from rest_framework import serializers
from .models import Vehicle

class VehicleSerializer(serializers.ModelSerializer):
    class Meta:
        model = Vehicle
        fields = ['id', 'vehicle_number', 'trailer1_number', 'trailer2_number', 'driver_pid', 'driver_name', 'tare', 'tare_date', 'tare_user', 'gross', 'gross_date', 'gross_user']

    def validate(self, attrs):
        """Require driver_name on creation only; existing vehicles may have it as NULL."""
        if self.instance is None and not attrs.get('driver_name'):
            raise serializers.ValidationError({'driver_name': 'This field is required.'})
        return attrs