Core Data Fundamentals - CheatSheet (Simple)

README.md

Core Data Fundamentals - CheatSheet (Simple)

Here, I will save basic coredata information for anyone/me would like a quick refresh for these fundamentals from time to time.

What is Core Data

• Core Data is not a database, but instead it manages an Object Graph.

Multithreading

• NSManagedObject and NSManagedObjectContext in Core Data are not thread-safe.

• Core Data avoids data race issues by operating on NSManagedObject instances and NSManagedObjectContext instances in a serial queue.
  This is why we need to place the operation code within the closures of perform or performAndWait.

• Developers should perform operations on the main thread queue for the view context and the managed object instances registered within it. Similarly, we should perform operations on the serial queue created by the private context for private contexts and the managed objects registered within them.

Several Tips on Core Data Concurrency Programming

• Enable Core Data Concurrency Debugging Parameters
  To void issues like .......... to be continued

Misc

• ModelContext of SwiftUI is like a wrapped version of NSManagedObjectContext

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References:

• Core Data Fundamentals - Exploring the Core Data Stack
  https://cocoacasts.com/exploring-the-core-data-stack

• Concurrent Programming in SwiftData https://betterprogramming.pub/concurrent-programming-in-swiftdata-c9bf021a4c2d

Overview of CoreData Stack

• These are the core classes of CoreData: Management Object Model, Managed Object Context, Persistent Store Coordinator
  

• Here is how these classes are related to one way to another:
  

Managed Object Model

• It is instance of NSManagedObjectModel class.
• It represents the data model of the application.
  
• and it is connected directly to Data Model object.
  

Data Model

• It is represented by a file in the application bundle.

• It contains the data schema of the application.

• It is nothing more than a collection of entities.
  

• An entity have a collection of attributes, and relationships.

Managed Object Context

• It is an instance of NSManagedObjectContext class.

• An app can have one or more managed object context.

• It is the object you interact with most.

• It Creates, Reads, Updates, Deletes Managed Objects.

• Each managed object context manages a collection of Managed Objects.
  

• It receives the Managed Object through a Persistent Store Coordinator
  

Persistent Store Coordinator

• It is an instance of NSPersistentStoreCoordinator class.
• It is possible to have one or more of it in a single application.
• Most applications have only one instance of it.
• It is connected to one or more Persistent Stores.
  

What is a Persistent Store

• Core Data supports 3 types: SQLite, Binary, In-Memory.

How Does Core Data Works

• The heart of Core Data is the Persistent Store Coordinator.

• Persistent Store Coordinator is instantiated first when core data is created.

• Persistent Store Coordinator needs Managed Object Model instance to know what data schema for the application look like.

• After that, the Managed Object Context is initialized.

• Now the core data is setup, and application is ready to interact the application Persistent Store through the Managed Object Context.

• When the changes made to Managed Context Object or saved, it pushes them to the Persistent Store Coordinator which send the changes to the corresponding Persistent Store.

• When you have multiple Persistent Store, the Persistent Store Coordinator figures out which one is needed to save the changes.

NSPersistentContainer Class

• It encapsulates the details of setting and managing a core data stack.