Django如何创建指向同一个模型的多个外键？

如下所示的House模型，其”province“, "city"和"district"字段类型是指向Region模型的外键。

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class Region(models.Model):

"""行政区域表

国家，省，市，区（县）

"""

parent = models.ForeignKey('self')

name = models.CharField(max_length=30)

region_type = models.IntegerField()

class Meta:

db_table = "regions"

class House(models.Model):

"""房屋表

"""

province = models.ForeignKey(Region)

city = models.ForeignKey(Region)

district = models.ForeignKey(Region)

address = models.CharField(max_length=200)

name = models.CharField(max_length=200)

longitude = models.FloatField() # 经度

latitude = models.FloatField() # 纬度

created_at = models.DateTimeField(auto_now_add=True)

updated_at = models.DateTimeField(auto_now=True, null=True)

表面上看起来好像没有问题，但是进行syncdb时，就会出现”house.house: Accessor for field 'province' clashes with related field 'Region.house_set'. Add a related_name argument to the definition for 'province'....“错误。

原因是指向同一模型的三个外键反向关联名称产生了冲突，Region模型对province的反向关联名称为house_set()，对city的反向关联名称也是house_set()，对district的反向关联名称还是house_set()。

解决方法：给models.ForeignKey()加入related_name参数，定义不同的关联名称。如下代码：

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class House(models.Model):

"""房屋表

"""

province = models.ForeignKey(Region, related_name='province_houses')

city = models.ForeignKey(Region, related_name='city_houses')

district = models.ForeignKey(Region, related_name='district_houses')

address = models.CharField(max_length=200)

name = models.CharField(max_length=200)

longitude = models.FloatField() # 经度

latitude = models.FloatField() # 纬度

created_at = models.DateTimeField(auto_now_add=True)

updated_at = models.DateTimeField(auto_now=True, null=True)

参考文章：Relating
a model to another model more than once

Model source code

from django.db import models

class Person(models.Model):
full_name = models.CharField(max_length=20)
mother = models.ForeignKey('self', null=True, related_name='mothers_child_set')
father = models.ForeignKey('self', null=True, related_name='fathers_child_set')

def __unicode__(self):
return self.full_name

Sample API usage

This sample code assumes the above model has been saved in a file<tt literal"="">mysite/models.py.

>>> from mysite.models import Person

# Create two Person objects -- the mom and dad in our family.
>>> dad = Person(full_name='John Smith Senior', mother=None, father=None)
>>> dad.save()
>>> mom = Person(full_name='Jane Smith', mother=None, father=None)
>>> mom.save()

# Give mom and dad a kid.
>>> kid = Person(full_name='John Smith Junior', mother=mom, father=dad)
>>> kid.save()

>>> kid.mother
<Person: Jane Smith>
>>> kid.father
<Person: John Smith Senior>
>>> dad.fathers_child_set.all()
[<Person: John Smith Junior>]
>>> mom.mothers_child_set.all()
[<Person: John Smith Junior>]
>>> kid.mothers_child_set.all()
[]
>>> kid.fathers_child_set.all()
[]