Question

我写了一个自定义django字段来规范化我们系统收到的URL。但是，该网址只会在重新加载后返回归一化的值。

from django.db import models

def _rewrite_internal_url(url):
    # 
    return 'http://www.google.com/1.jpg'

class NormalizedURLField(models.URLField):
    def to_python(self, value):
        value = super().to_python(value)
        return _rewrite_internal_url(value)


    def from_db_value(self, value, expression, connection):
        if value is None:
            return value

        return _rewrite_internal_url(value)

class DjangoTest(models.Model):
    url = NormalizedURLField()


instance = DjangoTest.objects.create(url="http://www.google.com/2.jpg")
print(instance.url) # still http://www.google.com/2.jpg
instance.referesh_from_db()
print(instance.url) # update to http://www.google.com/1.jpg

Answer 1

如果您没有在NormalizedURLField字段中保存非规范化的URL，则不需要覆盖to_python和from_db_value。保存时，改写pre_save来转换和更新模型实例上的值：

class NormalizedURLField(models.URLField):

    def pre_save(self, model_instance, add):
        attr = super().pre_save(model_instance, add)
        rewritten = _rewrite_internal_url(attr)
        # update the value on the model instance
        setattr(model_instance, self.attname, rewritten)
        # return the rewritten value
        return rewritten

如果从数据库中获取数据时，如果您已经在数据库中拥有要转换的非标准化值，那么您仍然需要像完成操作那样实现from_db_value。

规范化Django字段的值

1 个答案: