frappe-syntax-controllers

name	frappe-syntax-controllers
description	Use when writing Python Document Controllers for ERPNext/Frappe DocTypes. Covers lifecycle hooks (validate, on_update, on_submit), controller override, submittable documents, autoname patterns, UUID naming (v16), and the flags system. Keywords: document controller, lifecycle hook, validate, on_update, on_submit, autoname, naming series, flags, v14-v16, controller example, lifecycle hook order, when to use validate, Python DocType class.
license	MIT
compatibility	Claude Code, Claude.ai Projects, Claude API. Frappe v14-v16.
metadata	{"author":"OpenAEC-Foundation","version":"2.0"}

Frappe Syntax: Document Controllers

Document Controllers are Python classes that define all server-side logic for a DocType. EVERY DocType has exactly one controller file. The controller class extends frappe.model.document.Document.

Quick Reference

import frappe
from frappe import _
from frappe.model.document import Document

class SalesOrder(Document):
    def autoname(self):
        """Custom naming logic. Sets self.name."""
        self.name = f"SO-{self.customer_code}-{frappe.utils.now_datetime().year}"

    def validate(self):
        """MAIN validation — runs on EVERY save (insert and update).
        Changes to self ARE saved to database."""
        if not self.items:
            frappe.throw(_("Items are required"))
        self.total = sum(item.amount for item in self.items)

    def on_update(self):
        """After save — changes to self are NOT saved.
        Use frappe.db.set_value() for post-save field changes."""
        self.notify_linked_docs()

    def on_submit(self):
        """After submit (docstatus 0 -> 1). Create ledger entries here."""
        self.create_gl_entries()

    def on_cancel(self):
        """After cancel (docstatus 1 -> 2). Reverse ledger entries here."""
        self.reverse_gl_entries()

    @frappe.whitelist()
    def recalculate(self):
        """Exposed to client JS via frm.call('recalculate')."""
        self.total = sum(item.amount for item in self.items)
        return {"total": self.total}

File Location and Naming

DocType Name	Class Name	File Path
Sales Order	SalesOrder	selling/doctype/sales_order/sales_order.py
My Custom Doc	MyCustomDoc	module/doctype/my_custom_doc/my_custom_doc.py

Rule: DocType name -> PascalCase class -> snake_case filename. ALWAYS match exactly.

---

Lifecycle Hook Execution Order

INSERT (new document)

before_insert -> before_naming -> autoname -> before_validate -> validate
-> before_save -> [db_insert] -> after_insert -> on_update -> on_change

SAVE (existing document)

before_validate -> validate -> before_save -> [db_update]
-> on_update -> on_change

SUBMIT (docstatus 0 -> 1)

before_validate -> validate -> before_submit -> [db_update]
-> on_submit -> on_update -> on_change

CANCEL (docstatus 1 -> 2)

before_cancel -> [db_update] -> on_cancel -> on_change

UPDATE AFTER SUBMIT

before_update_after_submit -> [db_update]
-> on_update_after_submit -> on_change

DELETE

on_trash -> [db_delete] -> after_delete

DISCARD [v15+]

before_discard -> [db_set docstatus=2] -> on_discard

Complete hook reference with parameters: See lifecycle-methods.md

---

Hook Selection Decision Tree

What do you need to do?
|
+-- Validate data or calculate fields?
|   +-- validate (changes to self ARE saved)
|
+-- Action AFTER save (emails, sync, linked docs)?
|   +-- on_update (changes to self are NOT saved)
|
+-- Only for NEW documents?
|   +-- after_insert (runs once on first save only)
|
+-- Custom document name?
|   +-- autoname (set self.name)
|
+-- Before/after SUBMIT?
|   +-- Validate before submit? -> before_submit
|   +-- Create entries after submit? -> on_submit
|
+-- Before/after CANCEL?
|   +-- Check linked docs? -> before_cancel
|   +-- Reverse entries? -> on_cancel
|
+-- Cleanup before delete?
|   +-- on_trash
|
+-- React to ANY value change (including db_set)?
|   +-- on_change (MUST be idempotent)

---

Critical Rules

1. Changes after on_update are NOT saved

# WRONG - change is lost after on_update
def on_update(self):
    self.status = "Completed"  # NOT saved to database

# CORRECT - use db_set or frappe.db.set_value
def on_update(self):
    self.db_set("status", "Completed")

2. NEVER call frappe.db.commit() in controllers

# WRONG - breaks Frappe transaction management
def validate(self):
    frappe.db.commit()  # Can cause partial updates on error

# CORRECT - Frappe commits automatically at end of request
def validate(self):
    self.update_related()  # No commit needed

3. ALWAYS call super() when overriding

# WRONG - parent validation is skipped entirely
def validate(self):
    self.custom_check()

# CORRECT - parent logic preserved
def validate(self):
    super().validate()
    self.custom_check()

4. Use flags for recursion prevention

def on_update(self):
    if self.flags.get("from_linked_doc"):
        return
    linked = frappe.get_doc("Linked Doc", self.linked_doc)
    linked.flags.from_linked_doc = True
    linked.save()

5. NEVER put validation logic in on_update

# WRONG - document is already saved when this throws
def on_update(self):
    if self.total < 0:
        frappe.throw("Invalid total")  # Too late!

# CORRECT - validate BEFORE save
def validate(self):
    if self.total < 0:
        frappe.throw("Invalid total")  # Blocks save

---

Document Naming (autoname)

Method	Example	Result	Version
field:fieldname	field:customer_name	ABC Company	All
naming_series:	naming_series:	SO-2024-00001	All
Expression	PRE-.#####	PRE-00001	All
Old-style format	INV-{YYYY}-{####}	INV-2024-0001	Deprecated v16
hash / random	hash	a1b2c3d4e5	All
Prompt	Prompt	User enters name	All
autoincrement	autoincrement	1, 2, 3	All
UUID	UUID	550e8400-e29b-...	v16+
Custom method	autoname() in controller	Any pattern	All

Custom autoname Method

from frappe.model.naming import getseries

class Project(Document):
    def autoname(self):
        prefix = f"P-{self.customer[:3].upper()}-"
        self.name = getseries(prefix, 3)
        # Result: P-ACM-001, P-ACM-002, etc.

UUID Naming [v16+]

Set autoname = "UUID" in DocType definition. Frappe generates UUID v4.

When to use UUID:              When to use traditional naming:
- Cross-system sync            - User-facing references (SO-00001)
- Bulk record creation         - Sequential numbering required
- Global uniqueness needed     - Auditing requires readable names

---

Controller Extension Mechanisms

1. override_doctype_class (full replacement) [All versions]

# hooks.py
override_doctype_class = {
    "Sales Order": "custom_app.overrides.CustomSalesOrder"
}

# custom_app/overrides.py
from erpnext.selling.doctype.sales_order.sales_order import SalesOrder

class CustomSalesOrder(SalesOrder):
    def validate(self):
        super().validate()  # ALWAYS call super()
        self.custom_validation()

WARNING: Only ONE app can override a DocType class. Multiple overrides conflict.

2. extend_doctype_class (mixin, non-destructive) [v16+]

# hooks.py
extend_doctype_class = {
    "Address": ["custom_app.extensions.address.GeocodingMixin"],
    "Contact": [
        "custom_app.extensions.common.ValidationMixin",
        "custom_app.extensions.contact.PhoneMixin"
    ]
}

# custom_app/extensions/address.py
from frappe.model.document import Document

class GeocodingMixin(Document):
    @property
    def full_address(self):
        return f"{self.address_line1}, {self.city}, {self.country}"

    def validate(self):
        super().validate()
        self.geocode_address()

ALWAYS prefer extend_doctype_class over override_doctype_class in v16+. Multiple apps can safely extend the same DocType.

3. doc_events (hook individual events) [All versions]

# hooks.py
doc_events = {
    "Sales Order": {
        "validate": "custom_app.events.validate_sales_order",
        "on_submit": "custom_app.events.on_submit_sales_order"
    },
    "*": {  # ALL DocTypes
        "after_insert": "custom_app.events.log_creation"
    }
}

# custom_app/events.py
def validate_sales_order(doc, method=None):
    if doc.total > 100000:
        doc.requires_approval = 1

When to Use Which

Need full class replacement?     -> override_doctype_class [all versions]
Need to add methods/properties?  -> extend_doctype_class [v16+]
Need to hook one or two events?  -> doc_events [all versions]
Need to extend in v14/v15?       -> override_doctype_class or doc_events

---

Whitelisted Methods

Expose controller methods to client-side JavaScript with @frappe.whitelist():

class SalesOrder(Document):
    @frappe.whitelist()
    def send_email(self, recipient):
        """Callable from JS: frm.call('send_email', {recipient: '...'})"""
        frappe.sendmail(recipients=[recipient], message="Order confirmed")
        return {"status": "sent"}

// Client-side call
frm.call('send_email', { recipient: '[e-mail]' })
    .then(r => frappe.msgprint(r.message.status));

Rules:

• ALWAYS add @frappe.whitelist() decorator — without it, the method is NOT callable from client
• The method MUST be defined on the controller class (not standalone)
• Permission checks happen automatically (user must have read access to the document)

---

Submittable Documents

Documents with is_submittable = 1 follow the docstatus lifecycle:

docstatus	State	Editable	Transitions
0	Draft	Yes	-> 1 (Submit)
1	Submitted	Only "Allow on Submit" fields	-> 2 (Cancel)
2	Cancelled	No	None (amend creates new Draft)

ALWAYS implement both on_submit and on_cancel as a pair. ALWAYS reverse in on_cancel what on_submit created.

---

Inheritance Patterns

# Standard controller
from frappe.model.document import Document
class MyDoc(Document): pass

# Tree DocType (hierarchical)
from frappe.utils.nestedset import NestedSet
class Department(NestedSet):
    nsm_parent_field = "parent_department"

# Virtual DocType (no database table)
class ExternalData(Document):
    def load_from_db(self): ...
    def db_insert(self, *args, **kwargs): ...
    def db_update(self, *args, **kwargs): ...
    @staticmethod
    def get_list(args): ...
    @staticmethod
    def get_count(args): ...

---

Type Annotations [v15+]

class Person(Document):
    if TYPE_CHECKING:
        from frappe.types import DF
        first_name: DF.Data
        last_name: DF.Data
        birth_date: DF.Date
        company: DF.Link

Enable auto-generation in hooks.py: export_python_type_annotations = True

---

Version Differences

Feature	v14	v15	v16
Type annotations	No	Auto-generated	Yes
before_discard / on_discard	No	Yes	Yes
flags.notify_update	No	Yes	Yes
extend_doctype_class	No	No	Yes
UUID autoname	No	No	Yes
Old-style format naming	Yes	Yes	Deprecated

---

Reference Files

File	Contents
lifecycle-methods.md	All hooks with execution order diagrams
document-api-complete.md	Complete Document API: all methods by category (CRUD, fields, DB, permissions, flags, child tables, naming)
methods.md	Document class method signatures
events.md	All document events in order
examples.md	Complete working controller examples
anti-patterns.md	Common mistakes and corrections
flags.md	Flags system (doc.flags, frappe.flags)
hooks.md	Controller interaction with hooks.py
patterns.md	Common controller patterns
syntax.md	Controller class syntax reference

Related Skills

• frappe-syntax-serverscripts -- Server Scripts (sandbox alternative)
• frappe-syntax-hooks -- hooks.py configuration
• frappe-impl-controllers -- Implementation workflows
• frappe-core-permissions -- Permission system