In a previous post, we explored how to manage scheduled tasks using IntervalSchedule through Django-Celery-Beat: Practical Examples of Scheduled Tasks with PeriodicTask.

However, in real-world projects, the interval execution mode alone is often insufficient.

• When tasks need to be executed at a specific time every day
• When a task needs to be executed only once at a specific date and time

In these cases, using the Crontab or Clocked scheduling methods allows for more precise task scheduling. 🚀

📌 Unfamiliar with the concept of Crontab?

➡️ Understanding Linux `crontab` Properly: Tips for Automatic Scheduling Loved by Developers

Reading the above article will help you understand better! 😊

1️⃣ Scheduling at Specific Times Using `CrontabSchedule`

Crontab is a scheduling method used in Linux that allows you to set tasks to run at specific intervals such as seconds/minutes/hours/days of the week/dates.

In Django-Celery-Beat, you can also set up scheduled tasks in the same way using `CrontabSchedule`.

📌 Example: A scheduled task that runs every day at 9:30 AM

from django_celery_beat.models import PeriodicTask, CrontabSchedule
import json

# 1️⃣ Create CrontabSchedule (executes every day at 09:30)
schedule, created = CrontabSchedule.objects.get_or_create(
    minute="30",
    hour="9",
    day_of_week="*",
    day_of_month="*",
    month_of_year="*"
)

# 2️⃣ Create or update a PeriodicTask
task, created = PeriodicTask.objects.update_or_create(
    name="daily_report_task",
    defaults={
        "crontab": schedule,  # Apply CrontabSchedule
        "task": "myapp.tasks.generate_daily_report",
        "args": json.dumps([]),
        "enabled": True,
    }
)

✅ The above configuration schedules the task to run every day at 9:30 AM! 🎯

✅ Explanation of `CrontabSchedule` Fields

2️⃣ Executing Once at a Specific Time Using `ClockedSchedule`

`ClockedSchedule` is used to set up scheduled tasks that run only once at a specific date and time.

📌 Example: A scheduled task that runs only once at a specific date (February 10, 2025, 15:00)

from django_celery_beat.models import PeriodicTask, ClockedSchedule
import json
from datetime import datetime

# 1️⃣ Create ClockedSchedule (executes on February 10, 2025, at 15:00)
scheduled_time = datetime(2025, 2, 10, 15, 0)  # Must use a datetime object!
schedule, created = ClockedSchedule.objects.get_or_create(
    clocked_time=scheduled_time
)

# 2️⃣ Create a PeriodicTask (set one_off=True!)
task, created = PeriodicTask.objects.update_or_create(
    name="one_time_task_20250210",
    defaults={
        "clocked": schedule,  # Apply ClockedSchedule
        "task": "myapp.tasks.one_time_email",
        "args": json.dumps([]),
        "enabled": True,
        "one_off": True,  # Automatically disable after execution
    }
)

✅ The above setting will run the task once at 15:00 on February 10, 2025 and will automatically disable itself afterwards.

• 📌 When creating an instance of the ClockedSchedule model, the clocked_time field must be input as a datetime object.
• 📌 Using a string or other data types may cause errors.

📌 Relationship Between ClockedSchedule and one_off Option?

When creating a task that executes only once using ClockedSchedule, you set one_off=True,
but you may wonder how this setting interacts with the enabled field.

📌 If you want to know more about the relationship between these two fields (clocked_time and one_off)?

➡️ The Relationship Between one-off and enabled in Celery Beat: Understanding and Usage

The above article discusses in-depth how `one_off=True` works and what differentiates it from `enabled`, so be sure to check it out! 😊

🎯 Conclusion: Crontab and Clocked Allow for More Precise Scheduled Tasks!

• Using CrontabSchedule allows you to schedule tasks that are periodic but executed at specific times!
• Using ClockedSchedule allows you to schedule tasks that are executed only once at specific points!
• When creating a ClockedSchedule, the clocked_time field must be input as a datetime object!
• There’s a separate post that covers the relationship between ClockedSchedule and one_off=True setting in more detail, so be sure to check it out!

If you want to learn more about leveraging Celery,

check the list of 'related posts' below or search for `"Celery"` in the search bar at the top right! 🚀 😊