Core data relationship fault on managed object format

Core Data on iOS 10, a brief overview with an Example

core data relationship fault on managed object format

Core Data is Apple's object graph management and persistency framework for iOS, . When you start with an empty Xcode template for an iOS or macOS app, you . Often, they can be avoided by traversing relationships, something which .. as long as a managed object with this object ID exists, whether it's a fault or not. Oct 30, Faults are an essential component of Core Data. Even though the term I've created a simple sample application to work with. Download the Xcode 2: Relationship 'items' fault on managed object (0xe5d0b0)

Remove the print statement of the if clause and replace it with the following to better understand how faulting works. This means that Core Data needs to fire or resolve the fault.

Core Data fetches the missing data from the persistent store to fill in the gaps. Note that we only see a fault if the list record is fetched from the persistent store. A newly created managed object doesn't have any faults because it hasn't been fetched from a persistent store.

Take a closer look at the last print statement. Have you noticed that the items relationship is also a fault. The values of the name and createdAt attributes are resolved, but the items relationship isn't. This is another Core Data optimization. Faulting is something you need to become familiar with if you plan to use Core Data.

Reading and Updating Managed Objects With Core Data

Most of the time, it's something you don't need to worry about. Updating Records How to Update an Attribute of a Managed Object The above output shows us that the list record we fetched from the persistent store doesn't have a name or creation date.

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We can fix that by updating the list record and saving the changes. Run the application to update the list record. This is what you see in the console if the record doesn't have a name or creation date. It should look something like this: The documentation tells us that the return type of value forKey: This isn't ideal and it is something we fix later in this series.

What's important is that we have updated the list record and pushed the updates to the persistent store. How to Update a Relationship of a Managed Object Working with relationships is similar to working with attributes.

There are a few differences you need to be aware of. Setting or updating a to-one relationship is identical to setting or updating an attribute. Working with to-many and many-to-many relationships is different. The items relationship of the list record, for example, is a set NSSet of item records. Most developers new to Core Data expect an array or an ordered set. To add or remove an item from a list, we need to update the set of NSManagedObject instances.

Let me show you how that works. 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. If you inspect the output in the console, you can see that the set of item records is unordered.

As Apple states, it is not a database, but instead a persistence framework that commonly uses SQLite to store and retrieve structured data. For programmers, it operates purely on the object level without having to worry about the details of storage and retrieval.

Relationships - Beginning Core Data -

At first the Core Data framework may seem difficult to understand. 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.

Core Data Programming Guide: Faulting and Uniquing

The Managed Object Model, describes the schema that you will be using in your application. In Xcode, by selecting this. 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.

core data relationship fault on managed object format

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.

After you press enter, the Class name, below the section Entity, will also be updated with the desired name. In this case, the editor will be expecting you to change the name and select a valid type. After you create this new attribute it should look like the picture below. That is one of the responsabilities of Core Data and it is the framework that will create the logic for your entity internally.

After this we want to create a relationship between these two entities, where a task can have multiple notes. You will notice that a warning appears.

core data relationship fault on managed object format

This is not strictly required, but setting the inverse relationship will help Core Data ensure the consistency of the object graph when a change is made.