Django Model: many-to-many or many-to-one?

Question

I'm just learning django and following a tutorial. I have a Link and a Bookmark. Unlike the tutorial I'm following, I would like a link to be associated with only one Bookmark, but a Bookmark can have multiple links. Is this the way to setup the model?

class Link(models.Model):
    url = models.URLField(unique=True)
    bookmark = models.ForeignKey(Bookmark)

class Bookmark(models.Model):
    title = models.CharField(maxlength=200)
    user = models.ForeignKey(User)
    links = models.ManyToManyField(Link)

Answer 1

No. Remove links from the Bookmark model, and to access the Link objects for a specific Bookmark you will use bookmark.link_set.all() (where bookmark is a specific Bookmark object). Django populates the reverse relationship for you.

Or if you so choose, provide your own related name in the bookmark ForeignKey, such as "links" if you do not like "link_set".

Answer 2

It's enough to define the relationship in one of the models. Django will automatically create an attribute in the other model.

If you want a link to be associated with only one bookmark, define a foreign key in Link that refers back to a Bookmark object:

class Bookmark(models.Model):
    title = models.CharField(max_length=200)
    user = models.ForeignKey(User)

class Link(models.Model):
    url = models.URLField(unique=True)
    bookmark = models.ForeignKey(Bookmark)

To access the links of a bookmark, use bookmark.link_set. This attribute is automatically created by Django.

Answer 3

No, remove the links = statement from Bookmark -- what's predefined for you in bookmark is a property link_set that's the query for the links whose bookmark is this one (you can rename that property, but there's really no need).