何时在ForeignKey上使用ManyToMany字段？ [英] When to use a ManyToMany field over a ForeignKey?

问题描述

考虑到我们有两个Django模型，问答。
一个问题可以有很多答案，但答案只能有一个与之相关的问题。
我们可以将关系建模为：

 类问题（models.Model）：
 text = models .CharField（...）
 answers = models.ManyToManyField（'Answer'）
 
类答案（models.Model）：
 text = models.CharField（... ）
  

我们也可以将其建模为：

  class Question（models.Model）：
 text = models.CharField（...）
 
 class答案（models.Model）：
 text = models.CharField（...）
 question = models.ForeignKey（'Question'）
  

Django经理允许我们向后追踪ForeignKey和ManyToManyField。
我们应该使用什么模型结构？

解决方案

一对多当然。您可以使用多对多关系来实现同样的事情，但是您会使事情变得复杂，您将为表演打击付出代价。

从数据库建模的角度来考虑它（忘记ORM）。你为什么要这样做：问题 - >多对多经理 - >答案而不是：问题 - >答案。

Consider that we have two Django models, Question and Answer. A question can have many answers to it, but an answer can have only one question related to it. We can model the relationship as:

class Question(models.Model):
    text     = models.CharField(...)
    answers  = models.ManyToManyField('Answer')

class Answer(models.Model):
    text     = models.CharField(...)

We can also model it as:

class Question(models.Model):
    text     = models.CharField(...)

class Answer(models.Model):
    text     = models.CharField(...)
    question = models.ForeignKey('Question')

Django managers allow us to follow both ForeignKey and ManyToManyField backwards. What model structure should we use?

解决方案

one-to-many of course. You could achieve the same thing using many-to-many relationship but you'll complicate things a lot and you'll pay for a performance hit.

Think of it from a database modelling point of view (forget the ORM). Why would you want to do: question -> many-to-many-manager -> answers instead of having: question -> answers.

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