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Hello, Django lovers!
Welcome to another interesting blog article in which I will discuss some typical model mistakes that you may find when working with Django and how to simply solve them. Django models are powerful and adaptable, but they have specific rules and conventions that must be followed in order to avoid mistakes and exceptions. In this essay, I'll show you several examples of these problems as well as how to remedy them in a few simple steps.
Let's get this party started!
1. FieldDoesNotExist exception
When you try to access a field that does not exist on your model or its parents, this exception is thrown. For instance, consider the following model:python
class Book(models.Model):title = models.CharField(max_length=100)author = models.ForeignKey(Author, on_delete=models.CASCADE)And you try to do something like this:book = Book.objects.get(id=1)print(book.genre)
You will get a FieldDoesNotExist exception because there is no field named genre on the Book model.
To resolve this, either add the field to your model or use an alternative field name that already exists on your model.
2. MultipleObjectsReturned exception
When you use the get() method to retrieve a single object from the database, but there are many objects that match your query, this exception is thrown. For instance, consider the following model:
class Author(models.Model):name = models.CharField(max_length=100)email = models.EmailField(unique=True)And you try to do something like this:author = Author.objects.get(name='John')
You will get a MultipleObjectsReturned exception if there are more than one authors with the name 'John' in the database. To fix this, you need to either use a more specific query that returns only one object, such as using the email field instead of the name field, or use a different method that returns a queryset instead of a single object, such as filter() or all().
3. DoesNotExist exception
When you use the get() method to retrieve a single object from the database, but there are many objects that match your query, this exception is thrown. For instance, consider the following model:
class Book(models.Model):title = models.CharField(max_length=100)author = models.ForeignKey(Author, on_delete=models.CASCADE)And you try to do something like this:book = Book.objects.get(title='The Catcher in the Rye')
If there are no books with that title in the database, you will receive a DoesNotExistException. To correct this, use a different query that returns an existent object, or handle the problem with a try/except block and provide an alternative action.
I hope you found this blog post useful and learned something new about Django models and how to handle common errors and exceptions. Please leave a remark if you have any queries or feedback. Have fun coding!
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