CODEWITHSUNDEEP
djangodjango-queryset
Aamu
Aamu

Reputation: 3611

django - What does created mean?

Will someone please explain to me about created, and where and how its being used in django.

I have seen it using in something like this:

obj, created = Person.objects.get_or_create(first_name=’John’, last_name=’Lennon’, defaults={’birthday’: date(1940, 10, 9)})

And even in signals:

@receiver(post_save, sender=Article)
def create_approval(sender, **kwargs):
    if kwargs.get("created", False):
        approval = Approval.objects.create(article_id=kwargs.get('instance').id)

I really need to know this. Any help will be much appreciated. Thank you.

Edit:

Here, from the above codes:

    if kwargs.get("created", False):

What does created mean here? Does it specify the value of created as False. Or what?

Upvotes: 2

Views: 415

Answers (2)

karthikr
karthikr

Reputation: 99640

Django's models gives a convenience method called get_or_create, which looks up for an object based on specified criteria (in kwargs). If the criteria do not match, a new object is created.

Now, there is no way for us to determine in the view if the object returned was created or pre-existing (especially if you dont have a created_datetime or similar field), hence the created. It is a boolean variable, which is set to True if a new object was created by the ORM, and set to False if an existing object was retrieved.

Now, in your scenario:

obj, created = Person.objects.get_or_create(first_name=’John’, last_name=’Lennon’, defaults={’birthday’: date(1940, 10, 9)})

This is saying, get me the Person object with first_name = John, last_name = Lennon, birthday = ...

If this is not found, create a new one for me.

The defaults specify the initial value of the field birthday while creating the object in this scenario.

This is also equivalent of writing

obj = None
try:
    obj = Person.objects.get(first_name=’John’, last_name=’Lennon’)
except Person.DoesNotExist:
    obj = Person.objects.create(’birthday’ = date(1940, 10, 9), first_name='John', last_name = 'Lennon')

In the signal's receiver, kwargs is a dictionary with custom key-value pairs. When you look at the signals' documentation, lets say post_save has the following signature

django.db.models.signals.post_save

post_save(sender, instance, created, raw, using, update_fields)

This s the same as

post_save(sender, **kwargs) #where the rest of the args are a dictionary saved in **kwargs

Here, created has a similar meaning. It is notifying the signal whether instance was newly created, or updated.

So, if created = True, new object was created. created=False, object was probably updated.

Upvotes: 5

guettli
guettli

Reputation: 27855

created is a boolean return variable of get_or_create(). If the object was created (SQL INSERT) with the get_or_create() call it is True, if not (the object was fetched with SELECT) it is False.

The second: MyModel.objects.create() forces a create (INSERT).

Upvotes: 0

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