Python | Django | モデルを用いたテーブル間の紐づけにおけるmany-to-manyの使い方

from django.db import models
from django.utils import timezone

class
Date(models.Model):
# 抽象基底クラス
  create_date = models.DateTimeField(default=timezone.now)
  update_date = models.DateTimeField(default=timezone.now)
class
Meta:
    abstract =
True
class
Cake(Date):
  cake_name = models.CharField(max_length=40)
  birthplace = models.CharField(max_length=40)
  birthday = models.DateField(default='1900-01-01')
  inventor = models.CharField(max_length=40)
  sales_amounts = models.IntegerField()
  like = models.BooleanField(default=True)
  email = models.EmailField(db_index=True)
  web_site = models.URLField()
  feed_back = models.TextField(null=True,blank=True)
class
Meta:
    db_table =
'cake'
    index_together =
[['cake_name','inventor']]
    ordering =
['birthday']
def
__str__(self):
return
f'{self.cake_name}'

class Dorayakis(models.Model):
  name = models.CharField(max_length=30)
  price = models.IntegerField()
  birthday = models.DateField(default='1900-01-01')
  shop = models.ForeignKey(
    'Shops', on_delete=models.RESTRICT
  )
  city = models.ForeignKey(
    'Cities', on_delete=models.CASCADE
  )

  class
Meta:
    db_table =
'dorayakis'

class Shops(models.Model):
  name = models.CharField(max_length=30)
  city = models.ForeignKey(
    'Cities', on_delete=models.CASCADE
  )

  class
Meta:
    db_table =
'shops'
class
Cities(models.Model):
  name = models.CharField(max_length=30)
class
Meta:
    db_table =
'cities'


class Places(models.Model):
  name = models.CharField(max_length=50)
  address = models.CharField(max_length=80)

  class Meta:
    db_table = 'places'

class Companies(models.Model):
  place = models.OneToOneField(
    Places,
    on_delete=models.CASCADE,
    primary_key=True
  )
  name = models.CharField(max_length=50)

  class Meta:
    db_table = 'companies'

class Musics(models.Model): # 以下追記箇所
  name = models.CharField(max_length=50)

  def __str__(self):
    return self.name

  class Meta:
    db_table = 'musics'

class Musicians(models.Model):
  name = models.CharField(max_length=30)
  musics = models.ManyToManyField(Musics) # ManyToManyFieldの利用

  def __str__(self):
    return self.name

  class Meta:
    db_table = 'musicians'

(djangoenv) C:\Users\shiro\Desktop\210517_python development\mymodeltest\model_project
>python manage.py makemigrations --name add_music_musician # 入力箇所

Migrations for 'model_app': # 以下出力箇所
  model_app\migrations\0004_add_music_musician.py
    - Create model Musics
    - Create model Musicians

(djangoenv) C:\Users\shiro\Desktop\210517_17_python development\mymodeltest\modelpjepython develop_project
>python manage.py migrate model_app # 入力箇所

Operations to perform: 以下出力箇所
  Apply all migrations: model_app
Running migrations:
  Applying model_app.0004_add_music_musician... OK

import os
os.environ.setdefault('DJANGO_SETTINGS_MODULE','model_project.settings')

from django import setup
setup()

from model_app.models import Musicians, Musics

def adding_musics():
music1 = Musics(name='Tokyo Gird')
music2 = Musics(name='Love Me Do')
music3 = Musics(name='Viva la Vida')
music4 = Musics(name='Life Is a Flower')
music5 = Musics(name='She Loves You')
music1.save()
music2.save()
music3.save()
music4.save()
music5.save()

def adding_musicians():
musician1 = Musicians(name='Ace of Base')
musician2 = Musicians(name='The Beatles')
musician3 = Musicians(name='ColdPlay')
musician1.save()
musician2.save()
musician3.save()

adding_musics() # musicsに値を追加
adding_musicians() # musicianに値を追加

musician1 = Musicians.objects.get(pk=1)
music1 = Musics.objects.get(pk=1)
music4 = Musics.objects.get(pk=4)

musician2 = Musicians.objects.get(pk=2)
music2 = Musics.objects.get(pk=2)
music5 = Musics.objects.get(pk=5)

musician3 = Musicians.objects.get(pk=3)
music3 = Musics.objects.get(pk=3)

musician1.musics.add(music1, music4) # musicians_musicsに値を追加
musician2.musics.add(music2, music5)
musician3.musics.add(music3)

<QuerySet [<Musics: Tokyo Gird>, <Musics: Life Is a Flower>]> # musician1と紐づくmusic
<QuerySet [<Musics: Love Me Do>, <Musics: She Loves You>]> # musician2と紐づくmusic
<QuerySet [<Musics: Viva la Vida>]> # musician3と紐づくmusic