Note that a green checkmark is added to Lists. You will notice that a warning appears. Add an entity to the data model and name it User. Data model changes and migrations are not hard, but they require attention and testing. You can download the final project from this tutorial here. Image Attachments Now the data is migrated, you need to update the UI to allow image attachments to new notes. 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 older version is there to support migration. Core Data disables destination model validations during the data copy. With the new data model in place, we ran the application again. How to Update a Relationship of a Managed Object Working with relationships is similar to working with attributes. That said, Core Data is pretty clever and is capable of migrating the persistent store most of the times without your help.
If you don't invest time architecting the data model, chances are you run into problems that could have been avoided. The next logical step is to add more to the model; however, this requires a number of preliminary steps in order to prevent crashes caused by these changes. What do you do then? The Managed Object Model, describes the schema that you will be using in your application. Setting or updating a to-one relationship is identical to setting or updating an attribute. Update Grocery Dude as follows to revert to the original model: Add a title there is default text in the note body to make the process faster and tap Create to save the new note to the data store. Click the triangle to show the list of data model versions. In the example, we create an item record, set its attributes, set its list relationship, and add it to the items relationship of the list record. Run the application again. That's not what we have in mind, though. In the new model, changes must fit an obvious migration pattern, such as: Remember that the inverse relationship of the lists relationship is automatically set for us by Core Data. Going back to code, add the following instance and method into the ViewController. As such, this scenario is unacceptable for any application already available on the App Store. The documentation tells us that the return type of value forKey: This chapter covers the basics of setting up your data model and then adding and fetching records. Keep It Lightweight Whenever you make a change to a data model, you need to consider the consequences. When you click it, you will see a tool that allows you to configure entities which represents data models. Core Data handles changes pretty well as long as you play by the rules of the framework. To make changes to the data model, we make a new version of the data model. To get past it, you can just delete the application and run it again. It is time to version the data model. Designing a simple User Interface Since the main goal of this article is not related to how we design user interfaces, I will give you a quick setup to support this article. The full chapter in the Core Data by Tutorials book follows up this Core Data migrations tutorial with a series of more complex migrations.
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