唯一约束失败：django 中的 post_author.href

Question

I will create a different author table using the user table available in django and I want to combine this custom table I created with the column in the post model. Thus, I will have both the author table and the post table with the posts shared by these authors separately. And also, I will make the user models that I will create in the future with the ready user table. but I am getting the error I mentioned. When i add authors to admin panel I get this error. When I add 1 author, there is no problem, but when I add 2nd author, I get this error. How can I solve this, what are the alternative ways?

from django.db import models
from django.contrib.contenttypes.models import ContentType
from django.db import models
from django.urls import reverse
from .utils import get_read_time
from django.conf import settings
from django.utils import timezone
from markdown_deux import markdown
from django.utils.text import slugify
from django.contrib.auth.models import User
from django.db.models.signals import pre_save
from django.utils.safestring import mark_safe

class GENDER(models.TextChoices):

    Erkek = "Erkek"
    Kadın = "Kadın"
    Diğer = "Diğer"
    NONE = "Belirtmek İstemiyorum"


class Category_Choices(models.TextChoices):
    BİLİNMEYENLER = '13İlinmeyenler'
    KİŞİSEL_GELİŞİM = 'Kişisel Gelişim'
    İLHAM_AL = 'İlham Al'
    YATIRIM_HABERLERİ = 'Yatırım Haberleri'
    GİRİŞİMCİLİK = 'Girişimcilik'
    ENGLİSH_NEWS = 'English News'
    BAŞARI_HİKAYELERİ = "Başarı Hikayeleri"


class Color_Choices(models.TextChoices):
    INDIGO = 'indigo'
    green = 'green'
    yellow = 'yellow'
    RED = 'red'
    blue = 'blue'
    gray = 'gray'
    pink = "pink"



class Author(models.Model):

    author = models.ForeignKey(User, on_delete = models.CASCADE)
    firstName = models.CharField(max_length=80)
    lastName = models.CharField(max_length=80)
    email = models.EmailField(null=True,blank=True)
    displayName = models.CharField(max_length=100)
    gender = models.TextField(blank=False,choices=GENDER.choices)
    avatar = models.ImageField(upload_to="avatar")
    href = models.SlugField(unique=True,editable=False)
    desc = models.TextField()
    jobName = models.CharField(default="Yazar",max_length=30)
    bgImage = models.ImageField(null=True, blank=True, upload_to="background")

    def __str__(self):
        return self.displayName

    def get_slug(self):
        href = slugify(self.displayName.replace("ı","i"))
        unique = href
        number = 1

        while Author.objects.filter(slug=unique).exists():
            unique = "{}-{}" .format(href,number)
            number += 1

        return unique




class Categories(models.Model):

    name = models.CharField(max_length=50,choices=Category_Choices.choices,default=Category_Choices.BİLİNMEYENLER)
    color = models.CharField(max_length=30,choices=Color_Choices.choices, default=Color_Choices.RED)
    href = models.SlugField(unique=True,editable=False)
    thumbnail = models.ImageField(upload_to="postpost",null=True,blank=True)

    def __str__(self):
        return self.name

    def get_category_slug(self):
        slug = slugify(self.name.replace("ı","i"))
        unique = slug
        number = 1

        while Categories.objects.filter(slug=unique).exists():
            unique = "{}-{}" .format(slug,number)
            number += 1

        return unique
    def save(self, *args, **kwargs):
        self.href = slugify(self.name)
        super(Categories,self).save(*args, **kwargs)

    def get_absolute_url(self):
        return self.href

class Post(models.Model):

    authorId = models.ManyToManyField(Author)
    title = models.CharField(max_length=255)
    desc = models.CharField(max_length=255)
    categoryID = models.ForeignKey(Categories,on_delete=models.CASCADE,)
    content = models.TextField(blank=False)
    href = models.SlugField(unique=True,editable=False)
    draft = models.BooleanField(default=True)
    readingtime = models.IntegerField(default=0)
    updated = models.DateTimeField()
    date = models.DateTimeField(editable=False,null=True)
    published = models.DateField(default=timezone.now)
    featuredimage = models.ImageField(null=True, blank=True, upload_to='post')




    class Meta:
        ordering = ['-date', '-updated']

    def __str__(self):
        return self.title

    def get_slug(self):
        slug = slugify(self.title.replace("ı","i"))
        unique = slug
        number = 1

        while Post.objects.filter(slug=unique).exists():
            unique = "{}-{}" .format(slug,number)
            number += 1

        return unique
    #@property
    #def comments(self):
    #    instance = self
    #    qs = Comment.objects.filter_by_instance(instance)
    #    return qs


    def get_markdown(self):
        content = self.content
        markdown_text = markdown(content)
        return mark_safe(markdown_text)


def pre_save_receiver(sender, instance, *args, **kwargs):
    if not instance.href and instance.title:
        instance.href = slugify(instance.title)
    if instance.content:
        html_string = instance.get_markdown()
        read_time_var = get_read_time(html_string)
        instance.read_time = read_time_var






pre_save.connect(pre_save_receiver, sender=Post)

and this error

IntegrityError at /adminpost/author/add/
UNIQUE constraint failed: post_author.href
Request Method: POST
Request URL:    http://127.0.0.1:8000/adminpost/author/add/
Django Version: 3.2.8
Exception Type: IntegrityError
Exception Value:    
UNIQUE constraint failed: post_author.href

Answer 1

It seems that you try to make a create with a title that already exists. Thus your href field isn't unique anymore.

Either also make the title field unique or you can add some random number identifier to your slug.

import uuid

def pre_save_receiver(sender, instance, *args, **kwargs):
    if not instance.href and instance.title:
        if not Post.objects.filter(href=slugify(instance.title)).exists():
            instance.href = slugify(instance.title)
        else:
            instance.href = slugify(instance.title) + str(uuid.uuid4())[:8]