how to make django model run some function when create

def model_created_or_updated(sender, ** kwargs):
   the_instance = kwargs['instance']
do_something()

post_save.connect(model_created_or_updated, sender = YourModel)

from django.db
import models

class Book(models.Model):
   title = models.CharField(max_length = 100)

@classmethod
def create(cls, title):
   book = cls(title = title)
# do something with the book
return book

book = Book.create("Pride and Prejudice")

class BookManager(models.Manager):
   def create_book(self, title):
   book = self.create(title = title)
# do something with the book
return book

class Book(models.Model):
   title = models.CharField(max_length = 100)

objects = BookManager()

book = Book.objects.create_book("Pride and Prejudice")

from django.db.models
import DEFERRED

@classmethod
def from_db(cls, db, field_names, values):
   # Default implementation of from_db()(subject to change and could # be replaced with super()).
if len(values) != len(cls._meta.concrete_fields):
   values = list(values)
values.reverse()
values = [
   values.pop() if f.attname in field_names
   else DEFERRED
   for f in cls._meta.concrete_fields
]
instance = cls( * values)
instance._state.adding = False
instance._state.db = db
# customization to store the original field values on the instance
instance._loaded_values = dict(
   zip(field_names, (value
      for value in values
      if value is not DEFERRED))
)
return instance

def save(self, * args, ** kwargs):
   # Check how the current values differ from._loaded_values.For example,
   # prevent changing the creator_id of the model.(This example doesn 't
      # support cases where 'creator_id'
      is deferred).
if not self._state.adding and(
      self.creator_id != self._loaded_values['creator_id']):
   raise ValueError("Updating the value of creator isn't allowed")
super().save( * args, ** kwargs)

>>> obj = MyModel.objects.first() >>>
   del obj.field >>>
   obj.field # Loads the field from the database

def test_update_result(self):
   obj = MyModel.objects.create(val = 1)
MyModel.objects.filter(pk = obj.pk).update(val = F('val') + 1)
# At this point obj.val is still 1, but the value in the database
# was updated to 2. The object 's updated value needs to be reloaded
# from the database.
obj.refresh_from_db()
self.assertEqual(obj.val, 2)

class ExampleModel(models.Model):
   def refresh_from_db(self, using = None, fields = None, ** kwargs):
   # fields contains the name of the deferred field to be
# loaded.
if fields is not None:
   fields = set(fields)
deferred_fields = self.get_deferred_fields()
# If any deferred field is going to be loaded
if fields.intersection(deferred_fields):
   # then load all of them
fields = fields.union(deferred_fields)
super().refresh_from_db(using, fields, ** kwargs)

from django.db
import models
from django.urls
import reverse

class MyModelName(models.Model):
   ""
"A typical class defining a model, derived from the Model class."
""

# Fields
my_field_name = models.CharField(max_length = 20, help_text = 'Enter field documentation')
#…

# Metadata
class Meta:
   ordering = ['-my_field_name']

# Methods
def get_absolute_url(self):
   ""
"Returns the URL to access a particular instance of MyModelName."
""
return reverse('model-detail-view', args = [str(self.id)])

def __str__(self):
   ""
"String for representing the MyModelName object (in Admin site etc.)."
""
return self.my_field_name

my_field_name = models.CharField(max_length = 20, help_text = 'Enter field documentation')

class CatalogConfig(AppConfig):
   default_auto_field = 'django.db.models.BigAutoField'

class Meta:
   ordering = ['-my_field_name']

ordering = ['title', '-pubdate']

verbose_name = 'BetterName'

pip install pipenv
pipenv shell
pipenv install django

django - admin startproject crud. /

   python manage.py startapp codebase

python manage.py migrate

python manage.py runserver

INSTALLED_APPS = [
   'django.contrib.admin',
   'django.contrib.auth',
   'django.contrib.contenttypes',
   'django.contrib.sessions',
   'django.contrib.messages',
   'django.contrib.staticfiles',

   'codebase'
]

from django.db
import models
from django.urls
import reverse

class CRUD(models.Model):
   name = models.CharField(max_length = 30)
age = models.IntegerField()
level = models.CharField(max_length = 30)
date = models.DateTimeField(auto_now_add = True)

#display the data with name
def __str__(self):
   return self.name

from django.contrib
import admin
from.models
import CRUD

admin.site.register(CRUD)

from django
import forms
from.models
import CRUD

class CRUDFORM(forms.ModelForm):
   name = forms.CharField(widget = forms.TextInput(attrs = {
      "class": "form-control",
      "placeholder": "name"
   }))
age = forms.CharField(widget = forms.TextInput(attrs = {
   'type': "number",
   "class": "form-control",
   "placeholder": "age"
}))

level = forms.CharField(widget = forms.TextInput(attrs = {
   "class": "form-control",
   "placeholder": "level"
}))
class Meta:
   model = CRUD
fields = [
   'name', 'age', 'level'
]

from django.shortcuts
import redirect, render, get_object_or_404
from.models
import CRUD
from.forms
import CRUDFORM

def home(request):
   queryset = CRUD.objects.all().order_by('-date')
context = {
   'queryset': queryset
}
return render(request, 'app/base.html', context)

def create(request):
   form = CRUDFORM(request.POST or None)

if request.method == "POST":
   if form.is_valid():
   form.save()
return redirect('home')
context = {
   "form": form
}
return render(request, 'app/createform.html', context)

def model_created_or_updated(sender, ** kwargs):
   the_instance = kwargs['instance']
do_something()

post_save.connect(model_created_or_updated, sender = YourModel)

>>> from events.models import Venue
>>> Venue.objects.exclude(name="South Stadium")
<QuerySet [<Venue: West Park>, <Venue: North Stadium>, <Venue: East Park>]>

>>> from events.models import Event
>>> from datetime import datetime, timezone
>>> venue1 = Venue.objects.get(name="East Park")
>>> Event.objects.exclude(venue=venue1,event_date=datetime(2020,23,5,tzinfo=timezone.utc))
<QuerySet [<Event: Test Event>, <Event: Club Presentation - Juniors>, <Event: Club Presentation - Seniors>, <Event: Gala Day>]>

>>> from events.models
import Event
   >>>
   from django.db.models
import Count
   >>>
   qry = Event.objects.annotate(total_attendees = Count('attendees')) >>>
   for event in qry:
   ...print(event.name, event.total_attendees)
   ...
   Test Event 0
Gala Day 2
Club Presentation - Juniors 5
Club Presentation - Seniors 3 >>>

>>> Event.objects.all().order_by('event_date','name')
<QuerySet [<Event: Club Presentation - Juniors>, <Event: Club Presentation - Seniors>, <Event: Gala Day>, <Event: Test Event>]>

>>> Event.objects.all().order_by('-name')
<QuerySet [<Event: Test Event>, <Event: Gala Day>, <Event: Club Presentation - Seniors>, <Event: Club Presentation - Juniors>]>