我的自定义模型字段有什么问题? [英] What is wrong with my custom model field?
问题描述
我尝试实现一个您可以为其分配字符串的图像字段,它将自动从该URL获取图像.之后读取它,它将保存本地副本的路径.因此,我继承了Django的 ImageField
及其描述符类.
I try to implement an image field that you can assign a string to and it will automatically fetch the image from that URL. Reading it afterwards, it will hold the path to the local copy. Therefore, I inherited from Django's ImageField
and its descriptor class.
import uuid
import urllib.request
from django.core.files.base import ContentFile
from django.db import models
from django.db.models.fields.files import ImageFileDescriptor, ImageFieldFile
class UrlImageFileDescriptor(ImageFileDescriptor):
def __init__(self, field):
super().__init__(field)
def __get__(self, instance, owner=None):
# Get path to local copy on the server
try:
file = super().__get__(instance)
print('Get path to local copy', file.url)
return file.url if file else None
except:
return None
def __set__(self, instance, value):
# Set external URL to fetch new image from
print('Set image from URL', value)
# Validations
if not value:
return
value = value.strip()
if len(value) < 1:
return
if value == self.__get__(instance):
return
# Fetch and store image
try:
response = urllib.request.urlopen(value)
file = response.read()
name = str(uuid.uuid4()) + '.png'
content = ContentFile(file, name)
super().__set__(instance, content)
except:
pass
class UrlImageField(models.ImageField):
descriptor_class = UrlImageFileDescriptor
保存使用此字段的模型时,Django代码会引发错误'str'对象没有属性'_committed'
.这是Django 1.7c1中的相关代码.它位于db/models/fields/files.py中.该异常发生在if语句的行上.
When saving the model that uses this field, Django code raises an error 'str' object has no attribute '_committed'
. This is the related code from Django 1.7c1. It lives in db/models/fields/files.py. The exception occurs on the line of the if statement.
def pre_save(self, model_instance, add):
"Returns field's value just before saving."
file = super(FileField, self).pre_save(model_instance, add)
if file and not file._committed:
# Commit the file to storage prior to saving the model
file.save(file.name, file, save=False)
return file
我不明白 file
在这里是字符串.我唯一能想到的是描述符类 __ get __
返回字符串.但是,它使用 ContentFile
调用其基类的 __ get __
,因此应将其存储在模型的 __ dict __
中.谁可以给我解释一下这个?如何找到解决方法?
I don't understand file
being a string here. The only thing I can think of is that the descriptor classes __get__
returns string. However, it calls the __get__
of its base class with a ContentFile
, so that should be stored in the __dict__
of the model. Can someone explain this to me? How can I find a workaround?
推荐答案
问题是您需要返回一个 FieldFile
,以便您可以在Django的源代码中访问它的属性代码,您可以找到名为 FileDescriptor 这是 ImageFileDescriptor的父项,如果您在名称下查看 FileDescriptor
类,则可以找到该类的文档,并显示:
The problem is that you need to return a FieldFile
, so that way you can access to the properties of it, in django's source code you can find a class named FileDescriptor this is the parent of ImageFileDescriptor, if you look at the FileDescriptor
class under the name you can find the doc of the class and it says:
"""
The descriptor for the file attribute on the model instance. Returns a
FieldFile when accessed so you can do stuff like::
>>> from myapp.models import MyModel
>>> instance = MyModel.objects.get(pk=1)
>>> instance.file.size
Assigns a file object on assignment so you can do::
>>> with open('/tmp/hello.world', 'r') as f:
... instance.file = File(f)
"""
因此,您需要返回一个 FieldFile
而不是一个 String
,只需更改它的返回值即可.
So you need to return a FieldFile
not a String
just do it changing the return for this.
return None or file
更新:
我发现了您的问题,此代码对我有用:
I figured out your problem and this code works for me:
import uuid
import requests
from django.core.files.base import ContentFile
from django.db import models
from django.db.models.fields.files import ImageFileDescriptor, ImageFieldFile
class UrlImageFileDescriptor(ImageFileDescriptor):
def __init__(self, field):
super(UrlImageFileDescriptor, self).__init__(field)
def __set__(self, instance, value):
if not value:
return
if isinstance(value, str):
value = value.strip()
if len(value) < 1:
return
if value == self.__get__(instance):
return
# Fetch and store image
try:
response = requests.get(value, stream=True)
_file = ""
for chunk in response.iter_content():
_file+=chunk
headers = response.headers
if 'content_type' in headers:
content_type = "." + headers['content_type'].split('/')[1]
else:
content_type = "." + value.split('.')[-1]
name = str(uuid.uuid4()) + content_type
value = ContentFile(_file, name)
except Exception as e:
print e
pass
super(UrlImageFileDescriptor,self).__set__(instance, value)
class UrlImageField(models.ImageField):
descriptor_class = UrlImageFileDescriptor
class TryField(models.Model):
logo = UrlImageField(upload_to="victor")
custom_field = TryField.objects.create(logo="url_iof_image or File Instance") will work!!
这篇关于我的自定义模型字段有什么问题?的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!