从模型FK到Django中另一个模型的外部FK

Question

I have model "Cities" in "external_app" app like this:

class Cities(models.Model):
CityName = models.CharField(max_length=50, blank=False, db_index=True)
slug = models.SlugField(max_length=50, db_index=True, unique=True)

I have second app, "Address_program" with few models:

class CityRegions(models.Model):
    city = models.ForeignKey('external_app.Cities', default=0, verbose_name=' City', related_name='City_for_region')
    city_region = models.CharField(max_length=200, blank=False, default='', verbose_name='City region', unique=True)
    city_region_slug = models.SlugField(verbose_name='City region slug')

and second model for sub-regions in region. Now I want to publish used cities in CityRegions model. I try to add FK for city field

class RegionSquares(models.Model):
city = models.ForeignKey(CityRegions, default=0, verbose_name='City', related_name='City_for_regionsquare', to_field='city')
region = models.ForeignKey(CityRegions, default=0, verbose_name='City region',related_name='Region')
    region_square = models.CharField(max_length=200, blank=False, default='', verbose_name='City sub-region')
    region_square_slug = models.SlugField(verbose_name='City sub-region slug')

when I try to make migrations I get error with message "(fields.E311) 'CityRegions.city' must set unique=True because it is referenced by a foreign key".

When I set unique=True in CityRegions.City field and try to migrate I get error with message: "django.db.utils.IntegrityError: UNIQUE constraint failed..."

Question is how to publish list of used in CityRegions model cities in RegionSquares model?

In common app should have few models: - editanle lists of city regions with current city (region and city should be show) - editable sub-reqions list for every city region (city, region and sub-region should be show) - editable list of streets (city, region and sub-region should be shown)

Scheme:

**cities** (model. Used in another apps of the project)
  |-->**citie's regions** (parent for sub-regions) (city and region should me show in admin)
      |--> **region's sub-regions** (parent for streets) (city,region and sub-region should me show in admin)
          |--> **list of streets** (city,region, sub-region and street should me show in admin)

Sample data:

**Cities:** Moscow, Novosibirsk, Kemerovo
**Regions (city is parent):** Moscow - SVAO, Moscow - TSAO, Novosibirsk - Centralnij, Kemerovo - Jugniy
**Sub regions (City and region are parents):** Moscow - SVAO - sub-region A; Moscow - SVAO - subregion B; Moscow - SVAO sub-region C. Novosibirsk - Centralnij - sub-region A. Novosibirsk - Centralnij - sub-region B
**Streets (City, region and sub-region are parents):** Moscow - SVAO - sub-region A - street A; Moscow - SVAO - sub-region A - street B; Moscow - SVAO - sub-region A - street C; Novosibirsk - Centralnij - sub-region B -s treet A; Novosibirsk - Centralnij - sub-region B street B... and so on

Desired result:

Moscow
   Moscow - SVAO
     Moscow - SVAO - sub-region A
         Moscow - SVAO - sub-region A - street A
         Moscow - SVAO - sub-region A - street B
         Moscow - SVAO - sub-region A - street C
     Moscow - SVAO - sub-region B
         Moscow - SVAO - sub-region B - street A
         Moscow - SVAO - sub-region B - street B
         Moscow - SVAO - sub-region B - street C
     Moscow - SVAO - sub-region C
         Moscow - SVAO - sub-region C - street A
         Moscow - SVAO - sub-region C - street B
         Moscow - SVAO - sub-region C - street C
Novosibirsk
   Novosibirsk - Centralnij
     Novosibirsk - Centralnij - sub-region A - street A
     Novosibirsk - Centralnij - sub-region A - street B
     Novosibirsk - Centralnij - sub-region A - street C

and so on...

I using Django 1.11 and python 2.7.10

Answer 1

迁移失败的原因可能是您具有同一个city多个CityRegions

Answer 2

city is not the PK (primary key) of CityRegions, so you should not refer it. Uniqueness fails because there are already repetative values - which is fine.

To make it work:

a) normalize your data model and remove city field from RegionSquares - achieve it via region when needed. Like CityRegions.objects.filter(region__city__CityName='Moscow')

or

b) reference City model itself:

class RegionSquares(models.Model):
    city = models.ForeignKey('external_app.Cities', default=0, verbose_name=' City', related_name='City_for_region')
    ...

equally to CityRegions definition of this field.

upd

Again, if you question is still about how to model demonstrated relations (and get rid of all the errors mentioned in your question), then the answer is already here - remove city field from RegionSquares model. You already have there link to region which (the region record) contains city value. This is option a described above.