Django Task — Model & Service

Scenario

You need to create the Project model for a workspace-based project management app. Projects belong to a workspace. Each project has a status, optional dates, and supports soft delete. Business logic for creating and archiving projects must live in a ProjectService class — not in the view.

What to Build

1. The Project model in models.py
2. A custom manager that excludes soft-deleted records by default
3. A ProjectService class in services.py
4. A migration file
5. Unit tests for the model constraints and service methods

Requirements

Project Model Fields

Model Constraints

class Meta:
    ordering = ['-created_at']
    verbose_name = 'Project'
    verbose_name_plural = 'Projects'
    constraints = [
        # A workspace cannot have two active projects with the same name
        models.UniqueConstraint(
            fields=['workspace', 'name'],
            condition=models.Q(deleted_at__isnull=True),
            name='unique_active_project_name_per_workspace'
        ),
        # end_date must be after start_date
        models.CheckConstraint(
            check=(
                models.Q(end_date__isnull=True) |
                models.Q(start_date__isnull=True) |
                models.Q(end_date__gt=models.F('start_date'))
            ),
            name='project_end_date_after_start_date'
        ),
    ]

Custom Manager

class ProjectManager(models.Manager):
    def get_queryset(self):
        return super().get_queryset().filter(deleted_at__isnull=True)

class Project(models.Model):
    objects = ProjectManager()        # default: excludes soft-deleted
    all_objects = models.Manager()    # includes soft-deleted

ProjectService Methods

create_project(workspace, name, created_by, description='', start_date=None, end_date=None)

Rules:

• name cannot be blank or exceed 100 characters
• If both end_date and start_date are provided: end_date must be after start_date
• A project with the same name cannot already exist in the workspace (active projects only)
• On success: create the project AND create a default TaskList named "General" linked to it
• On duplicate name: raise ValidationError("A project with this name already exists in this workspace.")

archive_project(project, actor)

Rules:

• project.status must not already be 'archived'
• On success: set project.status = 'archived', save the project
• Write an entry to AuditLog: action='project.archived', entity_id=project.id, actor=actor
• Caller's role must be checked by the view/permission layer before calling this method

What You Should NOT Do

× Put create_project or archive_project logic in the model's save() method
× Put business logic in the view (no Project.objects.create() in a view)
× Call Project.objects.create() directly from inside a view
× Use fields = '__all__' in any ModelForm or Serializer for this model
× Raise a generic Exception — always raise ValidationError or a named custom exception
× Skip the CheckConstraint and UniqueConstraint — they protect data at the DB level
× Forget to create the default TaskList inside create_project

Checklist to Run

Before marking done, run the Django Model Checklist.

Done When

[ ] Project model has all 11 fields with correct types and options
[ ] ForeignKey relationships have correct on_delete and related_name
[ ] UniqueConstraint for active projects with same name per workspace
[ ] CheckConstraint for end_date > start_date
[ ] class Meta has ordering, verbose_name, verbose_name_plural, constraints
[ ] Custom manager excludes soft-deleted records by default; all_objects includes them
[ ] __str__ returns a useful human-readable string (e.g., "{workspace.name} / {name}")
[ ] Migration generated, reviewed, and committed
[ ] ProjectService.create_project: validates name, checks uniqueness, creates project + TaskList
[ ] ProjectService.archive_project: validates not already archived, updates status, writes audit log
[ ] Unit tests cover: valid create, duplicate name error, invalid date range, archive, double-archive error
[ ] All tests pass