如何在 django 模型中动态创建属性方法？

Question

I am creating property methods for every model where the model attribute includes ImageField or FileField. So, I decided to make an abstract model where I check the fields in the model and if there are any ImageField and FileField in the model the property method creates it automatically by itself.

I usually add '_url' to the attribute when I create the method

Below is what I do usually

class MyModel(models.Model):
    image = ImageField(...)
    file = FileField(...)
    ...

    @property
    def image_url(self):
        if self.image and hasattr(self.image, 'url'):
            return self.image.url


    @property
    def file_url(self):
        if self.file and hasattr(self.file, 'url'):
            return self.file.url

    ...

Below what I did so far

class MyModel(models.Model):
    ...
    

    def __new__(cls, value):
        fields = self._meta.get_fields()
        for field in fields:
            if isinstance(field, ImageField) or isinstance(field, FileField):
                ???

Any suggestions?

Answer 1

Use mixins.

class ImageUrlMixin:

    @property
    def image_url(self):
        if self.image and hasattr(self.image, "url"):
            return self.image.url

class FileUrlMixin:

    @property
    def file_url(self):
        if self.file and hasattr(self.file, "url"):
            return self.file.url

class FileImageUrlMixin(FileUrlMixin, ImageUrlMixin):
    pass

class OnlyHasFileFieldModel(FileUrlMixin, models.Model):
    # ..model implementation

class OnlyHasImageFieldModel(ImageUrlMixin, models.Model):
    # ..model implementation

class HasBothFileAndImageFieldModel(FileImageUrlMixin, models.Model):
    # ..model implementation

Or if you want to support fields dynamically eg my_model.arbitrary_field_url :

class DynamicFieldUrlMixin:

    def __getattr__(self, name):
        if name.endswith("_url"):
            field_name = "".join(name.split("_")[:-1])
            field = getattr(self, field_name, None)
            if hasattr(field, "url"):
                return field.url
        raise AttributeError