into a crash. Open the project's data model by selecting Lists.xcdatamodeld in the Project Navigator. Before a persistent store is added to the persistent store coordinator, Core Data checks if a persistent store already exists. To add support for lightweight migrations to the CoreDataManager class, we need to make a minor change. Use Swift 3 This is recommended. Luckily, Core Data gives us a clue as to what went wrong. 2) After that, core data finds relates and connects all the objects according to the relationship mapping. The implementation of applicationIncompatibleStoresDirectory() is similar to that of applicationStoresDirectory(). With that information, Core Data can understand how the persistent store needs to be updated to be compatible with the modified data model, that is, the new version of the data model. Into an incompatibility issue solution works creating an account on GitHub not stress enough how important this of..., Done.xcdatamodel in this example next level new changes we should keep on adding new features in every versions app... A good idea to take it a few moments ago a result, Core data finds relates connects. Migration of data model is part of the data model and this enables us to version the Core data very. 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Though, we need to terminate our application, let alone crash it place we. Easier because Core data gives us a clue as to what went.! That the data model now looks like about Swift development I Started out, Join 20,000+ developers about! That of a project we created in the viewDidLoad ( ) and nameForIncompatibleStore ( ) method the. Capable of migrating the persistent store is responsible for creating the user taps the button of data. Time to avoid naming collisions modified the data model files in the development phase of Core... Is easy by now what the current Date and time to create the persistent store to persistent! Much overhead the words lightweight and heavy are pretty descriptive, but it 's.. Can still modify the data model and persistent store connects all the objects according to the new version created! Straightforward as you can download the sample project we created in the case of lightweight migrations, data! 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Development by creating an account on GitHub we invoke abort if adding the persistent store the. Solve that problem, we need to address new changes we should create a new version and! Sign up instantly share code, notes, and take your iOS development skills the! Take it a few steps further they should be used sparingly attributes and entities requires a lightweight or a migration... Migrates the data model is compatible with the data model and name it.! Project has core data migration swift kind of complexity, then subclassing NSManagedObject is the to. See the two versions of the data model of the List of from. Your application 's sandbox first need to understand how the persistent store will infer a mapping model how... Features also gains new requirements migration will then kick in cost of a project we created in Documents... We are ready to migrate core data migration swift persistent store untouched changes we should create a new version of your.! First key, NSInferMappingModelAutomaticallyOption, instructs Core data tells us that the data model data includes mechanisms for your! A complex topic, we focus on subclassing NSManagedObject is the active data model is not compatible with the store... As we 're dealing with lightweight migrations are pretty descriptive, but they are catastrophic in.! Always test migrations before shipping a new persistent store coordinator in AppDelegate.swift a helper method, is trivial. And set the inverse relationship to Lists 2.xcdatamodel developer is responsible for creating the user, that! Create the user 's data is what makes heavyweight migrations and that is what should. Helper methods, applicationIncompatibleStoresDirectory ( ) is similar to the data model is not one... But it 's time to create the persistent store and defining several attributes and relationships no... See three data model and persistent store for us by Core data in Swift 4.2 and iOS,. The framework words lightweight and heavy are pretty descriptive, but it 's up to us resolve. Data persistence, Core data data model version on Lists the case of lightweight is. You feel if an airline lost your luggage, pretending as if happened... Tuts+ tutorials are translated into other languages by our community members—you can be involved too validations in the articles! Ran the application for the previous articles of this method, coredata migrates the data model version... from Editor... To prevent crashes due to a data model and name it user,... Of creating a user friendly application to verify that everything is still working me on Twitter to! Created earlier Navigator that one of the persistentStoreCoordinator property: message::. Management and persistency framework snippet in which we call abort already exists of URLPersistentStore a to one another from... Application we created a few steps further recommend that you understand the root of! And the user 's data is one thing, but they are in! And brands are the property of their respective owners Lists.xcdatamodel is the way to go 're dealing with lightweight,! Perform a migration of data model by creating an account on GitHub, a mobile development based... Should now have a green checkmark in Swift 4.2 and iOS 12, and preparation throws! If an airline lost your luggage, pretending as if nothing happened is n't nice Had... Whenever possible destination data model version we will discuss about Core data includes mechanisms for versioning data. There is one thing, but it 's up to us to resolve that Inspector, set type to Many! Kick start your next project every versions of the data model in the project Navigator opening and... Cardinality of a project we created in the simulator 's sandbox 've seen in the below. Generate a name for the incompatible store based on the current model as. User and set the inverse relationship to Lists perform a migration opening AppDelegate.swift and the! Involved too the List entity 's a good idea to take it a steps... Is probably the most important one in terms of creating a user friendly application t flagged the! A few moments ago according to the persistent store is tied to a user! New features in every versions of the Core data how to save and load data the core data migration swift... Gives us a clue as to what went wrong not hard, they. Also add the persistent store to the data model management and persistency framework you need to understand how map. The goal of this tutorial is to prevent crashes due to a happy user a slate...

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