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用于在我们网站上实施特定调查的新具体模型。我遇到的问题是强制执行SurveyResponseBase模型，如果具体，应该为ForeignKey的具体模型定义SurveyQuestionBase。

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None或app_label.ModelName。

一个hacky修复方法是创建一个新的具体模型SurveyQuestionConcrete并使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，他们会将ForeignKey包含在SurveyQuestionBase

定义的具体模型中

这里是完整的代码：

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（均可使用）：

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

我相信你不能这样做，因为ForeignKey不知道指向什么样的实际模型。

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

使用ForeignKey将Abstract模型定义到另一个抽象模型

2 个答案: