Core Data Relationships – Hacker Noon
if your Review shall be a relationship in your coreDataModel, please use instead of NSMutableArray the NSSet and connect it with the Restaurant Entity. Core Data from Scratch: Managed Objects and Fetch Requests In the above example, we only set the record's street and city attributes. One-To-One and One-To-Many Relationships .. NSPredicate *predicate = [ NSPredicate predicateWithFormat: @"%K CONTAINS[c] %@ AND %K < 30", @"first". Explains how to manage objects using the Core Data framework. In an object model relationship, you have a source entity (for example, A relationship specifies the entity, or the parent entity, of the objects at the destination. is akin to declaring an instance variable in a standard Objective-C class.
Objects are linked to each other by one object either owning or containing another object or holding a reference to another object to which it sends messages. This web of objects is called an object graph. An array object that contains a single string object represents a small, simple object graph.
A group of objects containing an application object, with references to the windows, menus and their views, and other supporting objects, may represent a large, complex object graph.
This is what the data model should look like in the data model graph. A relationship specifies the entity, or the parent entity, of the objects at the destination. This means that we need to create a relationship that links a book to a library.
Getting Started with Core Data Tutorial
We can conclude below points: The relationship is to-one relationship. A book can belong to one library only.
The single arrow is pointing from book entity to library entity. It means that the library the book belongs to does not know that the library belongs to this book. How to make a relationship system where library knows what books it contains.
We have following relationship: Switch to the data model graph to see what that looks like.
Core Data Programming Guide: Creating Managed Object Relationships
Switch back to graph to see changes. This is what the data model graph looks like after the changes. Very important note The recommended approach is to model relationships in both directions and specify the inverse relationships appropriately.
Core Data uses this information to ensure the consistency of the object graph if a change is made. You might get this warning if you set no inverse relationship in Xcode: Add relationship from Address to Person Destination like this: And finally it should look like this: Create a new project in Xcode.
Now click on CoreDataRelationships.
Swift – Core Data – Part 1 | Relationships | Delete Rules
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. For example, if you delete a department, fire all the employees in that department at the same time.
ios - Core Data : Insertion into One to Many Relationship - Stack Overflow
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. It should be clear that the first three of these rules are useful in different circumstances. For any given relationship, it is up to you to choose which is most appropriate, depending on the business logic.
It is less obvious why the No Action rule might be of use, because if you use it, it is possible to leave the object graph in an inconsistent state employees having a relationship to a deleted department. If you use the No Action rule, it is up to you to ensure that the consistency of the object graph is maintained.
- One-to-Many and Many-to-Many Core Data Relationships
- Core Data Relationships
You are responsible for setting any inverse relationship to a meaningful value. This may be of benefit in a situation where you have a to-many relationship and there may be a large number of objects at the destination. Manipulating Relationships and Object Graph Integrity When you modify an object graph, it is important to maintain referential integrity. Core Data makes it easy for you to alter relationships between managed objects without causing referential integrity errors.
Much of this behavior derives from the relationship descriptions specified in the managed object model. When you need to change a relationship, Core Data takes care of the object graph consistency maintenance for you, so you need to change only one end of a relationship.
This feature applies to to-one, to-many, and many-to-many relationships. Consider the following examples. If a new employee is assigned to a particular manager, it is important that the manager be made aware of this responsibility.