82 lines
3.6 KiB
Plaintext
82 lines
3.6 KiB
Plaintext
user: when both tare and gross are filled out, net should be calculated and saved (at backend). doc_number should be generated and assigned to the vehicle record. how will be the document number generated, what is better, use the vehicle id or a generator?
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Claude’s Plan
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Plan: Auto-calculate net + assign doc_number when both tare and gross are set
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Context
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One vehicle record = one weighing trip. When both tare and gross are recorded, the backend should
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automatically compute net = gross - tare, stamp net_date/net_user, and assign a unique
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document number formatted as YYYY-NNNNNN (year + 6-digit sequential counter, resetting per year).
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No frontend change is needed — the net and doc_number come back in the existing SSE broadcast.
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Files to Modify
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File Change
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backend/api/models.py Add DocumentCounter model
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backend/vehicles/models.py Add doc_number field to Vehicle
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backend/api/serializers.py Add net, net_date, net_user_name, doc_number to VehicleSerializer
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backend/api/views.py Update set_tare and set_gross to compute net + doc_number
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new migration in api For DocumentCounter
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new migration in vehicles For doc_number on Vehicle
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Step 1 — Add DocumentCounter model (backend/api/models.py)
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class DocumentCounter(models.Model):
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year = models.IntegerField(unique=True)
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last_number = models.IntegerField(default=0)
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Add a helper function in the same file (or in views.py, but models.py keeps it reusable):
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from django.db import transaction
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def generate_doc_number(year):
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with transaction.atomic():
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counter, _ = DocumentCounter.objects.select_for_update().get_or_create(
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year=year, defaults={'last_number': 0}
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)
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counter.last_number += 1
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counter.save()
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return f"{year}-{counter.last_number:06d}"
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Step 2 — Add doc_number to Vehicle (backend/vehicles/models.py)
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doc_number = models.CharField(max_length=20, null=True, blank=True, unique=True)
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Place after the net_user field.
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Step 3 — Update VehicleSerializer (backend/api/serializers.py)
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Add to the VehicleSerializer:
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net_user_name = serializers.CharField(source='net_user.username', read_only=True, default=None)
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Add to fields list:
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'net', 'net_date', 'net_user', 'net_user_name', 'doc_number'
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Add to read_only_fields:
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'net', 'net_date', 'net_user', 'net_user_name', 'doc_number'
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Step 4 — Update set_tare and set_gross (backend/api/views.py)
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Extract a helper to avoid duplication:
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def _maybe_finalize(vehicle, user):
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"""If both tare and gross are now set, compute net and assign doc_number."""
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if vehicle.tare is not None and vehicle.gross is not None and vehicle.net is None:
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vehicle.net = vehicle.gross - vehicle.tare
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vehicle.net_date = timezone.now()
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vehicle.net_user = user
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vehicle.doc_number = generate_doc_number(timezone.now().year)
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vehicle.save()
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Call _maybe_finalize(vehicle, request.user) at the end of both set_tare and set_gross,
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before the SSE broadcast and serializer response (so the response already contains net + doc_number).
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Import generate_doc_number from api.models.
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Step 5 — Migrations
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python manage.py makemigrations api # DocumentCounter
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python manage.py makemigrations vehicles # doc_number on Vehicle
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python manage.py migrate
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Verification
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Create a vehicle with no tare/gross → net and doc_number are null
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Set tare → net still null (only one weight set)
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Set gross → net is calculated, net_date and net_user are set, doc_number is "2026-000001"
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Second vehicle completes → doc_number is "2026-000002"
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Race condition test (optional): two simultaneous requests → both get unique sequential numbers
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Frontend SSE update reflects net and doc_number automatically (no frontend change needed) |