oop - Whats the difference between models and models.Model in django?(and similarly for forms and forms.Form ) - Stack Overflow
python - what does " models.Model "mean - Stack Overflow
ELI5: Django Models and Model Methods?
python - Django Model() vs Model.objects.create() - Stack Overflow
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How do Django model fields work?
To use methods such as save(), create(), delete(), etc from Model class
As you say, models is a package, that is, a set of classes / methods. For convenience, models and forms are imported only once and the classes they contain are used. Example: models.CharField, otherwise you would have to import the classes one by one (unnecessarily).
Model is a class to create entities in your database.
It means: make the Poll class inherit from the Model base class from the models module.
Do you know what inheritance is? I would start by looking at some examples:
http://parand.com/say/index.php/2009/04/20/python-simple-inheritance-example/
It is basically saying to use all the properties that the Model class has plus whatever you define on your class.
Good luck
in php that would be:
class Poll extends Model
{
var $question;
var $pub_date;
}
Model is a class that is in the models module in Django framework...
My understanding so far is, the Django models is used to create the actual columns for the database.
Once I have declared the columns. What is the methods that follow it ? The documentation says this:
Define custom methods on a model to add custom “row-level” functionality to your objects. Whereas Manager methods are intended to do “table-wide” things, model methods should act on a particular model instance.
This is a valuable technique for keeping business logic in one place – the model.
ELI5?
I'm trying to create a comments section using React JS, this is the model I have so far:
class Comment(models.Model):
show = models.CharField(max_length=25)
username = models.CharField(max_length=16)
comment = models.TextField(max_length=1000)
time_stamp = models.DateTimeField()
What kind of methods would be relevant?
Also, I understand that Django comes default with sqlite3. If I was to go into settings.py and change the database to MySQL, would my models create the columns in MySQL instead? And would the backend admin page login take me to the MySQL 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 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, whileModel.objects.create()does only INSERT.Model.save()doesUPDATE If the object’s primary key attribute is set to a value that evaluates to
TrueINSERT 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, butModel.objects.create()raisesIntegrityError.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() <QuerySet [{'subject_id': 1, 'name': 'Math', 'max_marks': 50}]>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 (changesnamefrom Physics to Math, andmax_marksfrom 100 to 50), becausesubject_idis a primary key andsubject_id=1already exists in the DB. ButSubject.objects.create()raisesIntegrityError, because, again the primary keysubject_idwith the value1already exists.
Forced insert
Model.save()can be made to behave asModel.objects.create()by usingforce_insert=Trueparameter:Model.save(force_insert=True).
Return value
Model.save()returnNonewhereModel.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:
https://docs.djangoproject.com/en/stable/ref/models/querysets/#create
https://github.com/django/django/blob/2d8dcba03aae200aaa103ec1e69f0a0038ec2f85/django/db/models/query.py#L440