如何在Django REST框架中使字段在创建时可编辑并在更新时只读

Question

我想实现一种 Django 模型的常量字段。我希望在创建模型实例时设置该字段（通过 REST 框架 API），但在更新此字段时必须禁止更改。在 Django 本身或 REST 框架序列化程序选项中是否有一种优雅的方法？

Answer 1

覆盖序列化器中的更新方法并移除该字段：

class MySerializer(serializers.ModelSerializer):        
    def update(self, instance, validated_data):
        validated_data.pop('myfield', None)  # prevent myfield from being updated
        return super().update(instance, validated_data)

Answer 2

上述两种解决方案都有效，但创建可扩展方法来控制任何 CRUD 操作的修改权限的好方法如下：

1. 创建基本序列化程序类：BaseSerializer
2. 在所有序列化程序类中从此类继承

基本序列化程序类中的控件：

class BaseSerializer(DynamicFieldsSerializer):
    # This overrides a built-in base class method
    def get_extra_kwargs(self):
        """Add additional constraints between CRUD methods to
        any particular field

        NB: Use the same extra_kwags dict object in all method calls
        - important to make changes on central object
        """
        extra_kwargs_for_edit = super().get_extra_kwargs()
        
        # Example of making uuid only editable on create, not update 
        self.add_create_only_constraint_to_field("uuid", extra_kwargs_for_edit)
        return extra_kwargs_for_edit

    def add_create_only_constraint_to_field(self, key: str, extra_kwargs: dict) -> dict:
        """Ensures key is only writable on create, not update"""
        action = self.context["view"].action
        if action in ["create"]:
            kwargs = extra_kwargs.get(key, {})
            kwargs["read_only"] = False
            extra_kwargs[key] = kwargs
        elif action in ["update", "partial_update"]:
            kwargs = extra_kwargs.get(key, {})
            kwargs["read_only"] = True
            extra_kwargs[key] = kwargs

     # You could add other constraints to CRUD operations here
     # def another_field_constrained_by_crud_method(self, key: str, extra_kwargs: dict) -> dict:

class SomeModelSerializer(BaseSerializer):
    # Your serializer logic here
    pass

感谢Nicholas Coles的回答！