使用外键定义抽象模型到另一个抽象模型

Question

我正在尝试构建两个名为 SurveyQuestionBase 和 SurveyResponseBase 的抽象类，它们将作为模板快速定义新的具体模型，以在我们的网站上实施特定调查。我遇到的问题是强制SurveyResponseBase 模型在具体化时应将ForeignKey 定义为SurveyQuestionBase 的具体模型。

Django 不允许我们将ForeignKeys 定义为抽象类，所以我不能，例如，这样做： question = models.ForeignKey(SurveyQuestionBase) 出于类似的原因，我也不能将其命名为 None 或 app_label.ModelName。

一个 hacky 解决方法是创建一个新的具体模型 SurveyQuestionConcrete 并让 ForeignKey 指向此：question = models.ForeignKey(concrete_model)，并结合验证以确保替换此模型。

有没有更简洁的方法来实现同样的目标？ 我需要做的就是确保当有人从SurveyResponseBase 定义具体模型时，他们将ForeignKey 包含到从SurveyQuestionBase 定义的具体模型中

这是完整的代码：

from __future__ import unicode_literals


from django.contrib.contenttypes.fields import GenericForeignKey
from django.contrib.contenttypes.models import ContentType
from django.db import models

# Implementation borrows from: https://github.com/jessykate/django-survey/


class SurveyQuestionBase(models.Model):
    TEXT = 'text'
    INTEGER = 'integer'
    RADIO = 'radio'
    SELECT = 'select'
    MULTI_SELECT = 'multi-select'

    ANSWER_TYPE_CHOICES = (
        (INTEGER, 'Integer',),
        (TEXT, 'Text',),
        (RADIO, 'Radio',),
        (SELECT, 'Select',),
        (MULTI_SELECT, 'Multi-Select',),
    )

    question = models.TextField()
    required = models.BooleanField()
    question_type = models.CharField(choices=ANSWER_TYPE_CHOICES, max_length=20)

    class Meta:
        abstract = True


class SurveyResponseBase(models.Model):
    """
    concrete_question_model: 'app_label.Model' - Define the concrete model this question belongs to
    """
    concrete_model = 'SurveyQuestionBase'

    question = models.ForeignKey(concrete_model)
    response = models.TextField()

    class Meta:
        abstract = True

Answer 1

解决此问题的两种解决方案（均有效）：

第一个解决方案涉及使用GenericForeignKey。第二个更有趣，涉及动态生成SurveyResponseBase。

解决方案 1：使用 GenericForeignKey

class SurveyQuestionBase(models.Model):
    TEXT = 'text'
    INTEGER = 'integer'
    RADIO = 'radio'
    SELECT = 'select'
    MULTI_SELECT = 'multi-select'

    ANSWER_TYPE_CHOICES = (
        (INTEGER, 'Integer',),
        (TEXT, 'Text',),
        (RADIO, 'Radio',),
        (SELECT, 'Select',),
        (MULTI_SELECT, 'Multi-Select',),
    )

    question = models.TextField()
    required = models.BooleanField()
    question_type = models.CharField(choices=ANSWER_TYPE_CHOICES, max_length=20)

    class Meta:
        abstract = True

    @classmethod
    def get_subclasses(cls, *args, **kwargs):
        for app_config in apps.get_app_configs():
            for app_model in app_config.get_models():
                model_classes = [c.__name__ for c in inspect.getmro(app_model)]
                if cls.__name__ in model_classes:
                    yield app_model


class SurveyResponseBase(models.Model):
    content_type = models.ForeignKey(ContentType, on_delete=models.CASCADE, limit_choices_to=get_content_choices)
    object_id = models.PositiveIntegerField()
    content_object = GenericForeignKey('content_type', 'object_id')
    response = models.TextField()

    class Meta:
        abstract = True

def get_content_choices():
    query_filter = None

    for cls in SurveyQuestionBase.get_subclasses():
        app_label, model = cls._meta.label_lower.split('.')
        current_filter = models.Q(app_label=app_label, model=model)

        if query_filter is None:
            query_filter = current_filter
        else:
            query_filter |= current_filter

    return query_filter

解决方案 2：动态基类生成

class SurveyQuestionBase(models.Model):
    TEXT = 'text'
    INTEGER = 'integer'
    RADIO = 'radio'
    RATING = 'rating'
    SELECT = 'select'
    MULTI_SELECT = 'multi-select'

    QUESTION_TYPES = (
        (INTEGER, 'Integer'),
        (TEXT, 'Text'),
        (RADIO, 'Radio'),
        (RATING, 'Rating'),
        (SELECT, 'Select'),
        (MULTI_SELECT, 'Multi-Select'),
    )

    CHOICE_TYPES = (RADIO, RATING, SELECT, MULTI_SELECT)

    question = models.TextField()
    required = models.BooleanField()
    question_type = models.CharField(choices=QUESTION_TYPES, max_length=20)
    choices = models.TextField(blank=True, null=True)

    choices.help_text = """
    If the question type is "Radio," "Select," or "Multi-Select", 
    provide a comma-separated list of options for this question
    """

    class Meta:
        abstract = True


Meta = type('Meta', (object,), {'abstract': True})


def get_response_base_class(concrete_question_model):
    """
    Builder method that returns the SurveyResponseBase base class
    Args:
        concrete_question_model: Concrete Model for SurveyQuestionBase

    Returns: SurveyResponseBase Class
    """
    try:
        assert SurveyQuestionBase in concrete_question_model.__bases__
    except AssertionError:
        raise ValidationError('{} is not a subclass of SurveyQuestionBase'.format(concrete_question_model))

    attrs = {
        'question': models.ForeignKey(concrete_question_model, related_name='responses'),
        'response': models.TextField(),
        '__module__': 'survey_builder.models',
        'Meta': Meta(),
    }
    return type('SurveyResponseBase', (models.Model,), attrs)

我们决定继续使用解决方案 2，因为 GenericForeignKeys 方法需要额外的 ContentType 选择。

Answer 2

我相信您不能这样做，因为 ForeignKey 不知道要指向哪个实际模型。

您可能正在寻找 GenericForeignKey (https://docs.djangoproject.com/en/dev/ref/contrib/contenttypes/#generic-relations)。它允许您正确定义这种关系。