CODEWITHSUNDEEP
djangodatabase
flice com
flice com

Reputation: 125

Django Databases: Many to Many of a foregin key in a HASHTAG - FOLLOWER relation

Let's think I build Instagram platform.

**I need to lookup fast

I have 2 models:

class Follower():
   hastags = ???

class Hashtag():
    name = char...

ABILITY:

To be able to fetch -all specific follower- hashtags.

And reverse: fetch -all Followers- of a specific hastags.

NOTES:

A Follower don't have to have an hashtag.

An Hashtag exist only once a follower is adding it.

I think I can put a foreginKey on Hashtag instead of Follower but this seems to be messy since I mostly deal with the followers not the hashtags. I know I can add a funtion to add hashtag to follower in the follower model.

So best option is to use ManyToMany from Followers to Hashtags ? correct me if I am wrong ?

EXAMPLE:

Follower1 uses Hashtags: Tag1, Tag2

Follower2 uses Hashtags: Tag2, Tag3

Upvotes: 1

Views: 77

Answers (1)

AKX
AKX

Reputation: 169085

Yes, you'd use a many-to-many field.

class Follower(models.Model):
   followed_hashtags = models.ManyToManyField('Hashtag', related_name='followers')

To get all of the hashtags followed by someone, you can use the forward descriptor

hashtags = follower.followed_hashtags.all()

To get all of the followers for a hashtag, you can use the reverse descriptor

cat_hashtag = Hashtag.objects.get(name='cat')
cat_followers = cat_hashtag.followers.all()

You can also use the implicitly generated through table/model for even more interesting lookups, such as summaries of follow counts:

HashtagFollows = Follower.followed_hashtags.through
counts = HashtagFollows.objects.all().values('hashtag__name').annotate(count=Count())

This implicit table can also be used for lookups if you only have e.g. a follower ID:

follower_8s_hashtag_names = HashtagFollows.objects.filter(follower_id=8).values_list('hashtag__name')

And, if you need to e.g. store when a given Follower started following a hashtag, see extra-fields-on-many-to-many-relationships (which then replaces the implicit through table).

Upvotes: 2

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