Python Django - 模型字段的 ForeignKey 类选择

Question

我想这样做，以便在创建和实例化模型时可以为字段模型/类选择外键。所以是这样的：

class Posts(models.Model):

    OwnerType = (
        (Accounts, 'User'),
        (Groups, 'Group'),
    )

    PostTypes = (
        ('Text', 'Text'),
        ('Photo', 'Photo'),
        ('Audio', 'Audio'),
        ('Video', 'Video'),
        ('Link', 'Link'),
    )

    owner = models.ForeignKey(OwnerType, default = 0, related_name = "post_owner")
    ownerid = models.IntegerField(blank = False, default = 0)
    owner_type = models.CharField(blank = False, default = '', max_length = 50)

    title = models.CharField(max_length = 500, default = '')
    contents = models.CharField(max_length = 500, default = '')
    attachment = models.CharField(max_length = 500, default = '')
    attachment_type = models.CharField(max_length = 500, default = '')
    link = models.CharField(max_length = 500, default = '')

    post_type = models.CharField(max_length = 20, choices = PostTypes, default = '')
    status = models.CharField(max_length = 20, default = 'public') # either public, private, or deleted

    date_created = models.DateField(auto_now_add=True)
    last_active = models.DateField(auto_now=True)

    @property
    def serialize(self):
        return {
            'p_id': self.id,

            'ownerid': self.ownerid,
            'owner': self.owner.serialize,
            'owner_type': self.owner_type,
            'title': self.title,
            'contents': self.contents,
            'attachment': self.attachment,
            'attachment_type': self.attachment_type,
            'link': self.link,
            'post_type': self.post_type,
            'status': self.status,
            'date_created': self.date_created,
            'last_active': self.last_active
        }

    class Meta:
        db_table = "posts"

# ---

然后我得到这个错误：

    Traceback (most recent call last):
  File "manage.py", line 9, in <module>
    execute_from_command_line(sys.argv)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/core/management/__init__.py", line 353, in execute_from_command_line
    utility.execute()
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/core/management/__init__.py", line 327, in execute
    django.setup()
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/__init__.py", line 18, in setup
    apps.populate(settings.INSTALLED_APPS)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/apps/registry.py", line 108, in populate
    app_config.import_models(all_models)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/apps/config.py", line 202, in import_models
    self.models_module = import_module(models_module_name)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/importlib/__init__.py", line 37, in import_module
    __import__(name)
  File "/Users/RyanWaite/Desktop/epsity/webapp/models.py", line 320, in <module>
    class Posts(models.Model):
  File "/Users/RyanWaite/Desktop/epsity/webapp/models.py", line 335, in Posts
    owner = models.ForeignKey(OwnerType, default = 0, related_name = "post_owner")
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/db/models/fields/related.py", line 754, in __init__
    RECURSIVE_RELATIONSHIP_CONSTANT,
AssertionError: ForeignKey(((<class 'webapp.models.Accounts'>, u'User'), (<class 'webapp.models.Groups'>, u'Group'))) is invalid. First parameter to ForeignKey must be either a model, a model name, or the string u'self'

这可能吗？创建模型的新实例时，我可以为外键选择模型吗？我有两种可以发帖的模型：用户和组。用户可以发帖，或者群组可以发帖。

Answer 1

所以这是我的自定义方法：

我添加了 type 和 type_id 字段，其中 type 是 Model Class 的字符串。 然后我创建了一个函数，它将根据给定的参数返回模型实例。例如。 ：

def returnModelSerialized(type, id):
    if id == None:
        return 'error --- Missing id'

    if type == '' or Type == None:
        return 'error --- invalid type'

    if type == 'Account':
        obj = Accounts.objects.get(id = id)
        return obj.serialize

    if type == 'Group':
        obj = Groups.objects.get(id = id)
        return obj.serialize

所以当我调用一个序列化属性方法时，它看起来像这样：

class Likes(models.Model):

OwnerType = (
    ('Account', 'Account'),
    ('Group', 'Group'),
)

ContentType = (
    ('Post', 'Post'),
    ('Comment', 'Comment'),
    ('Reply', 'Reply'),
    ('Group', 'Group'),
    ('Event', 'Event'),
)

ownerid = models.IntegerField(blank = False, default = 0)
owner_type = models.CharField(choices = OwnerType, blank = False, default = '', max_length = 50)

item_type = models.CharField(choices = ContentType, blank = False, default = '', max_length = 50)
item_id = models.IntegerField(blank = False, default = 0)

date_created = models.DateField(auto_now_add=True)
last_active = models.DateField(auto_now=True)

@property
def serialize(self):
    return {
        'like_id': self.id,

        'ownerid': self.ownerid,
        'owner': returnModelSerialized( self.owner_type , self.ownerid ),
        'owner_type': self.owner_type,
        'item_type': self.item_type.serialize,
        'item_id': self.item_id,
        'date_created': self.date_created,
        'last_active': self.last_active
    }

class Meta:
    db_table = "likes"

Answer 2

来自文档doc

普通的 ForeignKey 只能“指向”另一个模型，这意味着如果 TaggedItem 模型使用 ForeignKey，则必须选择一个且只有一个模型来存储标签

您可以使用GenericForeignKey，它允许与任何模型建立关系