Cannot create nsarray from object relationship fault for

Core Data Programming Guide: Faulting and Uniquing

First, given an array of faults, how to retrieve meta information public static void batchFetchObjects(NSArray someObjects) { if ((someObjects! You usually don't run into a situation where you want to create faults instead of just fetching objects from [When I had a semantic relationship, but couldn't actually model the. Relationship Definitions in the Model Relationship Fault cannot be fulfilled Managed object Cannot create new objects with array controller NSArrayController or NSTreeController object Core Data. To make faulting work, Core Data does a bit of magic under the hood by 2: Relationship 'items' fault on managed object (0xe5d0b0) fault that cannot be fulfilled.

You started with a strong reference to a managed object from another object in your application. You deleted the managed object through the managed object context. You saved changes on the object context.

At this point, the deleted object has been turned into a fault. Core Data will try to realize the faulted managed object but will fail to do so because the object has been deleted from the store.

That is, there is no longer an object with the same global ID in the store. You deleted an object from a managed object context. The deletion failed to break all relationships from other objects to the deleted object.

At this point, if you try to fire the fault of a relationship from another object to the deleted object, it may fail, depending on the configuration of the relationship, which affects how the relationship is stored. The delete rules for relationships affect relationships only from the source object to other objects including inverses. Without potentially fetching large numbers of objects, possibly without reason, there is no way for Core Data to efficiently clean up the relationships to the object.

Keep in mind that a Core Data object graph is directional. That is, a relationship has a source and a destination. Following a source to a destination does not necessarily mean that there is an inverse relationship. So, in that sense, you need to ensure that you are properly maintaining the object graph across deletes.

Core Data uses inverse relationships to maintain referential integrity within the data model. If no inverse relationship exists and an object is deleted, you will be required to clean up that relationship manually. In practice, a well-designed object graph does not require much manual post-deletion clean-up. Most object graphs have entry points that in effect act as a root node for navigating the graph, and most insertion and deletion events are rooted at those nodes just like fetches.

This means that delete rules take care of most of the work for you. Similarly, because smart groups and other loosely coupled relationships are generally best implemented with fetched properties, various ancillary collections of entry points into the object graph generally do not need to be maintained across deletes, because fetched relationships have no notion of permanence when it comes to objects found through the fetched relationship.

Managed object invalidated Problem: You see an exception that looks similar to this example: Either you have removed the store for the fault you are attempting to fire, or the managed object's context has been sent a reset. If you add the store again, you can try to fetch the object again.

Class is not key-value coding-compliant Problem: You see an exception that looks similar to the following example. Either you used an incorrect key, or you initialized your managed object with init instead of initWithEntity: Use a valid key check the spelling and case carefully—also review the rules for key-value coding compliance in Key-Value Coding Programming Guide. Entity class does not respond to invocations of custom methods Problem: You define an entity that uses a custom subclass of NSManagedObject, then in code you create an instance of the entity and invoke a custom method, as illustrated in this code fragment: In the model, you misspelled the name of the custom class for the entity.

Ensure that the spelling of the custom class name in the model matches the spelling of the custom class you implement. Custom accessor methods are not invoked, and key dependencies are not obeyed Problem: You define a custom subclass of NSManagedObject for a particular entity and implement custom accessors methods and perhaps dependent keys.

At runtime, the accessor methods are not called, and the dependent key is not updated. In the model, you did not specify the custom class for the entity.

Firebase Database Querying 101 - The Firebase Database For SQL Developers #3

Ensure that the model specifies the custom class name for the entity rather than NSManagedObject. You create a sort descriptor that uses a comparison method defined by NSStringsuch as the following: You then either use this descriptor with a fetch request or as one of an array controller's sort descriptors. At runtime, you see an error message that looks similar to the following: Exactly how a fetch request is executed depends on the store—see Fetching Objects.

If you are executing the fetch directly, do not use Cocoa-based sort operators—instead, sort the returned array in memory. If you are using an array controller, you may need to subclass NSArrayControllerso that it will not pass the sort descriptors to the database but will instead do the sorting after your data has been fetched. Problems with Saving Cannot save documents because entity is null Problem: You have a Core Data document-based application that is unable to save.

