问值错误:无法分配"<ContentType: config>"：当前数据库路由器阻止此关系

EN

DATABASE_ROUTERS = ['routers.db_routers.AppRouter']
DATABASE_APPS_MAPPING = {'product': 'postgres',}

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.sqlite3',
        'NAME': BASE_DIR / 'db.sqlite3',
    },
    'postgres': {
        'ENGINE': 'django.db.backends.postgresql',
        'NAME': 'product',
        'USER': 'postgres',
        'PASSWORD':'password',
        'HOST':'localhost'
    }

}

class AppRouter:
    """
    A router to control all database operations on models in the
    product application.
    """
    def db_for_read(self, model, **hints):
        """
        Attempts to read user models go to postgres.
        """
        if model._meta.app_label == 'product':
            return 'postgres'
        return 'default'

    def db_for_write(self, model, **hints):
        """
        Attempts to write user models go to postgres.
        """
        if model._meta.app_label == 'product':
            return 'postgres'
        return 'default'

    def allow_relation(self, obj1, obj2, **hints):
        """
        Allow relations if a model in the user app is involved.
        """
        if obj1._meta.app_label == 'product' or \
           obj2._meta.app_label == 'product':
           return True
        return False

    def allow_migrate(self, db, app_label, model_name=None, **hints):
        """
        Make sure the auth app only appears in the 'product_db'
        database.
        """
        if app_label == 'product':
            return db == 'postgres'
        return None

class Product(models.Model):
    name = models.CharField(max_length=100)
    price = models.DecimalField(max_digits=10, decimal_places=2)
    weight = models.DecimalField(max_digits=10, decimal_places=2)
    created_at = models.DateTimeField(auto_now_add=True)
    updated_at = models.DateTimeField(auto_now=True)
    
    class Meta:
        app_label = 'product'
    
    def __str__(self):
        return self.name