Core Data Interview Questions: Quick Guide

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Core Data is one of the most commonly discussed topics in iOS developer interviews. Whether you’re preparing for junior, mid-level, or senior roles, this guide covers all Core Data interview questions—from basics to advanced concepts and real-world scenarios.

#Basic Level Core Data Questions

1. What is Core Data?

Core Data is Apple’s framework for managing the model layer of your app. It supports:

Local data persistence
Object graph management
Change tracking
Undo/redo functionality

2. What are the main components of Core Data?

NSManagedObjectModel
NSManagedObjectContext
NSPersistentStoreCoordinator
NSPersistentContainer (introduced in iOS 10)

3. What is an `NSManagedObject`?

It’s a class representing a single object stored in Core Data.
It maps directly to an entity in your .xcdatamodeld.

4. How do you save data in Core Data?

Create an NSManagedObject.
Set its properties.
Call save() on the context:

try context.save()

5. How do you fetch data in Core Data?

Using NSFetchRequest, optionally with:

Predicates
SortDescriptors
Limits

#Intermediate Level Core Data Questions

6. What is an `NSPersistentContainer`?

A convenience wrapper that contains:

Model
Context
Store coordinator

It simplifies Core Data stack setup.

7. What is `NSManagedObjectContext` and why is it important?

It is a workspace/scratchpad where you:

Create objects
Modify objects
Track changes
Save or undo changes

8. What’s the difference between main context and background context?

Main context: Runs on main thread → use for UI-related tasks
Background context: Runs on background queue → use for heavy operations

9. What is a predicate in Core Data?

NSPredicate filters fetch results.
Example:

NSPredicate(format: "name == %@", "Alice")

10. What are relationships in Core Data?

Entities can have:

One-to-One
One-to-Many
Many-to-Many

Relationships also support delete rules.

#Advanced Level Core Data Questions

11. How is Core Data different from SQLite?

Core Data	SQLite
Object graph manager	Simple database
Supports faulting, undo, validation	Raw SQL
Manages relationships automatically	Manual joins
Uses SQLite internally (optional)	SQL only

Note: For Detailed Core Data vs Sqlite vs Realm comparison, check here.

12. What are merge policies?

Used to resolve conflicts when multiple contexts save changes.

Common merge policies:

mergeByPropertyObjectTrump
mergeByPropertyStoreTrump
overwrite
rollback

13. How do you handle concurrency in Core Data?

Use background contexts
Use perform or performAndWait
Avoid passing NSManagedObject instances across threads
Use object IDs instead

14. What types of persistent stores does Core Data support?

SQLite (default)
Binary
In-memory

15. What is faulting in Core Data?

Faulting is a lazy-loading mechanism:

Objects are placeholders until their properties are accessed
Saves memory and improves performance

16. What is Core Data migration?

When a data model changes, Core Data must migrate old data.

Types:

Lightweight Migration: Automatically handles simple changes
Heavy/Custom Migration: Requires mapping models

17. What is `NSFetchedResultsController`?

A controller that monitors Core Data objects and updates UI components—mostly used with UITableView and UICollectionView.

#Practical / Scenario-Based Core Data Questions

18. How to efficiently insert a large number of records?

Use background context
Disable undo manager
Save in batches (e.g., every 100 inserts)

19. What are some Core Data performance best practices?

Use faulting
Avoid large fetches
Use batch updates / batch deletes
Use indexing for frequently queried attributes

20. How do you test Core Data logic?

Use an in-memory store for unit tests
Mock NSManagedObjectContext
Isolate business logic