在Django关系中来回走动

Question

I have following relations in between django models

class Customer(models.Model):
    #fields

class Tooth(models.Model):
    #fields
    customer = models.ForeignKey(Customer)

class Peri(models.Model):
    #fields
    customer = models.ForeignKey(Customer)

class PeriTask(models.Model):
    #fields
    tooth = models.ForeignKey(Tooth, related_name="peritasks")
    peri = models.ForeignKey(Peri, related_name="peritasks")

I can't seem to be able to grasp the inverse relations. I mean I can get all the peritasks a specific tooth is part of with `tooth.peritasks.all(). But given a specific Peri instance how can I filter the teeth that are part of that peri?Something like (I know its not correct)

Tooth.objects.filter(peritask__peri=peri) #this won't work I know just as an example to show what I mean   

Answer 1

You in fact have a many to many relationship between Peri and Tooth thru the PeriTask model. The simplest thing to do would be to explicitely declare this relationship (in either Tooth or Peri ) so the orm knows about it an add the appropriate descriptor to your models, cf https://docs.djangoproject.com/en/1.7/topics/db/models/#intermediary-manytomany :

class Tooth(models.Model):
    #fields
    customer = models.ForeignKey(Customer)
    peris = models.ManyToManyField("Peri", through="PeriTask")

Then you have access to a given peri 's related theeth with peri.tooth.all() .