module MostRelated

Constants

VERSION

Public Class Methods

join_table_values(many_to_many_assocation) click to toggle source

# File lib/most_related.rb, line 76
def self.join_table_values(many_to_many_assocation)
  if many_to_many_assocation.macro == :has_and_belongs_to_many
    join_table = many_to_many_assocation.join_table
    foreign_key = many_to_many_assocation.foreign_key
    association_foreign_key = many_to_many_assocation.association_foreign_key
  elsif many_to_many_assocation.macro == :has_many
    join_table = many_to_many_assocation.through_reflection.table_name
    foreign_key = many_to_many_assocation.through_reflection.foreign_key
    association_foreign_key = many_to_many_assocation.foreign_key
  end
  [join_table, foreign_key, association_foreign_key]
end

Public Instance Methods

has_most_related(*many_to_many_associations, as: :most_related) click to toggle source

`most_related` returns those models that have the most

associated models in common

Post example:

class Post < ActiveRecord::Base
  has_most_related :authors
  has_most_related :tags, as: :most_related_by_tags
  has_most_related :authors, :tags, as: :most_related_by_author_or_tag

  has_many :author_posts
  has_many :authors, through: :author_posts
end

class Author < ActiveRecord::Base
  has_many :author_posts
end

class AuthorPosts < ActiveRecord::Base
  belongs_to :author
  belongs_to :post
end

To return the posts with the most authors in common with `post`, in descending order:

post.most_related

To return the posts with the most tags in common with `post`, in descending order:

post.most_related_by_tag

To return the posts with the most authors and tags in common with `post`, in descending order:

post.most_related_by_author_or_tag

The count of the associated models in common is accessible on each returned model

eg post.most_related_count, post.most_related_by_tag_count and post.most_related_by_author_or_tag_count

# File lib/most_related.rb, line 40
def has_most_related(*many_to_many_associations, as: :most_related)

  # defaults to 'def most_related'
  define_method as do
    table_name = self.class.table_name
    association_scopes = []

    many_to_many_associations.each do |many_to_many_association|
      assocation = self.class.reflect_on_association(many_to_many_association)
      join_table, foreign_key, association_foreign_key = self.class.join_table_values(assocation)

      association_scopes << self.class.where("#{join_table}.#{association_foreign_key} IN " +
        "(select #{join_table}.#{association_foreign_key} from #{join_table} " +
        "where #{join_table}.#{foreign_key} = :foreign_key)", foreign_key: self.id).
        joins("INNER JOIN #{join_table} ON #{join_table}.#{foreign_key} = #{table_name}.id")
    end

    scope = self.class.select("#{table_name}.*, count(#{table_name}.id) AS #{as}_count").
      where.not(id: self.id).order("#{as}_count DESC")
    group_by_clause = 'id'

    # if there is only one many-to-many association no need to use UNION sql syntax
    if association_scopes.one?
      scope.merge(association_scopes.first).group(group_by_clause)
    else
      # with postgres the group by clause has to be different
      # http://dba.stackexchange.com/questions/88988/postgres-error-column-must-appear-in-the-group-by-clause-or-be-used-in-an-aggre
      if ActiveRecord::Base.connection.adapter_name == 'PostgreSQL'
        group_by_clause = self.class.column_names.join(', ')
      end

      # see http://blog.ubersense.com/2013/09/27/tech-talk-unioning-scoped-queries-in-rails/
      scope.from("((#{association_scopes.map(&:to_sql).join(') UNION ALL (')})) AS #{table_name}").group(group_by_clause)
    end
  end

  def self.join_table_values(many_to_many_assocation)
    if many_to_many_assocation.macro == :has_and_belongs_to_many
      join_table = many_to_many_assocation.join_table
      foreign_key = many_to_many_assocation.foreign_key
      association_foreign_key = many_to_many_assocation.association_foreign_key
    elsif many_to_many_assocation.macro == :has_many
      join_table = many_to_many_assocation.through_reflection.table_name
      foreign_key = many_to_many_assocation.through_reflection.foreign_key
      association_foreign_key = many_to_many_assocation.foreign_key
    end
    [join_table, foreign_key, association_foreign_key]
  end
end