Django Model Relationships for Problem and Responsibility Models

Based on your described model structure, I'll provide guidance on how to properly set up your relationships.

Problem Model Structure

For your Problem model, it's sufficient to have just a foreign key to Responsibility along with any additional fields specific to the Problem. You don't need to duplicate all the foreign keys that are already in the Responsibility model.

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from django.db import models

class Problem(models.Model):
    responsibility = models.ForeignKey(
        'Responsibility', 
        on_delete=models.CASCADE,
        related_name='problems'
    )
    title = models.CharField(max_length=200)
    description = models.TextField()
    # Other Problem-specific fields

Responsibility Model Structure

For your Responsibility model, since System already has a foreign key to Project, you technically don't need to include Project directly in the Responsibility model. However, including it depends on your specific use case:

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from django.db import models

class Responsibility(models.Model):
    system = models.ForeignKey('System', on_delete=models.CASCADE)
    department = models.ForeignKey('Department', on_delete=models.CASCADE)
    employee = models.ForeignKey('Employee', on_delete=models.CASCADE)
    # You can include project if you need direct access, but it's not strictly necessary
    # project = models.ForeignKey('Project', on_delete=models.CASCADE)
    # Other Responsibility-specific fields

Filtering Problems by Project

To filter problems for a given project in your template, you can use Django's ability to traverse relationships. Even without a direct foreign key from Problem to Project, you can still filter using:

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# In your view
problems = Problem.objects.filter(responsibility__system__project=project_id)

This query will find all problems associated with responsibilities that are linked to systems belonging to the specified project.

Recommendation

1. Keep your model structure clean by avoiding redundant foreign keys
2. Use Django's relationship traversal capabilities for filtering
3. Only add direct foreign keys when you need to optimize specific queries that are frequently used

This approach maintains data integrity while giving you the flexibility to query your data in various ways.