CODEWITHSUNDEEP
pythondjangodjango-modelsdjango-related-manager
darkhorse
darkhorse

Reputation: 8742

Object needs to have a value for field "id" before this many-to-many relationship can be used in Django

I have the following code in my models.py:

class Tag(models.Model):
    name = models.CharField(max_length=75)

class Article(models.Model):
    tags = models.ManyToManyField(Tag)

    def save(self, *args, **kwargs):
        for tag in self.tags:
            print tag.name
        super(Article, self).save(*args, **kwargs)

When I try to create an article from the admin panel, I get the following error:

ValueError: "<Article>" needs to have a value for field "id" before this many-to-many relationship can be used.

How can I fix this problem? I need to access and iterate the tags before saving the article. Thanks!

Upvotes: 9

Views: 8199

Answers (2)

aircraft
aircraft

Reputation: 26914

Your models are bellow:

class Tag(models.Model):
    name = models.CharField(max_length=75)

class Article(models.Model):
    tags = models.ManyToManyField(Tag)

    def save(self, *args, **kwargs):
        for tag in self.tags:
            print tag.name
        super(Article, self).save(*args, **kwargs)

when you want to create a Article instance with tags, you should create the instance firstly, then add the tags, like bellow:

article = Article.objects.create()

tags = [tag_instance1, tag_instance2, tag_instance3 ...]

article.tags.set(tags)

or 

article.tags.add(tag_instance)

Upvotes: 1

Aditya R
Aditya R

Reputation: 39

Your Declaration of

form.save_m2m()

should be after 

obj.save()

After saving of object Many to Many field will add

Upvotes: 3

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