React / Django App：需要在使用序列化程序保存之前更新放置路由中的字段，在后端使用自定义函数

Question

I'm trying to change the content of a field with my own function. I'm using a simplified function that adds commas between each word. I want to be able to send my comma-fied sentence to the frontend but I don't know how to do that with the serializer that was given in Django documentation. I can't find any examples online of someone trying to do this online. I also need to do this in the backend because some of my other custom functions need access to a specific python library.

Here is my api > views.py

@api_view(['PUT'])
def accentLine(request, pk):
    data = request.data
    line = Lines.objects.get(id=pk)

    if data['accent'] == 'shatner':
        shatnerLine = line.content.replace(' ', ', ')
        line.translation = shatnerLine
        line.save()

    serializer = LineSerializer(instance=line, data=data)

    if serializer.is_valid():
        serializer.save()

    return Response(serializer.data)

Here is my api > models.py

class Lines(models.Model):
    # userId = models.ForeignKey(Users, on_delete=models.CASCADE)
    script = models.ForeignKey(Scripts, null=True, on_delete=models.SET_NULL)
    title = models.CharField(max_length=50, null=True)
    content = models.TextField(max_length=5000, null=True)
    accent = models.CharField(max_length=50, default='english')
    translation = models.TextField(max_length=5000, null=True)
    updatedAt = models.DateField(auto_now=True)

Here is my api > serializers.py

from rest_framework.serializers import ModelSerializer
from .models import Lines

class LineSerializer(ModelSerializer):
    class Meta:
        model = Lines
        fields = '__all__'

Answer 1

First and foremost, you are calling save on the model instance twice by calling it directly on the instance, and then again on the serializer. The serializer save method will perform save on the model instance itself. Docs on saving instances with serializers: https://www.django-rest-framework.org/api-guide/serializers/#saving-instances

To achieve what you want to do you should create a custom serializer field probably called TranslationField and either override the to_internal_value method to perform your string mutations before the data is persisted to the database, or override to_representation which will perform the string mutations before the data is returned from the serializer. It depends on if you wish to persist the field... with commas or add the commas when getting the data via serializer. Docs on custom fields here: https://www.django-rest-framework.org/api-guide/fields/#custom-fields

Once you set up your custom field you will not perform any mutations in your accentLine view and instead simply pass the request data to the serializer like so

@api_view(['PUT'])
def accentLine(request, pk):
    data = request.data
    line = Lines.objects.get(id=pk)

    serializer = LineSerializer(instance=line, data=data)

    if serializer.is_valid():
        serializer.save()

    return Response(serializer.data)