Django Model（）与Model.objects.create（）

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?

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.

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")

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