Task results and status in Django - Mini Project: Build & Apply

Task Results and Status in Django

📖 Scenario: You are building a simple Django app to track tasks and their results. Each task has a name and a status that shows if it is pending, completed, or failed.

🎯 Goal: Create a Django model to store tasks with their results and status. Then, configure a status choice field, write a query to filter completed tasks, and finally add a method to display the task status nicely.

📋 What You'll Learn

Create a Django model named Task with fields name (CharField) and status (CharField).

Define a STATUS_CHOICES tuple with values 'pending', 'completed', and 'failed'.

Write a Django ORM query to get all tasks with status 'completed'.

Add a method get_status_display in the Task model to return a user-friendly status string.

💡 Why This Matters

🌍 Real World

Tracking task status is common in project management, bug tracking, and workflow automation apps.

💼 Career

Understanding Django models, choices, and queries is essential for backend web development jobs using Django.

1

Create the Task model with name and status fields

Create a Django model called Task with a name field as models.CharField(max_length=100) and a status field as models.CharField(max_length=20).

Django

# Define the Task model with name and status fields
# Your code here

Hint

Use models.CharField for both fields with the specified max_length values.

2

Add STATUS_CHOICES tuple and link it to the status field

Add a tuple called STATUS_CHOICES with these exact pairs: ('pending', 'Pending'), ('completed', 'Completed'), and ('failed', 'Failed'). Then update the status field to use choices=STATUS_CHOICES.

Django

from django.db import models

class Task(models.Model):
    name = models.CharField(max_length=100)
    # Add STATUS_CHOICES tuple and update status field choices
    # Your code here

Hint

Define STATUS_CHOICES as a tuple of tuples and pass it to the choices argument of the status field.

3

Write a query to get all completed tasks

Write a Django ORM query called completed_tasks that filters the Task model for all tasks where status is exactly 'completed'.

Django

from django.db import models

class Task(models.Model):
    STATUS_CHOICES = (
        ('pending', 'Pending'),
        ('completed', 'Completed'),
        ('failed', 'Failed'),
    )
    name = models.CharField(max_length=100)
    status = models.CharField(max_length=20, choices=STATUS_CHOICES)

# Write a query to get all completed tasks
# Your code here

Hint

Use Task.objects.filter(status='completed') to get all completed tasks.

4

Add a method to display the status nicely

Add a method called get_status_display inside the Task model that returns the display name of the current status using Django's built-in get_FOO_display() pattern.

Django

from django.db import models

class Task(models.Model):
    STATUS_CHOICES = (
        ('pending', 'Pending'),
        ('completed', 'Completed'),
        ('failed', 'Failed'),
    )
    name = models.CharField(max_length=100)
    status = models.CharField(max_length=20, choices=STATUS_CHOICES)

completed_tasks = Task.objects.filter(status='completed')

# Add get_status_display method inside Task
# Your code here

Hint

Implement the method using dict(self.STATUS_CHOICES).get(self.status, self.status) to get the display value.

Practice

1. In Django with Celery, which object do you use to check the status and result of a background task by its ID?

easy

A. AsyncResult

B. TaskStatus

C. TaskResult

D. ResultChecker

Solution

1. Step 1: Identify the object for task tracking

   Celery provides AsyncResult to track task status and results using the task ID.

2. Step 2: Confirm usage in Django context

   In Django projects using Celery, AsyncResult is the standard way to check if a task is pending, running, or finished.

3. Final Answer:

   AsyncResult -> Option A

4. Quick Check:

   Task status and results = AsyncResult [OK]

Hint: Remember: AsyncResult tracks task status by ID [OK]

Common Mistakes:

• Confusing AsyncResult with task function names
• Using non-existent classes like TaskStatus
• Trying to access results directly without AsyncResult

2. Which of the following is the correct way to create an AsyncResult instance for a task with ID stored in task_id?

easy

A. result = AsyncResult(task=task_id)

B. result = AsyncResult.get(task_id)

C. result = AsyncResult.fetch(task_id)

D. result = AsyncResult(task_id)

Solution

1. Step 1: Recall AsyncResult constructor usage

   The AsyncResult class is instantiated by passing the task ID as the first argument.

