Skip to main content

Documentation Index

Fetch the complete documentation index at: https://mintlify.com/frappe/erpnext/llms.txt

Use this file to discover all available pages before exploring further.

ERPNext is built on top of the Frappe Framework, a full-stack web application framework written in Python and JavaScript. Understanding the architecture is essential for extending and customizing ERPNext.

​
Framework Architecture

ERPNext follows a modular, metadata-driven architecture that separates business logic from the framework layer.
1

Application Layer

ERPNext is organized into modules (Accounts, Stock, Selling, Buying, Manufacturing, etc.) that contain business logic and domain-specific functionality.
2

Framework Layer

Frappe Framework provides the foundation: ORM, routing, authentication, background jobs, websockets, and API infrastructure.
3

Database Layer

Uses MariaDB/MySQL with a metadata-driven schema. DocTypes define the data model dynamically.

​
Core Architectural Patterns

​
1. Metadata-Driven Design

ERPNext uses JSON metadata files to define DocTypes (data models). The framework reads these definitions and generates database tables, forms, and APIs automatically. 
# DocType metadata is stored in JSON files
# Example: sales_order.json defines the Sales Order structure
{
  "doctype": "DocType",
  "name": "Sales Order",
  "autoname": "naming_series:",
  "fields": [
    {
      "fieldname": "customer",
      "fieldtype": "Link",
      "options": "Customer",
      "reqd": 1
    }
  ]
}

​
2. Controller Pattern

Each DocType has a corresponding Python controller class that inherits from Document or specialized controllers. 
# sales_order.py
from frappe.model.document import Document

class SalesOrder(Document):
    def validate(self):
        """Called before saving the document"""
        self.calculate_totals()
        self.validate_delivery_date()
    
    def on_submit(self):
        """Called when document is submitted"""
        self.update_stock_reservation()
        self.create_gl_entries()

​
3. Module Structure

ERPNext follows a consistent directory structure: 
erpnext/
├── accounts/          # Accounting module
│   ├── doctype/
│   │   ├── sales_invoice/
│   │   │   ├── sales_invoice.json    # Metadata
│   │   │   ├── sales_invoice.py      # Controller
│   │   │   ├── sales_invoice.js      # Client-side logic
│   │   │   └── test_sales_invoice.py # Tests
│   ├── report/        # Reports
│   └── page/          # Custom pages
├── stock/             # Inventory management
├── selling/           # Sales module
├── buying/            # Procurement module
├── manufacturing/     # Production module
├── controllers/       # Shared controllers
│   ├── accounts_controller.py
│   ├── selling_controller.py
│   └── stock_controller.py
└── hooks.py          # App configuration

​
Document Lifecycle

Understanding the document lifecycle is crucial for implementing business logic:
1

Draft (docstatus = 0)

Document is being created/edited. Can be modified freely.
2

Submitted (docstatus = 1)

Document is finalized and locked. Creates ledger entries and affects other documents.
3

Cancelled (docstatus = 2)

Document is reversed. Reverses ledger entries and linked transactions.

​
Document Events

Framework provides hooks at every stage of document lifecycle: 
class SalesOrder(SellingController):
    def validate(self):
        """Before save (draft/submit)"""
        pass
    
    def before_save(self):
        """Just before saving to database"""
        pass
    
    def on_update(self):
        """After save to database"""
        pass
    
    def before_submit(self):
        """Before submission"""
        pass
    
    def on_submit(self):
        """After successful submission"""
        pass
    
    def on_cancel(self):
        """When document is cancelled"""
        pass
    
    def on_trash(self):
        """Before document is deleted"""
        pass

​
API Architecture

​
Whitelisted Methods

Expose server-side methods as REST/RPC endpoints: 
import frappe

@frappe.whitelist()
def get_customer_outstanding(customer):
    """Callable via /api/method/erpnext.accounts.utils.get_customer_outstanding"""
    return frappe.db.get_value(
        "Sales Invoice",
        {"customer": customer, "docstatus": 1},
        "sum(outstanding_amount)"
    )

​
Permission System

Role-based permissions are defined in DocType metadata and enforced automatically: 
# Check permissions in code
if frappe.has_permission("Sales Order", "write", doc):
    doc.save()

# User permissions filter data
frappe.get_all("Sales Order", filters={"customer": "CUST-001"})
# Returns only orders the user has permission to see

​
Regional Customization

ERPNext supports region-specific overrides without modifying core code: 
# From erpnext/__init__.py
import erpnext

@erpnext.allow_regional
def calculate_taxes(doc):
    """Default tax calculation"""
    return standard_tax_calculation(doc)

# In hooks.py, override for specific regions
regional_overrides = {
    "India": {
        "erpnext.controllers.taxes.calculate_taxes": 
            "erpnext.regional.india.calculate_gst"
    }
}

​
Performance Patterns

ERPNext includes several patterns for optimal performance:
  • Caching: frappe.cache() for frequently accessed data
  • Background Jobs: Use frappe.enqueue() for long-running tasks
  • Query Optimization: Use qb (query builder) instead of raw SQL
  • Batch Processing: Process large datasets in chunks

​
Query Builder Example

from frappe import qb
from frappe.query_builder.functions import Sum

# Type-safe query building
SalesInvoice = qb.DocType("Sales Invoice")
query = (
    qb.from_(SalesInvoice)
    .select(SalesInvoice.customer, Sum(SalesInvoice.grand_total))
    .where(SalesInvoice.docstatus == 1)
    .groupby(SalesInvoice.customer)
)
results = query.run(as_dict=True)

​
Key Utilities

​
Database Operations

import frappe

# Get single value
company = frappe.db.get_value("Sales Order", "SO-001", "company")

# Get document
doc = frappe.get_doc("Sales Order", "SO-001")

# Create new document
doc = frappe.get_doc({
    "doctype": "Sales Order",
    "customer": "CUST-001",
    "items": [{"item_code": "ITEM-001", "qty": 10}]
})
doc.insert()

# Update
frappe.db.set_value("Sales Order", "SO-001", "status", "Completed")

​
Validation Helpers

from frappe import _

def validate(self):
    # Throw user-friendly error
    if not self.delivery_date:
        frappe.throw(_("Delivery Date is mandatory"))
    
    # Validation with specific exception type
    if self.total_qty < 0:
        frappe.throw(
            _("Quantity cannot be negative"),
            exc=InvalidQtyError
        )

​
Next Steps

DocType System

Learn how to create and customize DocTypes

Hooks

Extend ERPNext using hooks

Testing

Write tests for your customizations

API Reference

Explore the complete API

Build docs developers (and LLMs) love

Get started for freeTalk to us