Ios core data relationship inverse matrix

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

ios core data relationship inverse matrix

Apple recommends that you always add an inverse value, so never leave this This is one of the advantages of Core Data before others. The first to-many relationship goes from the first entity (the You then set each to be the inverse of the other. This post is part of a series called Core Data from Scratch. . If a relationship has an inverse relationship, then Core Data takes care of this automatically. To remedy this, remove the application from your device or iOS.

GitHub Demonstration project for Core Data Issues I decided to create a demonstration project to provide test cases for all the issues that I was encountering, as a means of documenting them for reproducibility when I filed a bug using the Apple Bug Reporter. What are are the main issues? My goal was to release all memory held by Core Data after I did a save.

I had no need to keep any of the managed objects in memory after an import for my particular use case. The main issues I found were: Faulting all objects with refreshObject did not release all memory.

ios core data relationship inverse matrix

Performing a context reset did not release all memory. In the case of an inverse relationship this had no effect. Then add to your ViewController. To fetch objects from the database the best aproach, and the solution Apple wants us to use, is the NSFetchedResultsController. Fetched results controllers can fetch efficiently records from a predicate and a sort order.

It can also monitor changes to objects in the associated managed object context, and report changes in the result sets to its delegate.

ios core data relationship inverse matrix

After creating it, we will use a var of the same type to access this fetched results controller instance. With this, we will only initialize the controller at the moment that var will be used, similiar to a lazy aproach.

objective c - Does every Core Data Relationship have to have an Inverse? - Stack Overflow

The benefits of this are that we guarantee the instance will be initialized at the moment it will be used. And whenever a change occurs, the fetched results controller will call the method controllerDidChangeContent: Go ahead, include the method and call the reload data from the table view variable to refresh his data.

First the Table View will ask how many sections our data contains. Then the number of rows for each section. And the updated cell for each object.

ios core data relationship inverse matrix

At this point, if you run the application, you will only see the user interface that we have created before. For editing and deleting, we will implement the optional delegate method the Table View has to offer.

Core Data Relationships

Include the following code into the ViewController. Many thanks for reading! The final project can be found on the following link: MyTasks - A simple Core Data examplegithub.

ios core data relationship inverse matrix

Data persistence is always important for any application. Relationship Delete Rules A relationship's delete rule specifies what should happen if an attempt is made to delete the source object. Note the phrasing if an attempt is made. If a relationship's delete rule is set to Deny, it is possible that the source object will not be deleted. Consider again a department's employees relationship and the effect of the different delete rules.

Deny If there is at least one object at the relationship destination employeesdo not delete the source object department. For example, if you want to remove a department, you must ensure that all the employees in that department are first transferred elsewhere; otherwise, the department cannot be deleted.

Nullify Remove the relationship between the objects, but do not delete either object. This only makes sense if the department relationship for an employee is optional, or if you ensure that you set a new department for each of the employees before the next save operation. Cascade Delete the objects at the destination of the relationship when you delete the source.

  • One-to-Many and Many-to-Many Core Data Relationships
  • Core Data issues with memory allocation

For example, if you delete a department, fire all the employees in that department at the same time. No Action Do nothing to the object at the destination of the relationship. For example, if you delete a department, leave all the employees as they are, even if they still believe they belong to that department.