When you try to save the document you get an exception: Exception raised during posting of notification. Cannot perform operation since entity with name 'Wxyz' cannot be found Cause: In short, you have a controller in entity mode with an invalid entity name.

Select in turn each of your controllers in Interface Builder, and press Command-1 to show the inspector. For each controller, ensure you have a valid entity name in the Entity name field at the top of the inspector. You add an object to a context. When you try to save the document you get an error that looks like this: Basically, it's checking to see if any other code thread, process, or just a different managed object context changed this object without your knowledge.

Core Data does not do this check on newly inserted objects because they could not have existed in any other scope. They haven't been written to the database yet.

You may have forced a newly inserted object to lose its inserted status and then changed or deleted it. You may have passed an inserted object to another managed object context. There are a number of possible remedies, depending on the root cause: Do not pass an inserted not yet saved object to another context. Only objects that have been saved can be passed between contexts. Do not invoke refreshObject: Do not make a relationship to an object that you never insert into the context.

Ensure that you use the designated initializer for instances of NSManagedObject. Debugging Fetching Use the user default com.

Core Data Programming Guide: Troubleshooting Core Data

Note that user default names are case sensitive. A managed object fault is an instance of the appropriate class, but its persistent variables are not yet initialized. A relationship fault is a subclass of the collection class that represents the relationship. Faulting allows Core Data to put boundaries on the object graph.

Because a fault is not realized, a managed object fault consumes less memory, and managed objects related to a fault are not required to be represented in memory at all. To illustrate, consider an application that allows a user to fetch and edit details about a single employee. The employee has a relationship to a manager and to a department, and these objects in turn have other relationships. If you retrieve just a single Employee object from a persistent store, its manager, department, and reports relationships are initially represented by faults.

Figure A department represented by a fault Although the fault is an instance of the Department class, it has not yet been realized—none of its persistent instance variables have yet been set. If it were a requirement that the object graph be complete, then to edit a single attribute of a single employee, it would ultimately be necessary to create objects to represent the whole corporate structure. Firing Faults Fault handling is transparent—you do not have to execute a fetch to realize a fault.

If at some stage a persistent property of a fault object is accessed, Core Data automatically retrieves the data for the object and initializes the object.

WebObjects/EOF/Using EOF/Batch Fetching

This process is commonly referred to as firing the fault. If you access a property on the Department object — its name, for example — the fault fires and Core Data executes a fetch for you to retrieve all of the object's attributes. See NSManagedObject for a list of methods that do not cause faults to fire. Core Data automatically fires faults when a persistent property such as firstName of a fault is accessed. However, firing faults individually can be inefficient, and there are better strategies for getting data from the persistent store see Decreasing Fault Overhead.

When a fault is fired, Core Data does not go back to the store if the data is available in its cache. With a cache hit, converting a fault into a realized managed object is very fast—it is basically the same as normal instantiation of a managed object.

If the data is not available in the cache, Core Data automatically executes a fetch for the fault object; this results in a round trip to the persistent store to fetch the data, and again the data is cached in memory. Whether or not an object is a fault simply means whether or not a given managed object has all its persistent attributes populated and is ready to use. If you need to determine whether an object is a fault, call its isFault method without firing the fault without accessing any relationships or attributes.

If isFault returns NOfalse, then the data must be in memory and therefore the object is not a fault. However, if isFault returns YEStrue, it does not imply that the data is not in memory. The data may be in memory, or it may not, depending on many factors influencing caching. You are strongly discouraged from overriding description in this way. There is no way to load individual attributes of a managed object on an as-needed basis and avoid realizing retrieving all property values of the entire object.

Turning Objects into Faults Turning a realized object into a fault can be useful in pruning the object graph, as well as ensuring that property values are current. Turning a managed object into a fault releases unnecessary memory and sets its in-memory property values to nil. You can turn a realized object into a fault with the refreshObject: