seitime-frappe/frappe/docs/user/en/tutorial/task-runner.md

Scheduled Tasks

Finally, an application also has to send email notifications and do other kind of scheduled tasks. In Frappe, if you have setup the bench, the task / scheduler is setup via Celery using Redis Queue.

To add a new task handler, go to hooks.py and add a new handler. Default handlers are all, daily, weekly, monthly. The all handler is called every 3 minutes by default.

# Scheduled Tasks
# ---------------

scheduler_events = {
	"daily": [
		"library_management.tasks.daily"
	],
}

Here we can point to a Python function and that function will be executed every day. Let us look what this function looks like:

# Copyright (c) 2013, Frappe
# For license information, please see license.txt

from __future__ import unicode_literals
import frappe
from frappe.utils import datediff, nowdate, format_date, add_days

def daily():
	loan_period = frappe.db.get_value("Library Management Settings",
		None, "loan_period")

	overdue = get_overdue(loan_period)

	for member, items in overdue.iteritems():
		content = """<h2>Following Items are Overdue</h2>
		<p>Please return them as soon as possible</p><ol>"""

		for i in items:
			content += "<li>{0} ({1}) due on {2}</li>".format(i.article_name,
				i.article,
				format_date(add_days(i.transaction_date, loan_period)))

		content += "</ol>"

		recipient = frappe.db.get_value("Library Member", member, "email_id")
		frappe.sendmail(recipients=[recipient],
			sender="test@example.com",
			subject="Library Articles Overdue", content=content, bulk=True)

def get_overdue(loan_period):
	# check for overdue articles
	today = nowdate()

	overdue_by_member = {}
	articles_transacted = []

	for d in frappe.db.sql("""select name, article, article_name,
		library_member, member_name
		from `tabLibrary Transaction`
		order by transaction_date desc, modified desc""", as_dict=1):

		if d.article in articles_transacted:
			continue

		if d.transaction_type=="Issue" and \
			datediff(today, d.transaction_date) > loan_period:
			overdue_by_member.setdefault(d.library_member, [])
			overdue_by_member[d.library_member].append(d)

		articles_transacted.append(d.article)

We can place the above code code in any accessible Python module. The route is defined in hooks.py, so for our purposes we would place this code in library_management/tasks.py.

Note:

1. We get the loan period from Library Management Settings by using frappe.db.get_value.
2. We run a query in the database with frappe.db.sql
3. Email is sent via frappe.sendmail

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