2. Step 2: Check each option's syntax

   Only AsyncResult(task_id) correctly creates the instance. Methods like .get() or .fetch() are not constructors.

3. Final Answer:

   result = AsyncResult(task_id) -> Option D

4. Quick Check:

   Instantiate AsyncResult with task ID directly [OK]

Hint: Use AsyncResult(task_id) to create result object [OK]

Common Mistakes:

• Calling get() or fetch() as constructor
• Passing keyword argument 'task' instead of positional
• Confusing AsyncResult with task function calls

3. Given the code:

result = AsyncResult('abc123')
status = result.status
output = result.result

What will status and output represent if the task is still running?

medium

A. status is 'PENDING', output is None

B. status is 'RUNNING', output is None

C. status is 'FAILURE', output is the error info

D. status is 'SUCCESS', output is the task result

Solution

1. Step 1: Understand AsyncResult status values

   By default, while a task is running without calling update_state inside the task, result.status remains 'PENDING'.

2. Step 2: Check result property during running

   result.result returns None until the task completes.

3. Final Answer:

   status is 'PENDING', output is None -> Option A

4. Quick Check:

   Running task (default): status='PENDING', result=None [OK]

Hint: Default running tasks show status 'PENDING' and result None [OK]

Common Mistakes:

• Mistaking for 'RUNNING' status (doesn't exist)
• Confusing with 'STARTED' which requires explicit update_state
• Thinking result is available before completion

4. You wrote:

result = AsyncResult(task_id)
if result.status == 'SUCCESS':
    print(result.result)
else:
    print('Task not done')

But it always prints 'Task not done' even after task completion. What is the likely issue?

medium

A. You must call result.get() instead of accessing result.result

B. You should check for 'COMPLETED' instead of 'SUCCESS'

C. The task ID is incorrect or expired

D. AsyncResult does not have a status attribute

Solution

1. Step 1: Understand status checking logic

   The code checks if result.status equals 'SUCCESS' to print the result.

2. Step 2: Identify why status never shows 'SUCCESS'

   If the task ID is wrong or expired, AsyncResult will not find the task and status stays 'PENDING' or similar.

3. Final Answer:

   The task ID is incorrect or expired -> Option C

4. Quick Check:

   Wrong task ID causes status never to be 'SUCCESS' [OK]

Hint: Check task ID validity if status never changes [OK]

Common Mistakes:

• Using wrong status string like 'COMPLETED'
• Assuming result.result always updates without completion
• Ignoring task ID correctness

5. You want to handle a task result in Django only if it succeeded, otherwise log the error. Which code snippet correctly checks the task status and safely accesses the result or error?

hard

A. result = AsyncResult(task_id)
if result.ready():
handle(result.result)
else:
log_error('Task not ready')

B. result = AsyncResult(task_id)
try:
handle(result.get(timeout=1))
except Exception as e:
log_error(e)

C. result = AsyncResult(task_id)
if result.status == 'PENDING':
handle(result.result)
else:
log_error('Task failed')

D. result = AsyncResult(task_id)
if result.status == 'SUCCESS':
handle(result.result)
elif result.status == 'FAILURE':
log_error(result.get())

Solution

1. Step 1: Understand safe result retrieval

   Using result.get() with a timeout waits for completion and raises exceptions on failure.

2. Step 2: Check error handling approach

   Wrapping result.get() in try-except catches task failures and allows logging errors safely.

3. Step 3: Compare other options

   Options B, C, and D do not handle exceptions properly; C incorrectly treats 'PENDING' as success.

4. Final Answer:

   Use try-except with result.get() to handle success and failure -> Option B

5. Quick Check:

   Use result.get() with try-except for safe task result handling [OK]

Hint: Use try-except with result.get() to catch errors [OK]

Common Mistakes:

• Checking only status strings without exception handling
• Assuming ready() means success
• Treating PENDING as success