Django で Primary Key を使う時の ForeignKey の使い方

モデルで、Primary Key を使うようにした時の ForeignKey の使い方です。

1. models.py

to_field を指定する必要があります。

models.py

from django.db import models
from django.urls import reverse

class Member(models.Model):
    id_member = models.CharField(max_length=10,primary_key=True)
    name = models.CharField(max_length=20)
    year_of_birth = models.IntegerField(null=True)

    team = models.ForeignKey('Team', to_field='id_team', on_delete=models.SET_NULL, null=True)

    def __str__(self):
        return self.name

    def get_absolute_url(self):
        return reverse('member-detail', args=[str(self.id_member)])

class Team(models.Model):
    id_team = models.CharField(max_length=10,primary_key=True)
    name = models.CharField(max_length=20)
    home = models.CharField(max_length=20)

    def get_absolute_url(self):
        return reverse('team-detail', args=[str(self.id_team)])

    def __str__(self):
        return f'{self.name}'

1. urls.py

Primary Key を 文字列にしたので、
slug:pk　にする必要があります。

urls.py

from django.urls import path
from . import views

urlpatterns = [
    path('', views.index, name='index'),
    path('members/', views.MemberListView.as_view(), name='members'),
    path('member/<slug:pk>', views.MemberDetailView.as_view(), name='member-detail'),
    path('teams/', views.TeamListView.as_view(), name='teams'),
    path('team/<slug:pk>', views.TeamDetailView.as_view(), name='team-detail'),
]
#
urlpatterns += [  
    path('member/create/', views.MemberCreate.as_view(), name='member_create'),
    path('member/<slug:pk>/update/', views.MemberUpdate.as_view(), name='member_update'),
    path('member/<slug:pk>/delete/', views.MemberDelete.as_view(), name='member_delete'),
]
#

1. データベースのテーブルは次のようになります。

member

+---------------+-------------+------+-----+---------+-------+
| Field         | Type        | Null | Key | Default | Extra |
+---------------+-------------+------+-----+---------+-------+
| id_member     | varchar(10) | NO   | PRI | NULL    |       |
| name          | varchar(20) | NO   |     | NULL    |       |
| year_of_birth | int(11)     | YES  |     | NULL    |       |
| team_id       | varchar(10) | YES  | MUL | NULL    |       |
+---------------+-------------+------+-----+---------+-------+

team

+---------+-------------+------+-----+---------+-------+
| Field   | Type        | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| id_team | varchar(10) | NO   | PRI | NULL    |       |
| name    | varchar(20) | NO   |     | NULL    |       |
| home    | varchar(20) | NO   |     | NULL    |       |
+---------+-------------+------+-----+---------+-------+

1. 次の環境で確認しました。

$ python --version
Python 3.7.2
$ python -m django --version
2.1.7