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name: ios-coredata-pattern version: 0.1.0 author: cmtzco description: iOS Core Data persistence and data modeling guide. When to use: when implementing data storage in iOS apps, creating new Core Data entities, setting up persistent storage, working with SQLite databases, or managing data relationships. What problems it solves: provides robust data persistence with automatic schema migrations, manages complex object relationships, enables efficient querying and filtering, and handles background threading for data operations.

iOS Core Data Pattern

Overview

Core Data is Apple's framework for managing the model layer of an iOS application. This skill guides you through setting up Core Data stacks, defining entities and relationships, creating NSManagedObject subclasses, and performing common CRUD operations.

Identified Patterns

The following patterns were identified in this codebase that this skill addresses:

Pattern 1: Persistent Container Setup

• Location: DadBrain/DadBrain/Models/PersistenceController.swift
• Description: NSPersistentContainer initialization with preview environment support
• Frequency: 1 shared controller used throughout app

Pattern 2: Entity Extensions

• Location: DadBrain/DadBrain/Models/Memory+CoreDataClass.swift
• Description: NSManagedObject extensions with computed properties and convenience methods
• Frequency: 2 entity extensions (Memory, Tag)

Pattern 3: Data Model Definition

• Location: DadBrain.xcdatamodeld
• Description: Core Data model with entities, attributes, and relationships
• Frequency: 3 models defined (Memory, Tag, PersistenceController)

TODO: Implementation

This skeleton skill needs Phase 2 refinement. Areas to develop:

Workflow Instructions

1. Create or modify .xcdatamodeld file in Xcode
2. Define entities, attributes, and relationships
3. Generate NSManagedObject subclasses
4. Set up NSPersistentContainer
5. Create convenience methods and computed properties

Best Practices

• Background context vs main context usage
• Relationship management (delete rules)
• Lightweight migration strategies
• Performance optimization (batching, fetching)

Common Pitfalls

• Not performing saves on proper thread
• Forgetting to handle migration when model changes
• Memory leaks from retaining managed objects
• Over-fetching or missing fetch predicates

Suggested Resources

Based on codebase analysis, consider adding:

Scripts (scripts/)

• core-data-migration-generator.swift - Generates migration mapping models
• entity-extension-generator.swift - Creates boilerplate NSManagedObject extensions

References (references/)

• core-data-best-practices.md - Apple's Core Data programming guide
• migration-strategies.md - Handling data model changes
• fetch-optimization.md - Performance tips for queries

Assets (assets/)

• entity-templates/ - Common entity patterns (timestamped, soft-delete, etc.)
• migration-templates/ - Migration code templates

Evidence from Codebase

Refinement Priority

Score: 6.8/10 Priority: Medium

Refinement Tasks

1. Research Core Data lifecycle and context management
2. Create entity-extension-generator script
3. Document relationship types and delete rules
4. Add examples for common query patterns
5. Create migration guide for model changes

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Skeleton generated by ContextHarness /baseline Run Phase 2 skill refinement to complete implementation