How to Find the Top N Most Associated Records in Rails 3 using has_many?

Ordering Records by Association Count in Rails 3 ActiveRecord

In Rails 3, you can utilize the has_many association to effectively determine the most popular records based on association counts. Consider the example of a Song model with an associated Listen model, where each Listen belongs to a Song.

To retrieve the top 5 most listened to songs, you can define a scope within the Song model using named scopes:

class Song
  has_many :listens
  scope :top5,
    select("songs.id, OTHER_ATTRS_YOU_NEED, count(listens.id) AS listens_count").
    joins(:listens).
    group("songs.id").
    order("listens_count DESC").
    limit(5)
end

This scope combines the power of named scopes and associations. It calculates the listen count for each song, sorts the results in descending order based on that count, and limits the result set to the top 5 most listened songs.

By leveraging the top5 scope, you can conveniently obtain the most popular songs using a simple query:

Song.top5 # top 5 most listened songs

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