How to Use the Latest & Earliest Methods in Django QuerySet

Table of Content

• How to Use the Latest & Earliest Methods in Django QuerySet
• Additional Information on earliest and latest methods
• Wrap Off

Django API offers two methods earliest and latest methods, which are similar to the QuerySet methods first and last.

They are convenience methods that can be used to enhance the readability of the code.

There are two ways to use it:

1. Using the model's Meta class
   The best way to use latest methods is to define get_latest_by in the model's Meta class:

   class Book(models.Model):
       title = models.CharField(max_length=100)
       author = models.ForeignKey(User, on_delete=models.CASCADE)
       published = models.DateTimeField(blank=True, null=True)
       updated = models.DateTimeField(blank=True, null=True)
   
       class Meta:
           get_latest_by = 'published'
   

   Here's how you will use it:

   latest_book = Book.objects.latest()
   earliest_book = Book.objects.earliest()
   

2. Using it when accessing the objects

   You can pass the latest or earliest methods as a parameter on the fly when calling the query set:

   last_updated = Book.objects.latest('updated')
   

Additional Information on earliest and latest methods

The earliest and latest methods will raise a DoesNotExist exception if there is no object with the given parameters, that is, if the table is empty, or the filtered criteria returned no result.

It is slightly different from first and last, because they return None if there is no matching object.

You should also know that the earliest and latest methods might return instances with null dates.

But the thing is, the ordering behavior is not consistent between the different databases.

So you might want to remove null dates, like so:

Book.objects.filter(updated__isnull=False).latest('updated')

Typically, it is used with either DateField, DateTimeField or IntegerField.

It will also work with other field types.

But you should avoid it because it will be semantically wrong since the earliest and latest methods are available for convenience and to enhance readability.

This means that using them for something different from dates will cause more confusion.

Wrap Off

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