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?
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┌─────────────────────────────────────────────────────────────────────────┐ │ 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?
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┌─────────────────────────────────────────────────────────────────────────┐ │ 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
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┌─────────────────────────────────────────────────────────────────────────┐ │ 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.mdfor detailed extension patterns.
Decision 3: Patch vs Fixture
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┌─────────────────────────────────────────────────────────────────────────┐ │ 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.mdfor patch timing flowchart.
Decision 4: Module Organization
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┌─────────────────────────────────────────────────────────────────────────┐ │ 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
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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_app
See:
references/workflows.mdfor detailed steps.
Patch Workflow
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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 production
See:
references/workflows.mdfor patch patterns.
Fixture Workflow
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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 migrate
See:
references/workflows.mdfor 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 reference - •
erpnext-syntax-hooks- Hooks configuration - •
erpnext-impl-hooks- Hook implementation patterns - •
erpnext-database- Database operations for patches