Django Model vs Model objects create

Question

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

User · Answer

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")

User · Answer

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     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    lt QuerySet    subject id   1   name    Math    max marks   50   gt    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        quot  quot  quot      Create a new object with the given kwargs  saving it to the database     and returning the created object       quot  quot  quot      obj   self model   kwargs      self  for write   True     obj save force insert True  using self db      return obj  For more details follow the links   https   docs djangoproject com en stable ref models querysets  create  https   github com django django blob 2d8dcba03aae200aaa103ec1e69f0a0038ec2f85 django db models query py L440

User · Answer

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

User · Answer

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

[python] Django Model() vs Model.objects.create()

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