ERPNext Custom App - Implementation
This skill helps you determine HOW to build and structure Frappe/ERPNext custom apps. For exact syntax, see erpnext-syntax-customapp.
Version: v14/v15/v16 compatible (differences noted)
Main Decision: What Are You Building?
┌─────────────────────────────────────────────────────────────────────────┐
│ WHAT DO YOU WANT TO CREATE? │
├─────────────────────────────────────────────────────────────────────────┤
│ │
│ ► Completely new Frappe/ERPNext app? │
│ └─► See: NEW APP WORKFLOW │
│ │
│ ► Extend existing ERPNext functionality? │
│ └─► See: EXTENSION DECISION │
│ │
│ ► Migrate data between fields/DocTypes? │
│ └─► See: PATCH vs FIXTURE DECISION │
│ │
│ ► Export configuration for deployment? │
│ └─► See: FIXTURE WORKFLOW │
│ │
│ ► Update existing app to newer Frappe version? │
│ └─► See: VERSION UPGRADE WORKFLOW │
│ │
└─────────────────────────────────────────────────────────────────────────┘Decision 1: Do You Need a Custom App?
┌─────────────────────────────────────────────────────────────────────────┐
│ DO YOU ACTUALLY NEED A CUSTOM APP? │
├─────────────────────────────────────────────────────────────────────────┤
│ │
│ What changes do you need? │
│ │
│ ► Add fields to existing DocType? │
│ └─► NO APP NEEDED: Use Custom Field + Property Setter │
│ (Can be exported as fixtures from ANY app) │
│ │
│ ► Simple automation/validation? │
│ └─► NO APP NEEDED: Server Script or Client Script │
│ (Stored in database, no deployment needed) │
│ │
│ ► Complex business logic, new DocTypes, or Python code? │
│ └─► YES, CREATE APP: You need controllers, models, and deployment │
│ │
│ ► Integration with external system? │
│ └─► USUALLY YES: APIs need whitelisted methods, scheduled sync │
│ │
│ ► Custom reports with complex queries? │
│ └─► DEPENDS: Script Report (no app) vs Query Report (app optional) │
│ │
└─────────────────────────────────────────────────────────────────────────┘Rule: Start with the SIMPLEST solution. Server Scripts + Custom Fields solve 70% of customization needs without a custom app.
Decision 2: Extension Strategy
┌─────────────────────────────────────────────────────────────────────────┐
│ HOW TO EXTEND ERPNext? │
├─────────────────────────────────────────────────────────────────────────┤
│ │
│ ► Add fields to existing DocType (e.g., Sales Invoice)? │
│ └─► Custom Field (via UI or fixtures) │
│ └─► Property Setter for behavior changes │
│ │
│ ► Modify DocType behavior/logic? │
│ ├─► v16: Use `extend_doctype_class` hook (PREFERRED) │
│ └─► v14/v15: Use `doc_events` hooks in hooks.py │
│ │
│ ► Override Jinja template? │
│ └─► Copy template to your app's templates/ folder │
│ └─► Register via `jinja.override_template` in hooks.py │
│ │
│ ► Add new DocType related to existing? │
│ └─► Create in your app's module │
│ └─► Link via Link field or Dynamic Link │
│ │
│ ► Add new workspace/menu items? │
│ └─► Create Workspace DocType in your app │
│ └─► Or use `standard_portal_menu_items` hook │
│ │
└─────────────────────────────────────────────────────────────────────────┘See: references/decision-tree.md for detailed extension patterns.Decision 3: Patch vs Fixture
┌─────────────────────────────────────────────────────────────────────────┐
│ SHOULD THIS BE A PATCH OR A FIXTURE? │
├─────────────────────────────────────────────────────────────────────────┤
│ │
│ Is it CONFIGURATION that should be the same everywhere? │
│ (Custom Fields, Roles, Workflows, Property Setters) │
│ └─► USE FIXTURE │
│ │
│ Is it a ONE-TIME data transformation? │
│ (Migrate old field values, cleanup bad data, populate defaults) │
│ └─► USE PATCH │
│ │
│ Does it need to run BEFORE schema changes? │
│ (Backup data from field that will be deleted) │
│ └─► USE PATCH with [pre_model_sync] │
│ │
│ Does it need to run AFTER schema changes? │
│ (Populate newly added field with calculated values) │
│ └─► USE PATCH with [post_model_sync] │
│ │
│ Is it master data / lookup tables? │
│ (Categories, Status options, Configuration records) │
│ └─► USE FIXTURE for initial, PATCH for updates │
│ │
└─────────────────────────────────────────────────────────────────────────┘See: references/decision-tree.md for patch timing flowchart.Decision 4: Module Organization
┌─────────────────────────────────────────────────────────────────────────┐
│ HOW MANY MODULES DO YOU NEED? │
├─────────────────────────────────────────────────────────────────────────┤
│ │
│ Small app (1-5 DocTypes, single purpose)? │
│ └─► ONE MODULE with app name │
│ Example: my_app/my_app/ (module "My App") │
│ │
│ Medium app (6-15 DocTypes, multiple areas)? │
│ └─► 2-4 MODULES by functional area │
│ Example: core/, settings/, integrations/ │
│ │
│ Large app (15+ DocTypes, complex domain)? │
│ └─► MODULES by business domain │
│ Example: inventory/, sales/, purchasing/, settings/ │
│ │
│ Multi-tenant or vertical solution? │
│ └─► Consider MULTIPLE APPS instead │
│ Base app + vertical-specific apps │
│ │
└─────────────────────────────────────────────────────────────────────────┘Rule: Each DocType belongs to EXACTLY one module. Choose module = where would a user look for this DocType?
Quick Implementation Workflows
New App Workflow
1. Create app structure → bench new-app my_app
2. Configure pyproject → Edit pyproject.toml (v15+) or setup.py (v14)
3. Define modules → Edit modules.txt
4. Create DocTypes → bench --site mysite new-doctype MyDocType
5. Write controllers → my_app/doctype/my_doctype/my_doctype.py
6. Configure hooks → hooks.py for integration
7. Export fixtures → bench --site mysite export-fixtures
8. Test installation → bench --site testsite install-app my_appSee: references/workflows.md for detailed steps.Patch Workflow
1. Plan the migration → What data moves where?
2. Choose timing → [pre_model_sync] or [post_model_sync]
3. Write patch file → myapp/patches/v1_0/description.py
4. Add to patches.txt → Under correct section
5. Test locally → bench --site testsite migrate
6. Handle errors → Add rollback logic if needed
7. Test on copy of prod → ALWAYS before productionSee: references/workflows.md for patch patterns.Fixture Workflow
1. Configure hooks.py → Define fixtures list with filters
2. Make changes via UI → Custom Fields, Property Setters, etc.
3. Export fixtures → bench --site mysite export-fixtures --app my_app
4. Verify JSON files → Check my_app/fixtures/*.json
5. Commit to version control
6. Test import → bench --site newsite migrateSee: references/workflows.md for fixture strategies.Version-Specific Considerations
| Aspect | v14 | v15 | v16 |
|---|---|---|---|
| Build config | setup.py | pyproject.toml | pyproject.toml |
| DocType extension | doc_events | doc_events | extend_doctype_class preferred |
| Python minimum | 3.10 | 3.10 | 3.11 |
| INI patches | ✅ | ✅ | ✅ |
| Fixtures format | JSON | JSON | JSON |
v16 Breaking Changes
extend_doctype_classhook: Cleaner DocType extension pattern- Data masking: Field-level privacy configuration available
- UUID naming: New naming rule option for DocTypes
- Chrome PDF: wkhtmltopdf deprecated for PDF generation
Critical Implementation Rules
✅ ALWAYS
- Start with
bench new-app- Never create structure manually - Define
__version__in__init__.py- Build will fail without it - Test patches on database copy - Never run untested patches on production
- Use batch processing - Any patch touching 1000+ records needs batching
- Filter fixtures - Never export all records of a DocType
- Version your patches - Use v1_0, v2_0 directories for organization
❌ NEVER
- Put frappe/erpnext in pyproject dependencies - They're not on PyPI
- Include transactional data in fixtures - Only configuration!
- Hardcode site-specific values - Use hooks or settings DocTypes
- Skip
frappe.db.commit()in large patches - Memory will explode - Delete fields without backup patch - Data loss is irreversible
- Modify core ERPNext files - Always use hooks or override patterns
Reference Files
| File | Contents |
|---|---|
references/decision-tree.md | Complete decision flowcharts |
references/workflows.md | Step-by-step implementation guides |
references/examples.md | Complete working examples |
references/anti-patterns.md | Common mistakes to avoid |
See Also
erpnext-syntax-customapp- Exact syntax referenceerpnext-syntax-hooks- Hooks configurationerpnext-impl-hooks- Hook implementation patternserpnext-database- Database operations for patches