通过Django查询多个多个字段 [英] Query for a ManytoMany Field with Through in Django

问题描述

  class Classification（models.Model）：
 name = models.CharField（choices = class_choices）
 ... 
 
类Activity（models.Model）：
 name = models.CharField（max_length = 300）
 fee = models.ManyToManyField（Classification，through ='Fee'）
 ... 
 
 class费用（models.Model）：
 activity = models.ForeignKey（Activity ）
 class = models.ForeignKey（Classification）
 early_fee = models.IntegerField（decimal_places = 2，max_digits = 10）
 regular_fee = models.IntegerField（decimal_places = 2，max_digits = 10）
  

想法是每个活动和分类对都会有一套费用。分类就像学生，工作人员等。

我知道这部分是正确的。

然后在我的应用程序中，我查询一组活动：

  activities = Activity.objects.filter（...）
  

哪个返回活动列表。我需要在我的模板中显示活动列表及其费用。这样的事情：

 活动名称
学生提前价格 -  $ 4 
学生常规价格 -  $ 5 
工作人员提前价格 -  $ 6 
工作人员常规价格 -  $ 8 
  

但是我不知道一个简单的方法来获取这个信息，而不需要每个活动/类对的费用对象的特定获取查询。

我希望这可以工作：

  activity.fee.all （）
  

但是只返回分类对象。有没有办法通过我已经查询的活动来获取配对的费用对象数据？

或者我这样做完全错了？

解决方案

考虑到michuk提示将费用重新命名为分类：

费用的默认名称活动模型上的对象将被收费。所以为了获得你的价格，请执行以下操作：

  for a in Activity.objects.all（）：
 a.fee_set.all（）#gets你所有的活动费
  

有一件事，因为你可以看到你最终会在每个活动对象上执行1个SELECT以获取费用，有一些可以帮助的应用程序，例如 django-batch-select 在这种情况下只执行2次查询。

I have a models in Django that are something like this:

class Classification(models.Model):
  name = models.CharField(choices=class_choices)
  ...

class Activity(models.Model):
  name = models.CharField(max_length=300)
  fee = models.ManyToManyField(Classification, through='Fee')
  ...

class Fee(models.Model):
  activity = models.ForeignKey(Activity)
  class = models.ForeignKey(Classification)
  early_fee = models.IntegerField(decimal_places=2, max_digits=10)
  regular_fee = models.IntegerField(decimal_places=2, max_digits=10)

The idea being that there will be a set of fees associated with each Activity and Classification pair. Classification is like Student, Staff, etc.

I know that part works right.

Then in my application, I query for a set of Activities with:

activities = Activity.objects.filter(...)

Which returns a list of activities. I need to display in my template that list of Activities with their Fees. Something like this:

Activity Name
Student Early Price - $4
Student Regular Price - $5
Staff Early Price - $6
Staff Regular Price - $8

But I don't know of an easy way to get this info without a specific get query of the Fees object for each activity/class pair.

I hoped this would work:

activity.fee.all()

But that just returns the Classification Object. Is there a way to get the Fee Object Data for the Pair via the Activities I already queried?

Or am I doing this completely wrong?

解决方案

Considering michuk's tip to rename "fee" to "classification":

Default name for Fee objects on Activity model will be fee_set. So in order to get your prices, do this:

for a in Activity.objects.all():
    a.fee_set.all() #gets you all fees for activity

There's one thing though, as you can see you'll end up doing 1 SELECT on each activity object for fees, there are some apps that can help with that, for example, django-batch-select does only 2 queries in this case.

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