Django models - how to assign as ForeignKey - django

Question

My lab has a models.py as below:
class Book(models.Model):
isbn = models.CharField(max_length=10, unique=True)
name = models.CharField(max_length=100)
published_year = models.IntegerField()
total_qty = models.IntegerField()
current_qty = models.IntegerField()
max_duration = models.IntegerField()
author = models.ForeignKey(Author, on_delete=models.PROTECT)
category = models.ForeignKey(Category, on_delete=models.PROTECT)
def __str__(self):
return self.name
class BookCopy(models.Model):
class Status:
AVAILABLE = 1
BORROW =2
LOST = 3
barcode = models.CharField(max_length=30, unique=True)
buy_date = models.DateField(null=True, blank=True)
status = models.IntegerField()
book = models.ForeignKey(Book, on_delete=models.PROTECT)
def __str__(self):
return self.barcode
class User(models.Model):
username = models.CharField(max_length=30, unique=True)
fullname = models.CharField(max_length=100, null=True)
phone = models.CharField(max_length=10, null=True)
def __str__(self):
return self.fullname
class BookBorrow(models.Model):
class Status:
BORROWING = 1
RETURNED = 2
borrow_date = models.DateField()
deadline = models.DateField()
return_date = models.DateField(null=True)
status = models.IntegerField()
book_copy = models.ForeignKey(BookCopy, on_delete=models.PROTECT)
book_name = models.ForeignKey(Book, on_delete=models.PROTECT)
user = models.ForeignKey(User, on_delete=models.PROTECT)
And i wrote the api for borrow_book function like below:
#csrf_exempt
def muon_sach(request):
body = request.POST
username = body.get('username')
barcode = body.get('barcode')
user = User.objects.filter(username=username).first()
bookcopy = BookCopy.objects.filter(barcode = barcode).first()
if not user:
return HttpResponse(json.dumps({
'error':"Nguoi dung khong ton tai"
}))
if not bookcopy:
return HttpResponse(json.dumps({
'error':"ma sach khong ton tai"
}))
book_borrow = BookBorrow()
# resp = []
book_borrow.user = user
book_borrow.book_copy = bookcopy
book_borrow.borrow_date = datetime.now()
book_borrow.deadline = datetime.now() + timedelta(days=bookcopy.book.max_duration)
book_borrow.status = BookBorrow.Status.BORROWING
book_borrow.book_name = bookcopy.book.name
book_borrow.save()
bookcopy.status = BookCopy.Status.BORROW
bookcopy.save()
bookcopy.book.current_qty -=1
bookcopy.book.save()
return HttpResponse(json.dumps({'success':True}))
however when i test with postman (give username and barcode), it gets the error
xxx "BookBorrow.book_name" must be a "Book" instance."
Could you please advise where incorrect and assist me correct it ? Appreciate for any assist

Answer 1

You have to do the following:
#csrf_exempt
def muon_sach(request):
# ... more code here
bookcopy = BookCopy.objects.filter(barcode = barcode).first()
book_borrow.book_name = bookcopy.book
book_borrow.save()
# ... more code here
return HttpResponse(json.dumps({'success':True}))
So in the definition of your model you can see that book_name has the following structure:
class BookBorrow(models.Model):
# ... More code here
book_name = models.ForeignKey(Book, on_delete=models.PROTECT)
user = models.ForeignKey(User, on_delete=models.PROTECT)
It is clear that BookBorrow.book_name must accept a Book instance. So when you pass in you code book_borrow.book_copy = bookcopy it is passing a BookCopy instance so that's the error.
borrow_copy.book is the appropiate.

Answer 2

You have specified book_name to be a Foreign Key to Book, and you try to assign to it the book.name value.
Either you need to set this field as a CharField or you need to rename the field from book_name to book and use book_borrow.book = bookcopy.book