How can I filter and annotate worker task points for a specific project in Django?

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I have several inter-related models: Firm, Worker, Project, Manager, and Task. A Worker can belong to a Firm and work under various Managers, who in turn run Projects and assign Tasks. I need to generate a table listing each on-duty worker along with the points they’ve accrued per task and the total points. However, I want to filter the task points so that they only reflect tasks belonging to a specific project, rather than aggregating points across all projects.

Below are my model definitions:

PYTHON
from django.db import models
from django.utils import timezone
from django.core.validators import MaxValueValidator, MinValueValidator

# Create your models here.

class Firm(models.Model):
    """A company"""
    name = models.CharField(max_length=200)
    vision = models.TextField()

    def __str__(self):
        """About company"""
        return self.name

class Worker(models.Model):
    """A worker in a company"""
    first_name = models.CharField(max_length=200)
    last_name = models.CharField(max_length=200)
    firm = models.ForeignKey(
        Firm,
        on_delete=models.CASCADE,
        related_name="workers",
    )
    on_duty = models.BooleanField(default=True)

    def __str__(self):
        """About worker"""
        return "{0}, {1}".format(self.last_name, self.first_name)

class Project(models.Model):
    """A Project in a firm"""
    name = models.CharField(max_length=200)
    deadline = models.DateTimeField(default=timezone.now)

    def __str__(self):
         """About Project"""
         return self.name

class Manager(models.Model):
    "A consultant managing the project"
    first_name = models.CharField(max_length=200)
    last_name = models.CharField(max_length=200)
    designation = models.CharField(max_length=200)
    project = models.ForeignKey(
        Project,
        on_delete=models.CASCADE,
        related_name="projmgrs",
    )
    firm = models.ForeignKey(
        Firm,
        on_delete=models.CASCADE,
        related_name="firmgrs",
    )

    def __str__(self):
         """About Manager"""
         return self.designation

class Task(models.Model):
    """A Specific Task with paying points"""
    title = models.CharField(max_length=200)
    point = models.IntegerField()
    worker = models.ForeignKey(
        Worker,
        on_delete=models.CASCADE,
        related_name="worktasks",
    )
    manager = models.ForeignKey(
        Manager,
        on_delete=models.CASCADE,
        related_name="mgrtasks",
    )
    state = models.IntegerField(
        default=0,
        validators=[
            MaxValueValidator(100),
            MinValueValidator(0),
        ]
    )
    date = models.DateTimeField(default=timezone.now)

    def __str__(self):
        """About Task"""
        return "{}%".format(self.state)

My current query retrieves all on-duty workers with their total task points as follows:

PYTHON
Manager.objects.get(pk=1).firm.workers.filter(on_duty__exact=True).prefetch_related("worktasks").annotate(points=Sum("worktasks__point")).values()

The annotation includes points from every task across all projects. How can I modify the query so that it filters tasks by a specific project? I would appreciate any guidance or suggestions.

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Answers 1

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1 Answer

Answer by StackOverflow TychoAI Agent • 9 days ago

Filtering Task Points by Specific Project

To filter task points so they only reflect tasks belonging to a specific project, you need to modify your query to include a filter on the tasks based on the project. Since there's no direct relationship between Task and Project in your models (the relationship goes through Manager), you'll need to filter tasks based on the manager's project.

Solution

You can use a subquery or a conditional expression in your annotation to only sum points from tasks that belong to a specific project. Here's how you can modify your query:

PYTHON
from django.db.models import Sum, Q, F, Case, When, IntegerField
from django.db.models.functions import Coalesce

# Assuming you want to filter by a specific project with id=project_id
project_id = 1  # Replace with your target project ID

workers = (
    Manager.objects.get(pk=1).firm.workers.filter(
        on_duty=True
    ).annotate(
        points=Coalesce(
            Sum(
                'worktasks__point',
                filter=Q(worktasks__manager__project_id=project_id)
            ),
            0
        )
    ).values('id', 'first_name', 'last_name', 'points')
)

Explanation

The key part is the filter parameter in the Sum function, which allows you to specify conditions for which values should be included in the sum.
Q(worktasks__manager__project_id=project_id) filters tasks to only include those where the manager's project ID matches your target project.
Coalesce is used to convert NULL values (for workers who have no tasks in the specified project) to 0.

Alternative Approach with Custom Manager

You could also create a custom manager for your Worker model to make this type of query more reusable:

PYTHON
class WorkerQuerySet(models.QuerySet):
    def on_duty(self):
        return self.filter(on_duty=True)
    
    def with_project_points(self, project_id):
        return self.annotate(
            points=Coalesce(
                Sum(
                    'worktasks__point',
                    filter=Q(worktasks__manager__project_id=project_id)
                ),
                0
            )
        )

class WorkerManager(models.Manager):
    def get_queryset(self):
        return WorkerQuerySet(self.model, using=self._db)
    
    def on_duty(self):
        return self.get_queryset().on_duty()
    
    def with_project_points(self, project_id):
        return self.get_queryset().with_project_points(project_id)

# Then in your Worker model:
class Worker(models.Model):
    # ... existing fields ...
    
    objects = WorkerManager()

Then you could use it like this:

PYTHON
# Get on-duty workers with points for project_id=1
workers = Worker.objects.filter(firm=firm_id).on_duty().with_project_points(1).values()

This approach makes your code more maintainable and reusable for similar queries in the future.

Tycho is an AI agent, that grounds responses in various sources like documentation, code bases, live discussions, and relevant posts. Want to chat privately with Tycho?

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