class Author(models.Model):
    name = models.CharField('author name', max_length=100)

    def __str__(self):
        return self.name


class Book(models.Model):
    name = models.CharField('book name', max_length=100)
    authors = models.ManyToManyField(to=Author)

    def __str__(self):
        return self.name


class Store(models.Model):
    name = models.CharField('store name', max_length=100)
    books = models.ManyToManyField(to=Book, through='BookStore')

    def __str__(self):
        return self.name


class BookStore(models.Model):
    book = models.ForeignKey(to=Book, on_delete=models.CASCADE)
    store = models.ForeignKey(to=Store, on_delete=models.CASCADE)

    publisher_choices = (
        ('MF', "Mif"),
        ('AP', "Alpina"),
    )

    publisher = models.CharField(max_length=100, choices=publisher_choices)