How can I resolve Django reverse accessor clashes for multiple ForeignKey fields in my task management models?

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I am developing a Django task management app where I need to create two models: one for planned tasks (PlanTask) and one for actual tasks (ActualTask).

The PlanTask model includes fields like Task Area, Task Type, Task Assigned Date, Assigned to, and Supporting member. The ActualTask model references PlanTask and calculates various progress metrics (planning, field work, reporting, and approval progress) based on several DecimalFields and date fields. The models are defined as follows:

PYTHON
class PlanTask(models.Model):
       id = models.AutoField(primary_key=True)
       task_area = models.CharField(max_length=255, null=False)
       task_type = models.CharField(max_length=255, null=False)
       task_assigned_date = models.DateField(null=False)
       assigned_to = models.ForeignKey(User, null=True, blank=True, on_delete=models.DO_NOTHING)
       supporting_member = models.ForeignKey(User, null=True, blank=True, on_delete=models.DO_NOTHING)

       planned_start_date = models.DateField(null=True, blank=True)
       planned_planning_start = models.DateField(null=True, blank=True)
       planned_planning_end = models.DateField(null=True, blank=True)
       planned_field_work_start = models.DateField(null=True, blank=True)
       planned_field_work_end = models.DateField(null=True, blank=True)
       planned_reporting_start = models.DateField(null=True, blank=True)
       planned_reporting_end = models.DateField(null=True, blank=True)
       planned_approval_start = models.DateField(null=True, blank=True)
       planned_approval_end = models.DateField(null=True, blank=True)
       planned_end_date = models.DateField(null=True, blank=True)

This is the ActualTask model:

PYTHON
class ActualTask(models.Model):
    id = models.AutoField(primary_key=True)
    task_area = models.ForeignKey(PlanTask, null=True, blank=True, on_delete=models.CASCADE)  # Updated to correct model
    STATUS_CHOICES = [
        ('Assigned', 'Assigned'),
        ('WIP', 'WIP'),
        ('Completed', 'Completed'),
    ]
    status = models.CharField(max_length=50, choices=STATUS_CHOICES, default='Assigned', null=False)

    planning_stage = models.CharField(max_length=255, null=True, blank=True)
    research_planning = models.DecimalField(max_digits=5, decimal_places=2,
                                            choices=[(0, '0'), (10, '10'), (20, '20'), (25, '25')],
                                            validators=[MaxValueValidator(25)], null=True, blank=True)
    task_plan = models.DecimalField(max_digits=5, decimal_places=2,
                                     choices=[(0, '0'), (10, '10'), (20, '20'), (25, '25')],
                                     validators=[MaxValueValidator(25)], null=True, blank=True)
    initial_task_meeting = models.DecimalField(max_digits=5, decimal_places=2,
                                                choices=[(0, '0'), (10, '10'), (20, '20'), (25, '25')],
                                                validators=[MaxValueValidator(25)], null=True, blank=True)
    process_walkover = models.DecimalField(max_digits=5, decimal_places=2,
                                           choices=[(0, '0'), (10, '10'), (20, '20'), (25, '25')],
                                           validators=[MaxValueValidator(25)], null=True, blank=True)

    @property
    def planning_progress(self):
        return (self.research_planning or 0) + (self.task_plan or 0) + (self.initial_task_meeting or 0) + (
                    self.process_walkover or 0)

    field_work_stage = models.CharField(max_length=255, null=True, blank=True)
    documents_verification = models.DecimalField(max_digits=5, decimal_places=2,
                                                 choices=[(0, '0'), (10, '10'), (20, '20'), (25, '25')],
                                                 validators=[MaxValueValidator(25)], null=True, blank=True)
    research_work_data_analysis = models.DecimalField(max_digits=5, decimal_places=2,
                                                      choices=[(0, '0'), (10, '10'), (20, '20'), (25, '25')],
                                                      validators=[MaxValueValidator(25)], null=True, blank=True)
    research_work_field = models.DecimalField(max_digits=5, decimal_places=2,
                                              choices=[(0, '0'), (10, '10'), (20, '20'), (25, '25')],
                                              validators=[MaxValueValidator(25)], null=True, blank=True)
    query_clarification = models.DecimalField(max_digits=5, decimal_places=2,
                                              choices=[(0, '0'), (10, '10'), (20, '20'), (25, '25')],
                                              validators=[MaxValueValidator(25)], null=True, blank=True)

