Model মডেল

from django.db import models

class Post(models.Model):
    title = models.CharField(max_length=200)
    content = models.TextField()
    pub_date = models.DateTimeField(auto_now_add=True)
    author = models.ForeignKey('Author', on_delete=models.CASCADE)
    
    def __str__(self):
        return self.title

python manage.py makemigrations

python manage.py migrate

from django.core.validators import MaxLengthValidator, MinLengthValidator

class Book(models.Model):
    title = models.CharField(max_length=100, validators=[MaxLengthValidator(100), MinLengthValidator(5)])

from django.core.validators import EmailValidator

class Author(models.Model):
    email = models.EmailField(validators=[EmailValidator()])

from django.core.validators import RegexValidator
from django.db import models

class UserProfile(models.Model):
    phone_regex = RegexValidator(
        regex=r'^\+?1?\d{9,15}$',
        message="Phone number must be entered in the format: '+999999999'. Up to 15 digits allowed."
    )
    phone_number = models.CharField(validators=[phone_regex], max_length=17)

from django.core.validators import MinValueValidator, MaxValueValidator

class Rating(models.Model):
    stars = models.PositiveIntegerField(validators=[MinValueValidator(1), MaxValueValidator(5)])

from django.core.validators import DateValidator
from django.db import models

class Event(models.Model):
    date = models.DateField(validators=[DateValidator()])

from django.core.validators import URLValidator
from django.db import models

class Website(models.Model):
    url = models.URLField(validators=[URLValidator()])

from django.core.exceptions import ValidationError
class Item(models.Model):
    quantity = models.PositiveIntegerField(default=0)
    def clean(self):
        if self.quantity == 0:
            raise ValidationError("Quantity cannot be 0.")

from django.core.exceptions import ValidationError

def validate_even(value):
    if value % 2 != 0:
        raise ValidationError(
            _('%(value)s is not an even number'),
            params={'value': value},
        )

class EvenNumber(models.Model):
    number = models.IntegerField(validators=[validate_even])

from django.db import models
from django.core.validators import ValidationError
from django.utils.translation import gettext_lazy as _

def validate_unique_username(value):
    existing_users = User.objects.filter(username=value)
    if existing_users.exists():
        raise ValidationError(
            _('%(value)s already exists as a username.'),
            params={'value': value},
        )

class User(models.Model):
    username = models.CharField(
        max_length=30,
        unique=True,
        validators=[validate_unique_username],
    )

    def __str__(self):
        return self.username

from django.db import models

class Post(models.Model):
    title = models.CharField(max_length=200)
    content = models.TextField()
    pub_date = models.DateTimeField(auto_now_add=True)
    author = models.ForeignKey('Author', on_delete=models.CASCADE)
    
    class Meta:
        ordering = ['-pub_date']
        verbose_name = 'Blog Post'
        verbose_name_plural = 'Blog Posts'

from django.db import models

class Post(models.Model):
    title = models.CharField(max_length=200)
    content = models.TextField()
    pub_date = models.DateTimeField(auto_now_add=True)

from django.contrib import admin
from .models import Post

@admin.register(Post)
class PostAdmin(admin.ModelAdmin):
    list_display = ('title', 'author', 'pub_date')
    search_fields = ('title', 'author__name')  # Assuming Author model has a 'name' field
    list_filter = ('author',)
    ordering = ('-pub_date',)
    readonly_fields = ('pub_date',)
    

#models.py
class Post(models.Model):
    title = models.CharField(max_length=200, unique=True)
    slug = models.SlugField(max_length=200, unique=True)

#admin.py
from .models import  Post
class PostAdmin(admin.ModelAdmin):

    prepopulated_fields = {'slug': ('title',)}

admin.site.register(Post,PostAdmin)

from django.db import models

class CompanyInfoManager(models.Manager):
    def get_or_create_single(self, defaults=None, **kwargs):
        instance, created = self.get_or_create(**kwargs, defaults=defaults)
        return instance

class CompanyInfo(models.Model):
    name = models.CharField(max_length=100)
    address = models.TextField()
    # Add other fields as needed

    objects = CompanyInfoManager()

    def save(self, *args, **kwargs):
        # Ensure that only one instance exists
        if CompanyInfo.objects.exists() and not self.pk:
            raise ValueError("Only one CompanyInfo instance can be created.")
        super().save(*args, **kwargs)

    def delete(self, *args, **kwargs):
        # Prevent deletion of the instance
        pass

    class Meta:
        verbose_name_plural = "Company Information"
 

from django.contrib import admin
from .models import CompanyInfo

@admin.register(CompanyInfo)
class CompanyInfoAdmin(admin.ModelAdmin):
    # Define the fields to display and edit in the admin panel
    list_display = ('name', 'address')
    fields = ('name', 'address')
    # Disable the "Add" button in the admin panel
    def has_add_permission(self, request):
        return False