frappe-impl-hooks

Frappe Hooks Implementation Workflow

Step-by-step workflows for implementing hooks.py configurations. For API syntax reference, see frappe-syntax-hooks.

Version: v14/v15/v16 (V16-specific features noted)

---

Master Decision: What Are You Implementing?

WHAT DO YOU WANT TO ACHIEVE?
│
├─► React to document lifecycle events?
│   ├─► On OTHER app's DocTypes → doc_events in hooks.py
│   ├─► On YOUR OWN DocTypes → controller methods (preferred)
│   └─► On ALL DocTypes → doc_events with "*" wildcard
│
├─► Run code on a schedule?
│   └─► scheduler_events (daily, hourly, cron, etc.)
│
├─► Modify an existing DocType's behavior?
│   ├─► V16+: extend_doctype_class (RECOMMENDED)
│   └─► V14/V15: override_doctype_class (last app wins!)
│
├─► Override an existing API endpoint?
│   └─► override_whitelisted_methods
│
├─► Add custom permission logic?
│   ├─► List filtering → permission_query_conditions
│   └─► Document-level → has_permission
│
├─► Send config data to client on page load?
│   └─► extend_bootinfo
│
├─► Export/import configuration?
│   └─► fixtures
│
├─► Add JS/CSS to desk or portal?
│   ├─► Desk-wide → app_include_js / app_include_css
│   ├─► Portal-wide → web_include_js / web_include_css
│   └─► Specific form → doctype_js
│
├─► Customize website/portal behavior?
│   └─► website_context, portal_menu_items, website_route_rules
│
└─► Hook into session/auth lifecycle?
    └─► on_login, on_session_creation, on_logout

---

Workflow 1: Implementing doc_events

When to Use

Use doc_events when you need to react to document lifecycle events on DocTypes owned by OTHER apps (ERPNext, Frappe core). For YOUR OWN DocTypes, ALWAYS prefer controller methods.

Step-by-Step

Step 1: Choose the right event (see references/decision-tree.md)

BEFORE save: validate (every save), before_insert (new only)
AFTER save:  after_insert (new only), on_update (every save), on_change (any change)
SUBMIT flow: before_submit → on_submit → on_change
CANCEL flow: before_cancel → on_cancel → on_change
DELETE:      on_trash (before), after_delete (after)
RENAME:      before_rename, after_rename

Step 2: Add to hooks.py

# myapp/hooks.py
doc_events = {
    "Sales Invoice": {
        "validate": "myapp.events.sales_invoice.validate",
        "on_submit": "myapp.events.sales_invoice.on_submit"
    }
}

Step 3: Create handler module

# myapp/events/sales_invoice.py
import frappe

def validate(doc, method=None):
    """Changes to doc ARE saved (before-save event)."""
    if doc.grand_total < 0:
        frappe.throw("Total cannot be negative")

def on_submit(doc, method=None):
    """Document already saved. Use db_set_value for changes."""
    frappe.db.set_value("Sales Invoice", doc.name,
                        "custom_external_id", create_external(doc))

Step 4: Deploy

bench --site sitename migrate

Step 5: Test

bench --site sitename execute myapp.events.sales_invoice.validate --kwargs '{"doc_name": "INV-001"}'
# Or in bench console:
# doc = frappe.get_doc("Sales Invoice", "INV-001"); doc.save()

Critical Rules for doc_events

• NEVER call frappe.db.commit() inside a doc_event handler — Frappe manages the transaction
• NEVER modify doc fields in on_update — changes are lost; use frappe.db.set_value() instead
• ALWAYS accept method=None as second parameter in handler signature
• ALWAYS use rename signature: def handler(doc, method, old, new, merge)
• ALWAYS run bench --site sitename migrate after changing hooks.py

---

Workflow 2: Implementing scheduler_events

Step-by-Step

Step 1: Choose frequency

Frequency	Short (< 5 min)	Long (5-25 min)
Every tick	all	—
Hourly	hourly	hourly_long
Daily	daily	daily_long
Weekly	weekly	weekly_long
Monthly	monthly	monthly_long
Custom	cron	cron (use long queue manually)

Step 2: Add to hooks.py

scheduler_events = {
    "daily": ["myapp.tasks.daily_cleanup"],
    "daily_long": ["myapp.tasks.heavy_sync"],
    "cron": {
        "0 9 * * 1-5": ["myapp.tasks.weekday_report"]
    }
}

Step 3: Implement task (NO arguments)

# myapp/tasks.py
import frappe

def daily_cleanup():
    """Scheduler calls with NO arguments."""
    frappe.db.delete("Error Log", {
        "creation": ["<", frappe.utils.add_days(None, -30)]
    })
    frappe.db.commit()

def heavy_sync():
    """Long task — commit periodically."""
    records = get_records_to_sync()
    for i, record in enumerate(records):
        process(record)
        if i % 100 == 0:
            frappe.db.commit()
    frappe.db.commit()

Step 4: Deploy and verify

bench --site sitename migrate
bench --site sitename scheduler enable
bench --site sitename scheduler status
# Test manually:
bench --site sitename execute myapp.tasks.daily_cleanup

Critical Rules for Scheduler

• NEVER add parameters to scheduler task functions — the scheduler passes none
• ALWAYS use _long variants for tasks exceeding 5 minutes (default queue timeout is 5 min)
• ALWAYS commit periodically in long tasks to save progress
• Tasks > 25 minutes: split into chunks or use frappe.enqueue()

---

Workflow 3: Implementing extend_doctype_class (V16+)

Step-by-Step

Step 1: Add to hooks.py

extend_doctype_class = {
    "Sales Invoice": ["myapp.extensions.sales_invoice.SalesInvoiceMixin"]
}

Step 2: Create mixin class

# myapp/extensions/sales_invoice.py
import frappe
from frappe.model.document import Document

class SalesInvoiceMixin(Document):
    def validate(self):
        super().validate()  # ALWAYS call super() FIRST
        self.custom_validation()

    def custom_validation(self):
        if self.grand_total > 1000000:
            frappe.msgprint("High-value invoice", indicator="orange")

Step 3: Deploy — bench --site sitename migrate

When to Use extend vs override

• ALWAYS prefer extend_doctype_class on V16+ — multiple apps can extend safely
• ONLY use override_doctype_class when you must completely replace controller logic
• On V14/V15, override_doctype_class is the only option — last installed app wins

---

Workflow 4: Implementing Permission Hooks

Step-by-Step

Step 1: Add to hooks.py

permission_query_conditions = {
    "Sales Invoice": "myapp.permissions.si_query"
}
has_permission = {
    "Sales Invoice": "myapp.permissions.si_permission"
}

Step 2: Implement handlers

# myapp/permissions.py
import frappe

def si_query(user):
    """Returns SQL WHERE clause for list filtering."""
    if not user:
        user = frappe.session.user
    if "Sales Manager" in frappe.get_roles(user):
        return ""  # See all
    return f"`tabSales Invoice`.owner = {frappe.db.escape(user)}"

def si_permission(doc, user=None, permission_type=None):
    """Returns True (allow), False (deny), or None (use default)."""
    if not user:
        user = frappe.session.user
    if permission_type == "write" and doc.status == "Closed":
        return False
    return None

Critical Rules for Permission Hooks

• permission_query_conditions ONLY works with get_list, NEVER with get_all
• has_permission can ONLY deny access — returning True does NOT grant additional permissions
• ALWAYS handle user=None by defaulting to frappe.session.user

---

Workflow 5: Asset Injection and doctype_js

Adding Global JS/CSS

# hooks.py
app_include_js = "/assets/myapp/js/myapp.min.js"       # Desk
app_include_css = "/assets/myapp/css/myapp.min.css"     # Desk
web_include_js = "/assets/myapp/js/portal.min.js"       # Portal
web_include_css = "/assets/myapp/css/portal.min.css"    # Portal

Extending a Specific Form

# hooks.py
doctype_js = {
    "Sales Invoice": "public/js/sales_invoice.js"
}

// myapp/public/js/sales_invoice.js
frappe.ui.form.on("Sales Invoice", {
    refresh(frm) {
        if (frm.doc.docstatus === 1) {
            frm.add_custom_button(__("Custom Action"), () => {
                frappe.call({
                    method: "myapp.api.custom_action",
                    args: { invoice: frm.doc.name },
                    freeze: true
                });
            }, __("Actions"));
        }
    }
});

ALWAYS run bench build --app myapp after changing JS/CSS files.

---

Workflow 6: Fixtures, Boot Info, and Website Hooks

Fixtures

fixtures = [
    {"dt": "Custom Field", "filters": [["module", "=", "My App"]]},
    {"dt": "Property Setter", "filters": [["module", "=", "My App"]]}
]

NEVER export fixtures without filters — it captures ALL apps' customizations.

extend_bootinfo

extend_bootinfo = "myapp.boot.extend_with_config"

def extend_with_config(bootinfo):
    bootinfo.my_app = {"feature_enabled": True}
    # NEVER send secrets — bootinfo is visible in browser DevTools

Website Hooks

website_route_rules = [
    {"from_route": "/shop/<category>", "to_route": "shop"}
]
portal_menu_items = [
    {"title": "My Orders", "route": "/my-orders", "role": "Customer"}
]
on_login = "myapp.handlers.on_login"
on_logout = "myapp.handlers.on_logout"

---

Migration: Moving Logic Between Hooks, Controllers, and Server Scripts

From	To	Steps
Server Script → hooks.py	1. Create Python handler, 2. Add doc_events, 3. Disable Server Script, 4. Migrate
hooks.py → Controller	1. Move logic to doctype .py, 2. Remove doc_events entry, 3. Migrate
Controller → hooks.py	1. Create events module, 2. Add doc_events, 3. Remove from controller, 4. Migrate

ALWAYS migrate after ANY hooks.py change: bench --site sitename migrate

---

Handler Signatures Quick Reference

Hook	Signature
doc_events	def handler(doc, method=None):
rename events	def handler(doc, method, old, new, merge):
scheduler_events	def handler(): (no args)
extend_bootinfo	def handler(bootinfo):
permission_query	def handler(user): returns SQL string
has_permission	def handler(doc, user=None, permission_type=None): returns True/False/None
on_login	def handler(login_manager):
on_logout	def handler():

---

Version Differences

Feature	V14	V15	V16
doc_events	Yes	Yes	Yes
scheduler_events	Yes	Yes	Yes
override_doctype_class	Yes	Yes	Yes
extend_doctype_class	No	No	Yes
permission hooks	Yes	Yes	Yes
Scheduler tick interval	~4 min	~4 min	~60 sec
auth_hooks	No	Yes	Yes

---

Reference Files

File	Contents
decision-tree.md	Complete hook selection flowcharts
workflows.md	Step-by-step implementation patterns
examples.md	Working code examples for all hook types