    @property
    def field_work_progress(self):
        return (self.documents_verification or 0) + (self.research_work_data_analysis or 0) + (
                    self.research_work_field or 0) + (self.query_clarification or 0)

    reporting_stage = models.CharField(max_length=255, null=True, blank=True)
    drafting_report = models.DecimalField(max_digits=5, decimal_places=2,
                                          choices=[(0, '0'), (10, '10'), (20, '20'), (25, '25')],
                                          validators=[MaxValueValidator(25)], null=True, blank=True)
    task_presentation = models.DecimalField(max_digits=5, decimal_places=2,
                                             choices=[(0, '0'), (10, '10'), (20, '20'), (25, '25')],
                                             validators=[MaxValueValidator(25)], null=True, blank=True)
    taskee_feedback_pending = models.DecimalField(max_digits=5, decimal_places=2,
                                                   choices=[(0, '0'), (10, '10'), (20, '20'), (25, '25')],
                                                   validators=[MaxValueValidator(25)], null=True, blank=True)
    final_presentation = models.DecimalField(max_digits=5, decimal_places=2,
                                             choices=[(0, '0'), (10, '10'), (20, '20'), (25, '25')],
                                             validators=[MaxValueValidator(25)], null=True, blank=True)

    @property
    def reporting_progress(self):
        return (self.drafting_report or 0) + (self.task_presentation or 0) + (self.taskee_feedback_pending or 0) + (
                    self.final_presentation or 0)

    approval_stage = models.CharField(max_length=255, null=True, blank=True)
    mgmt_approval = models.DecimalField(max_digits=5, decimal_places=2,
                                        choices=[(0, '0'), (10, '10'), (20, '20'), (25, '25')],
                                        validators=[MaxValueValidator(25)], null=True, blank=True)
    ic_to_taskee = models.DecimalField(max_digits=5, decimal_places=2,
                                        choices=[(0, '0'), (10, '10'), (20, '20'), (25, '25')],
                                        validators=[MaxValueValidator(25)], null=True, blank=True)
    gr_to_taskee = models.DecimalField(max_digits=5, decimal_places=2,
                                        choices=[(0, '0'), (10, '10'), (20, '20'), (25, '25')],
                                        validators=[MaxValueValidator(25)], null=True, blank=True)
    completed = models.DecimalField(max_digits=5, decimal_places=2,
                                    choices=[(0, '0'), (10, '10'), (20, '20'), (25, '25')],
                                    validators=[MaxValueValidator(25)], null=True, blank=True)

    @property
    def approval_progress(self):
        return (self.mgmt_approval or 0) + (self.ic_to_taskee or 0) + (self.gr_to_taskee or 0) + (self.completed or 0)

    @property
    def overall_progress(self):
        return (self.planning_progress * 0.15) + (self.field_work_progress * 0.5) + (self.reporting_progress * 0.25) + (
                    self.approval_progress * 0.1)

    actual_start_date = models.DateField(null=True, blank=True)
    actual_planning_start = models.DateField(null=True, blank=True)
    actual_planning_end = models.DateField(null=True, blank=True)
    delay_planning = models.IntegerField(default=0)
    actual_field_work_start = models.DateField(null=True, blank=True)
    actual_field_work_end = models.DateField(null=True, blank=True)
    delay_field_work = models.IntegerField(default=0)
    actual_reporting_start = models.DateField(null=True, blank=True)
    actual_reporting_end = models.DateField(null=True, blank=True)
    delay_reporting = models.IntegerField(default=0)
    actual_approval_start = models.DateField(null=True, blank=True)
    actual_approval_end = models.DateField(null=True, blank=True)
    delay_approval = models.IntegerField(default=0)
    actual_end_date = models.DateField(null=True, blank=True)
    delay = models.IntegerField(default=0)

    def save(self, *args, **kwargs):
        # Update actual dates and delays
        if self.status == 'WIP' and not self.actual_start_date:
            self.actual_start_date = timezone.now().date()
        if self.planning_progress > 0 and not self.actual_planning_start:
            self.actual_planning_start = timezone.now().date()
        if self.planning_progress == 100 and not self.actual_planning_end:
            self.actual_planning_end = timezone.now().date()
        if self.field_work_progress > 0 and not self.actual_field_work_start:
            self.actual_field_work_start = timezone.now().date()
        if self.field_work_progress == 100 and not self.actual_field_work_end:
            self.actual_field_work_end = timezone.now().date()
        if self.reporting_progress > 0 and not self.actual_reporting_start:
            self.actual_reporting_start = timezone.now().date()
        if self.reporting_progress == 100 and not self.actual_reporting_end:
            self.actual_reporting_end = timezone.now().date()
        if self.approval_progress > 0 and not self.actual_approval_start:
            self.actual_approval_start = timezone.now().date()
        if self.approval_progress == 100 and not self.actual_approval_end:
            self.actual_approval_end = timezone.now().date()
        if self.status == 'Completed' and not self.actual_end_date:
            self.actual_end_date = timezone.now().date()

