FileField / ImageField 迁移不适用

Question

如果有人能帮助我解决这个 Django 错误，我将不胜感激，我的模型是这样创建的：

from django.db import models
from django.utils.timezone import now

# Create your models here.


class Album(models.Model):
    album_title = models.CharField(max_length=200)
    creation_date = models.DateTimeField(default=now)

    def __str__(self):
        return self.album_title


class Photo(models.Model):
    name = models.CharField(max_length=300, default="")
    album = models.ForeignKey(Album, on_delete=models.CASCADE)
    # file = models.ImageField(upload_to=Album.album_title, null=True, blank=True)
    description = models.CharField(max_length=1000, default="")
    file_url = models.CharField(max_length=1000)
    selected = models.BooleanField(default=False)
    date_uploaded = models.DateTimeField(default=now)
    file_type = models.Choices('Raw', 'JPEG')

    def __str__(self):
        return str(self.album) + "ID.{:0>3}".format(self.id)

如果我像这样进行迁移，一切正常，但是每当我取消注释该行时：

file = models.ImageField(upload_to=Album.album_title, null=True, blank=True) 在我的班级照片中，我无法进行迁移。

当我运行 python3 manage.py make migrations 代码时，我有这个堆栈跟踪：

Traceback (most recent call last):
  File "/Users/adamspierredavid/Documents/django/crueltouch/manage.py", line 22, in <module>
    main()
  File "/Users/adamspierredavid/Documents/django/crueltouch/manage.py", line 18, in main
    execute_from_command_line(sys.argv)
  File "/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/site-packages/django/core/management/__init__.py", line 419, in execute_from_command_line
    utility.execute()
  File "/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/site-packages/django/core/management/__init__.py", line 413, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/site-packages/django/core/management/base.py", line 354, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/site-packages/django/core/management/base.py", line 398, in execute
    output = self.handle(*args, **options)
  File "/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/site-packages/django/core/management/base.py", line 89, in wrapped
    res = handle_func(*args, **kwargs)
  File "/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/site-packages/django/core/management/commands/makemigrations.py", line 190, in handle
    self.write_migration_files(changes)
  File "/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/site-packages/django/core/management/commands/makemigrations.py", line 227, in write_migration_files
    migration_string = writer.as_string()
  File "/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/site-packages/django/db/migrations/writer.py", line 141, in as_string
    operation_string, operation_imports = OperationWriter(operation).serialize()
  File "/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/site-packages/django/db/migrations/writer.py", line 99, in serialize
    _write(arg_name, arg_value)
  File "/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/site-packages/django/db/migrations/writer.py", line 63, in _write
    arg_string, arg_imports = MigrationWriter.serialize(_arg_value)
  File "/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/site-packages/django/db/migrations/writer.py", line 271, in serialize
    return serializer_factory(value).serialize()
  File "/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/site-packages/django/db/migrations/serializer.py", line 201, in serialize
    return self.serialize_deconstructed(path, args, kwargs)
  File "/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/site-packages/django/db/migrations/serializer.py", line 88, in serialize_deconstructed
    arg_string, arg_imports = serializer_factory(arg).serialize()
  File "/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/site-packages/django/db/migrations/serializer.py", line 353, in serializer_factory
    raise ValueError(
ValueError: Cannot serialize: <django.db.models.query_utils.DeferredAttribute object at 0x10a1bcfd0>
There are some values Django cannot serialize into migration files.
For more, see https://docs.djangoproject.com/en/3.2/topics/migrations/#migration-serializing

我去了这个链接https://docs.djangoproject.com/en/3.2/topics/migrations/#migration-serializing 看看它说什么，但我找不到可以理解的东西（在我的水平上）来解决这个问题。问题是在之前的项目中，当我想添加图像时，Django 要求我安装 Pillow，在我安装之后，我的代码就可以工作了。我可以进行迁移，但现在什么都没有。我使用 Postgres 作为我的数据库。

谢谢你们的帮助。 （P.S：我是学习Django的初学者）

Answer 1

这里的问题是ImageField，它有字段upload_to，它应该是一个路径名，它不能指向一个尚未创建实例的类Album。如果您的Photo 应该基于album 字段保存，我想看到 代码行file = models.ImageField(upload_to=Album.album_title, null=True, blank=True)和行album = models.ForeignKey(Album, on_delete=models.CASCADE)，我在这里考虑，你想根据你指向的album保存file。

你可以试试这样的

def get_path(instance, filename):
    return '{0}/{1}'.format(instance.file.album_title, filename)

你的file 行代码应该是这样的

file = models.ImageField(upload_to=get_path, null=True, blank=True)

---

您在这里所做的是，您定义了一个函数，以确保您的路径是根据您的输入动态设置的。在get_upload_path函数内部，你可以随意改变路径结构。

有关更多见解，您可以参考此文档 https://docs.djangoproject.com/en/3.2/ref/models/fields/#django.db.models.FileField.upload_to

Imagefield 继承自 django 模型中的 FileField，所以这个文档就足够了。