Error: No module named 'mysite.books'
Solution: delete mysite in settings.py, directly 'books',
错误： __init__() missing 1 required positional argument: 'on_delete'
解决：publisher = models.ForeignKey(Publisher,on_delete=models.CASCADE)
Added in parentheses, on_delete=models.CASCADE
Problem: python manage.py validate reports an error
Solution: python manage.py check instead
Used to detect database changes and generate database migration files:
python manage.py makemigrations books
To migrate the database:
python manage.py migrated
Used to convert database migration files into database languages
python manage.py sqlmigrate books 0001
In Django, if you are using Python3, you can only use the __str__ method, and if you are using Python2, you can use the __unicode__ method. Because it is safer.
The filter() function in publisher.objects.filter() returns a recordset
get() returns a single object, multiple or non-existent will be an error, use try--except--else