Merge pull request 'docs: add Claude development guidelines for database migrations' (#4) from add-claude-migration-guide into main

Reviewed-on: #4

CLAUDE.md

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+# Claude Development Guidelines
+
+## Database Migrations
+
+**⚠️ IMPORTANT: When making changes to database models or schema, you MUST create migration files.**
+
+### When to Create Migrations
+
+**ALWAYS create a migration when:**
+- Adding new columns to existing tables
+- Creating new tables
+- Modifying column types or constraints
+- Adding or removing indexes
+- Changing default values
+- Adding foreign keys or relationships
+
+**Examples that require migrations:**
+```python
+# Adding a new field to PetPicture model
+class PetPicture:
+    # ... existing fields ...
+    tags = models.TextField()  # ❌ Requires migration!
+```
+
+```python
+# Changing database schema in init_db()
+def init_db():
+    db.execute("""
+        CREATE TABLE users (  -- ❌ New table requires migration!
+            id INTEGER PRIMARY KEY,
+            username TEXT NOT NULL
+        )
+    """)
+```
+
+### How to Create Migrations
+
+1. **Navigate to migrations directory:**
+   ```bash
+   cd migrations/
+   ```
+
+2. **Create new migration file:**
+   ```bash
+   # Use next sequential number (002, 003, etc.)
+   touch XXX_descriptive_name.py
+   ```
+
+3. **Use the migration template:**
+   ```python
+   #!/usr/bin/env python3
+   """
+   Migration XXX: Brief description of changes
+   Date: YYYY-MM-DD
+   Description: Detailed explanation of what this migration does
+   """
+   
+   import sqlite3
+   import sys
+   from datetime import datetime
+   
+   def check_column_exists(cursor, table_name, column_name):
+       """Check if a column exists in a table"""
+       cursor.execute(f"PRAGMA table_info({table_name})")
+       columns = [column[1] for column in cursor.fetchall()]
+       return column_name in columns
+   
+   def migrate_up(cursor):
+       """Apply the migration"""
+       # Check if already applied
+       if check_column_exists(cursor, 'pet_pictures', 'new_column'):
+           print("Migration already applied, skipping...")
+           return False
+           
+       # Apply the migration
+       print("Adding new_column to pet_pictures table...")
+       cursor.execute("ALTER TABLE pet_pictures ADD COLUMN new_column TEXT")
+       return True
+   
+   def migrate_down(cursor):
+       """Rollback the migration (optional)"""
+       print("Rollback not implemented for SQLite column drops")
+       return False
+   
+   def main():
+       """Run migration standalone"""
+       # Standard migration execution code
+       pass
+   
+   if __name__ == "__main__":
+       sys.exit(main())
+   ```
+
+4. **Test the migration:**
+   ```bash
+   # Test individual migration
+   python migrations/XXX_descriptive_name.py
+   
+   # Or run all pending migrations
+   python migrations/migrate.py
+   ```
+
+5. **Commit the migration file:**
+   ```bash
+   git add migrations/XXX_descriptive_name.py
+   git commit -m "feat: add migration for [description]"
+   ```
+
+### Migration Naming Convention
+
+- **Sequential numbering**: `001_`, `002_`, `003_`, etc.
+- **Descriptive names**: Explain what the migration does
+- **Examples**:
+  - `002_add_user_table.py`
+  - `003_add_tags_column_to_pictures.py`
+  - `004_create_comments_table.py`
+
+### DO NOT Modify Database Schema Without Migrations
+
+**❌ NEVER do this:**
+```python
+# Directly modifying init_db() or model schema
+def init_db():
+    db.execute("""
+        CREATE TABLE pet_pictures (
+            id INTEGER PRIMARY KEY,
+            filename TEXT NOT NULL,
+            new_field TEXT  -- ❌ Added without migration!
+        )
+    """)
+```
+
+**✅ ALWAYS do this:**
+1. Create migration file first
+2. Run migration to update schema
+3. Then update model code if needed
+
+### Model Changes Workflow
+
+1. **Identify needed schema change**
+2. **Create migration file**
+3. **Test migration locally**
+4. **Update model/application code** (if needed)
+5. **Test full application**
+6. **Commit migration + code changes together**
+
+### Migration Best Practices
+
+- **One logical change per migration**
+- **Make migrations idempotent** (safe to run multiple times)
+- **Test on development data first**
+- **Include rollback logic when possible**
+- **Document breaking changes clearly**
+- **Never edit applied migrations**
+
+### Integration Points
+
+**Development:**
+```bash
+# Apply migrations before starting app
+python migrations/migrate.py && python main.py
+```
+
+**Docker:**
+```bash
+# Migrations run automatically via docker-compose
+docker compose --profile migrate up migrate
+```
+
+**Production Deployment:**
+```bash
+# Run migrations as part of deployment
+python migrations/migrate.py
+systemctl restart pet-picture-queue
+```
+
+---
+
+## Database Schema Reference
+
+**Current Schema (after migrations):**
+
+### `pet_pictures` table:
+- `id` - INTEGER PRIMARY KEY AUTOINCREMENT
+- `filename` - TEXT NOT NULL
+- `subscriber_name` - TEXT NOT NULL  
+- `description` - TEXT NULL (added via migration 001)
+- `uploaded_at` - TIMESTAMP NOT NULL
+- `posted` - BOOLEAN DEFAULT 0
+- `likes` - INTEGER DEFAULT 0
+
+### `migrations` table (auto-created):
+- `id` - INTEGER PRIMARY KEY AUTOINCREMENT
+- `migration_name` - TEXT NOT NULL UNIQUE
+- `applied_at` - TIMESTAMP NOT NULL
+
+---
+
+**Remember: Schema changes without migrations will cause deployment issues and data inconsistencies!**
+
+Always follow the migration workflow for database changes.