Django Model() vs Model.objects.create()

python django database django-models

275,810

Solution 1

https://docs.djangoproject.com/en/stable/topics/db/queries/#creating-objects

To create and save an object in a single step, use the create() method.

Solution 2

The differences between Model() and Model.objects.create() are the following:

INSERT vs UPDATE

Model.save() does either INSERT or UPDATE of an object in a DB, while Model.objects.create() does only INSERT.

Model.save() does
- 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 (e.g. if primary key is set to a value that doesn’t exist in the database).

Existing primary key

If primary key attribute is set to a value and such primary key already exists, then Model.save() performs UPDATE, but Model.objects.create() raises IntegrityError.

Consider the following 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()
```
  Result:
```
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: In the example, math.save() does an UPDATE (changes name from Physics to Math, and max_marks from 100 to 50), because subject_id is a primary key and subject_id=1 already exists in the DB. But Subject.objects.create() raises IntegrityError, because, again the primary key subject_id with the value 1 already exists.

Forced insert

Model.save() can be made to behave as Model.objects.create() by using force_insert=True parameter: Model.save(force_insert=True).

Return value

Model.save() return None where Model.objects.create() return model instance i.e. package_name.models.Model

Conclusion: Model.objects.create() does model initialization and performs save() with force_insert=True.

Excerpt from the source code 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

For more details follow the links:

Solution 3

The two syntaxes are not equivalent and it can lead to unexpected errors. Here is a simple example showing the differences. If you have a model:

from django.db import models

class Test(models.Model):

    added = models.DateTimeField(auto_now_add=True)

And you create a first object:

foo = Test.objects.create(pk=1)

Then you try to create an object with the same primary key:

foo_duplicate = Test.objects.create(pk=1)
# returns the error:
# django.db.utils.IntegrityError: (1062, "Duplicate entry '1' for key 'PRIMARY'")

foo_duplicate = Test(pk=1).save()
# returns the error:
# django.db.utils.IntegrityError: (1048, "Column 'added' cannot be null")

Solution 4

UPDATE 15.3.2017:

I have opened a Django-issue on this and it seems to be preliminary accepted here: https://code.djangoproject.com/ticket/27825

My experience is that when using the Constructor (ORM) class by references with Django 1.10.5 there might be some inconsistencies in the data (i.e. the attributes of the created object may get the type of the input data instead of the casted type of the ORM object property) example:

models

class Payment(models.Model):
     amount_cash = models.DecimalField()

some_test.py - object.create

Class SomeTestCase:
    def generate_orm_obj(self, _constructor, base_data=None, modifiers=None):
        objs = []
        if not base_data:
            base_data = {'amount_case': 123.00}
        for modifier in modifiers:
            actual_data = deepcopy(base_data)
            actual_data.update(modifier)
            # Hacky fix,
            _obj = _constructor.objects.create(**actual_data)
            print(type(_obj.amount_cash)) # Decimal
            assert created
           objs.append(_obj)
        return objs

some_test.py - Constructor()

Class SomeTestCase:
    def generate_orm_obj(self, _constructor, base_data=None, modifiers=None):
        objs = []
        if not base_data:
            base_data = {'amount_case': 123.00}
        for modifier in modifiers:
            actual_data = deepcopy(base_data)
            actual_data.update(modifier)
            # Hacky fix,
            _obj = _constructor(**actual_data)
            print(type(_obj.amount_cash)) # Float
            assert created
           objs.append(_obj)
        return objs

Solution 5

Model.objects.create() creates a model instance and saves it. Model() only creates an in memory model instance. It's not saved to the database until you call the instance's save() method to save it. That's when validation happens also.

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275,810

Author by

0leg

Updated on July 22, 2022

Comments

0leg almost 2 years
What it the difference between running two commands:
```
foo = FooModel()
```
and
```
bar = BarModel.objects.create()
```
Does the second one immediately create a BarModel in the database, while for FooModel, the save() method has to be called explicitly to add it to the database?
Nils about 7 years

The django docs are a bit contradictory on this point in my opinion. I've had the same question and read "Note that instantiating a model in no way touches your database; for that, you need to save()." docs.djangoproject.com/en/1.10/ref/models/instances/…
danidee about 7 years

I don't see that as contradictory. Generally in python, You instantiate objects by putting brackets after the Objects name not by a create method
Nakamura almost 6 years

@danidee I agree it is not contradictory, but it is certainly misleading. Mainly because in Nils 's link, example1 is "instantiating" but example2 is "instantiating+saving". Also, why should I refer to "queries" doc when I want to know how to save a model? There are really a lot of pains in django doc.
Juanjo Conti over 5 years

@Nakamura because INSERT is a query?
Vaibhav Vishal about 5 years

so .create() creates an object even if an required field(null=False) is missing? I am adding tests to my project and create is having unexpected results
Thomas Leonard about 5 years

No, it should not... Though some field types act a bit weird in Django. For example, CharField even if set to null=False will not raise an error if not provided: this is because Django set strings by default to an empty string "" so it is not technically null
Vaibhav Vishal about 5 years

yeah, I am having problems only with char fields and field field(which is basically char field too). Using obj = MyModel(), then obj.full_clean() for now.
Artur Barseghyan over 4 years

Josh Smeaton gave an excellent answer regarding developer own responsibility to cast types. Please, update your answer.
Martin Thoma almost 3 years

@madzohan I think the docs changed to the exact opposite: "To create an object, instantiate it using keyword arguments to the model class, then call save() to save it to the database."
Martin Thoma almost 3 years

It would be nice to point out what the difference between Model.objects.create(...) and obj = Model(); obj.save() is.
jcgoble3 about 2 years

This is much better and more helpful than the accepted answer.