django orm 中objects.create() 和object.save() 的区别

Question

u = UserDetails.objects.create(first_name='jake',last_name='sullivan')
u.save()

UserDetails.objects.create() and u.save() both perform the same save() function. What is the difference? Is there any extra check or benefit in using create() vs save() ?

Similar questions:

• What's the best way to create a model object in Django?
• Django: Difference between save() and create() from transaction perspective
• Django Model() vs Model.objects.create()

Answer 1

The Django documentation says it is the same . It is just more convenient to make it on one line. You could make a save() on one line too, but it would be more verbose and less readable -- it is clear you are creating a new object with the create() method.

create(**kwargs)

A convenience method for creating an object and saving it all in one step. Thus:

 p = Person.objects.create(first_name="Bruce", last_name="Springsteen")

and:

 p = Person(first_name="Bruce", last_name="Springsteen") p.save(force_insert=True)

are equivalent.

The force_insert parameter is documented elsewhere, but all it means is that a new object will always be created. Normally you won't need to worry about this. However, if your model contains a manual primary key value that you set and if that value already exists in the database, a call to create() will fail with an IntegrityError since primary keys must be unique. Be prepared to handle the exception if you are using manual primary keys.

Answer 2

Similar question: Django Model() vs Model.objects.create()

The difference between Model() vs Model.objects.create() are summarized as below.

---

1. .save() perform internally as either INSERT or UPDATE object to db, while .objects.create() perform only INSERT object to db.

   Model.save() perform ....

   UPDATE → If the object's primary key attribute is set to a value that evaluates to True

   INSERT → If the object's primary key attribute is not set or if the UPDATE didn't update anything (eg if primary key is set to a value that doesn't exist in the database).

---

2. If primary key attribute is set to a value then Model.save() perform UPDATE but Model.objects.create raise IntegrityError .

   eg.

   models.py

    class Subject(models.Model): subject_id = models.PositiveIntegerField(primary_key=True, db_column='subject_id') name = models.CharField(max_length=255) max_marks = models.PositiveIntegerField()

   1) Insert/Update to db with Model.save()

   physics = Subject(subject_id=1, name='Physics', max_marks=100) physics.save() math = Subject(subject_id=1, name='Math', max_marks=50) # Case of update math.save()

   Output:

    Subject.objects.all().values() <QuerySet [{'subject_id': 1, 'name': 'Math', 'max_marks': 50}]>

   2) Insert to db with Model.objects.create()

   Subject.objects.create(subject_id=1, name='Chemistry', max_marks=100) IntegrityError: UNIQUE constraint failed: m****t.subject_id

   Explanation: Above math.save() is case of update since subject_id is primary key and subject_id=1 exists django internally perform UPDATE , name Physics to Math and max_marks from 100 to 50 for this, but objects.create() raise IntegrityError

---

3. Model.objects.create() not equivalent to Model.save() however same can be achieved with force_insert=True parameter on save method ie Model.save(force_insert=True) .

---

4. Model.save() return None where Model.objects.create() return model instance ie package_name.models.Model

---

Conclusion: Model.objects.create() internally do model initialization and perform save with force_insert=True .

source-code block of Model.objects.create()

def create(self, **kwargs):
    """
    Create a new object with the given kwargs, saving it to the database
    and returning the created object.
    """
    obj = self.model(**kwargs)
    self._for_write = True
    obj.save(force_insert=True, using=self.db)
    return obj

The following links can be followed for more details:

1. https://docs.djangoproject.com/en/stable/ref/models/querysets/#create

2. https://github.com/django/django/blob/2d8dcba03aae200aaa103ec1e69f0a0038ec2f85/django/db/models/query.py#L440

Note: Above answer is from question .