        # Calculate delays
        # Assuming planned_* fields are provided and should be datetime.date objects
        today = timezone.now().date()
        if hasattr(self, 'planned_planning_end') and self.planned_planning_end:
            self.delay_planning = max((today - self.planned_planning_end).days,
                                      0) if self.actual_planning_end is None else max(
                (self.actual_planning_end - self.planned_planning_end).days, 0)
        if hasattr(self, 'planned_field_work_end') and self.planned_field_work_end:
            self.delay_field_work = max((today - self.planned_field_work_end).days,
                                        0) if self.actual_field_work_end is None else max(
                (self.actual_field_work_end - self.planned_field_work_end).days, 0)
        if hasattr(self, 'planned_reporting_end') and self.planned_reporting_end:
            self.delay_reporting = max((today - self.planned_reporting_end).days,
                                       0) if self.actual_reporting_end is None else max(
                (self.actual_reporting_end - self.planned_reporting_end).days, 0)
        if hasattr(self, 'planned_approval_end') and self.planned_approval_end:
            self.delay_approval = max((today - self.planned_approval_end).days,
                                      0) if self.actual_approval_end is None else max(
                (self.actual_approval_end - self.planned_approval_end).days, 0)

        self.delay = self.delay_planning + self.delay_field_work + self.delay_reporting + self.delay_approval

        super().save(*args, **kwargs)

    def __str__(self):
        return f"task {self.id}: {self.task_area}"

My intention is to have team leaders assign tasks which then appear on the assigned list for particular team members. Team members can move a task to their work-in-progress list and later to a completed list once done. Additionally, I plan to archive the tasks when the year concludes. The PlanTask model acts as a reference for tracking progress and delays in the ActualTask model.

However, using two ForeignKey fields (assigned_to and supporting_member) that both reference the User model produces the following error:

Reverse accessor ‘User.plan_set’ for ‘task_management.PlanTask.assigned_to’ clashes with reverse accessor for ‘task_management.PlanTask.supporting_member’
HINT: Add or change a related_name argument to the definition.

Is it possible to link the PlanTask and ActualTask models in this way? What is the best approach to resolve this reverse accessor clash when using multiple ForeignKey fields to the same model?

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Answers 1

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1 Answer

Answer by StackOverflow TychoAI Agent • 9 days ago

Resolving Multiple Foreign Keys to the Same Model in Django

You're encountering a common issue when using multiple foreign keys to the same model in Django. The error occurs because Django automatically creates reverse relations from the referenced model back to your model, and when you have multiple foreign keys to the same model, these reverse relations clash.

Solution: Add `related_name` to Foreign Keys

To resolve this issue, you need to add a unique related_name attribute to each foreign key that points to the same model. This will create distinct reverse accessors and prevent the clash.

Here's how to modify your PlanTask model:

PYTHON
class PlanTask(models.Model):
    id = models.AutoField(primary_key=True)
    task_area = models.CharField(max_length=255, null=False)
    task_type = models.CharField(max_length=255, null=False)
    task_assigned_date = models.DateField(null=False)
    assigned_to = models.ForeignKey(
        User, 
        related_name='assigned_tasks',  # Add this
        null=True, 
        blank=True, 
        on_delete=models.DO_NOTHING
    )
    supporting_member = models.ForeignKey(
        User, 
        related_name='supporting_tasks',  # Add this
        null=True, 
        blank=True, 
        on_delete=models.DO_NOTHING
    )
    
    # Rest of your model remains the same

Similarly, for the ActualTask model, you should add a related_name to the foreign key referencing PlanTask:

PYTHON
class ActualTask(models.Model):
    id = models.AutoField(primary_key=True)
    task_area = models.ForeignKey(
        PlanTask, 
        related_name='actual_tasks',  # Add this
        null=True, 
        blank=True, 
        on_delete=models.CASCADE
    )
    # Rest of your model remains the same

How This Works

With these changes:

You can access tasks assigned to a user with: user.assigned_tasks.all()
You can access tasks where a user is a supporting member with: user.supporting_tasks.all()
You can access actual tasks related to a plan task with: plan_task.actual_tasks.all()

This approach is exactly what Django recommends when you have multiple foreign keys to the same model, as shown in the documentation example with the Friendship model that has two foreign keys to the Person model.

Additional Considerations

Field Name in ActualTask: Your task_area field in ActualTask is a foreign key to PlanTask, but the name might be confusing since it suggests it's related to the task area rather than the entire plan task. Consider renaming it to plan_task for clarity.
Admin Interface: If you're using Django's admin interface, you might want to set up inline forms for the related models. For example:

PYTHON
from django.contrib import admin
from .models import PlanTask, ActualTask

class ActualTaskInline(admin.TabularInline):
    model = ActualTask
    fk_name = "task_area"  # or whatever you rename it to

class PlanTaskAdmin(admin.ModelAdmin):
    inlines = [ActualTaskInline]

admin.site.register(PlanTask, PlanTaskAdmin)
admin.site.register(ActualTask)

This approach will allow you to manage your models effectively while maintaining the relationships between them.

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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