Get list of values from grandchildren records - django

Question

I'm trying to access the grandchildren records in a list to avoid duplicate records. In this example, a tag can only be used once across articles for a given author. I will use the resulting list of grandchildren records in my clean function to return validation errors.
class Article(models.Model):
tag = models.ManyToManyField(Tag)
author = models.ForeignKey(Author, on_delete=models.CASCADE)
class Tag(models.Model):
class Author(models.Model):
Right now I can do this:
print(author.articles.first().tag.first())
Travel
I'd like to be able to use something like author.articles.tags.all() to return the list and check the submitted form against it to raise a ValidationError message to the user.
How can this be done efficiently with the basic Many-to-Many setup without creating an intermediate table for the tag relationships? This is solely in the Admin interface, in case that matters at all.

Answer 1

i come from the link you posted on upwork,
the way i understand your question,
what you want to achieve seems to be impossible ,
what i think can work , is to fetch articles related to the author, with their corresponding tags,
after that they are retrieved you do filtering and remove duplicates.
otherwise the tag has nothing to connect it with the author,,

Answer 2

I'm so jealous that's a great answer #since9teen94
Be aware, I will not base my answer in the easiest solution but how we model reality (or how we should do it).
We put tags after things exists right?
In that order I will make your life horrible with something like this:
from django.db import models
class Author(models.Model):
name = models.CharField(max_length=30, null=False)
class Article(models.Model):
name = models.CharField(max_length=30, null=False)
author = models.ForeignKey(Author, on_delete=models.CASCADE)
class Tag(models.Model):
name = models.CharField(max_length=30, null=False, unique=True)
articles = models.ManyToManyField(Article)
but believe me you don't want to follow this approach it will make your work harder.
You can search for Articles based on Tags directly
Tag.objects.filter(name='Scify').first().articles.all() # name is unique
The real issue with this is that the reverse lookup is really complex (I mean.. get ready for debug)
Article.objects.filter(
id__in=list(
Tag.objects.filter(name='Scify').first().articles.values_list('id', flat=True)
)
)
I am sure this does not solve your problem and I don't like complex code for no reason but if you're open to suggestions I don't mind to think different and add some options
Edit:
About the author and clean repeated tags.. well you don't have to deal with that and if you want to find all Tag your author has you could loop the tags
for tag in Tag.objects.all():
if tag.articles.filter(author__name='StackoverflowContributor'):
print(tag.name)
# > Scify
I am just saying that there are options not that this is the best for you but don't be afraid of the terminal, it's really cool

Answer 3

The Django ORM is pretty cool when you get used to it, but regular SQL is pretty cool too
# created_at, updated_at, name and tag_val are variables I
# added due to my slight ocd lol
class Author(models.Model):
name = models.CharField(max_length=255)
created_at = models.DateTimeField(auto_now_add=True)
updated_at = models.DateTimeField(auto_now=True)
class Tag(models.Model):
tag_val = models.CharField(max_length=255)
created_at = models.DateTimeField(auto_now_add=True)
updated_at = models.DateTimeField(auto_now=True)
class Article(models.Model):
author = models.ForeignKey(Author,related_name='articles', on_delete=models.CASCADE)
tags = models.ManyToManyField(Tag, related_name='articles')
created_at = models.DateTimeField(auto_now_add=True)
updated_at = models.DateTimeField(auto_now=True)
I can write my query like this, assuming the variable 'author' has been assigned an Author object instance, and get a list of dictionaries [{'tags':1},{'tags':2}] where the value is the auto generated primary key id of the Tag object instance
author.articles.values('tags').distinct()