Django - 如何从具有外键的 model 中获取所有项目？

Question

I'm creating two models: Feedstockformula and formula. This is the code for each one:

FeedstockFormula:

from django.db import models

class FeedstockFormulas(models.Model):
    ratio = models.FloatField()
    feedstock = models.OneToOneField("dashboard.Feedstock", on_delete=models.CASCADE, default="0")
    formulas = models.ForeignKey("dashboard.Formulas", on_delete=models.CASCADE, default="")

Formula:

from django.db import models

class Formulas(models.Model):
    name = models.CharField(max_length=100)
    cost = models.FloatField()
    weight = models.FloatField()

How can I get all the FeedstockFormulas that is part of a Formula?

Answer 1

You should add "related_name" to formulas field in FeedstockFormulas.

Like this:

formulas = models.ForeignKey("dashboard.Formulas", related_name="feed_stock_formulas",on_delete=models.CASCADE, default="")

Django use reverse relation on ForeignKey, you can access all FeedstockFormulas that is part of a Formula by writing this:

Formulas.feed_stock_formulas

Answer 2

You can access the FeedstockFormulas via the related_name of your formulas field, which defaults to feedstockformulas_set in your case.

For example:

formula = Formulas.objects.first()
print(formula.feedstockformulas_set.all().feedstock)

Answer 3

You could do it like this

First get a reference to the formula you want with something like

f = Formula.objects.get(name = <formula name>)

Then you use it to get the feedstockformulas

fsf = FeedstockFormulas.objects.filter(formulas = f)