Module: SimilarModels

Defined in:
lib/similar_models.rb,
lib/similar_models/version.rb

Constant Summary collapse

VERSION = 
'0.4.1'

Class Method Summary collapse

Instance Method Summary collapse

Class Method Details

.join_table_values(many_to_many_assocation) ⇒ Object 



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# File 'lib/similar_models.rb', line 97

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

Instance Method Details

#has_similar_models(*many_to_many_associations, as: nil) ⇒ Object 



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# File 'lib/similar_models.rb', line 5

def has_similar_models(*many_to_many_associations, as: nil)
  as ||= "similar_#{model_name.plural}"

  # example sql query for one many to many association:
  #
  # SELECT posts.*,
  #   (select count(*) from author_posts where post_id != posts.alt_id and author_id in
  #     (select author_id from author_posts where post_id = posts.alt_id)) AS similar_posts_commonality_count
  #   FROM "posts"
  #   ORDER BY similar_posts_commonality_count DESC, created_at DESC
  #
  define_singleton_method as do
    primary_key_ref = "#{table_name}.#{primary_key}"
    similarity_counts = []

    many_to_many_associations.each do |many_to_many_association|
      association = reflect_on_association(many_to_many_association)
      join_table, foreign_key, association_foreign_key = join_table_values(association)

      similarity_counts <<
        "(select count(*) from #{join_table} where #{foreign_key} != #{primary_key_ref} and " \
        "#{association_foreign_key} in " \
        "(select #{association_foreign_key} from #{join_table} where #{foreign_key} = #{primary_key_ref}))"
    end

    order_clause = "#{as}_commonality_count DESC"
    order_clause += ", created_at DESC" if column_names.include?('created_at')
    select("#{table_name}.*, #{similarity_counts.join(' + ')} AS #{as}_commonality_count").order(order_clause)
  end

  # example sql query for one many to many association:
  #
  # SELECT posts.*, count(posts.alt_id) AS similar_posts_commonality_count
  #   FROM "posts"
  #   INNER JOIN author_posts ON author_posts.post_id = posts.alt_id
  #     WHERE "posts"."alt_id" != ? AND
  #       author_posts.author_id IN (select author_posts.author_id from author_posts where author_posts.post_id = ?)
  #   GROUP BY posts.alt_id
  #   ORDER BY similar_posts_commonality_count DESC, created_at DESC
  #
  # example sql query for two many to many associations:
  #
  # SELECT posts.*, count(posts.alt_id) AS similar_posts_by_author_and_tag_commonality_count
  #   FROM (
  #     (SELECT "posts".* FROM "posts"
  #       INNER JOIN author_posts ON author_posts.post_id = posts.alt_id
  #       WHERE (author_posts.author_id IN
  #         (select author_posts.author_id from author_posts where author_posts.post_id = ?)
  #       )
  #     )
  #   UNION ALL
  #     (SELECT "posts".* FROM "posts"
  #       INNER JOIN posts_tags ON posts_tags.post_id = posts.alt_id
  #       WHERE (posts_tags.tag_id IN
  #         (select posts_tags.tag_id from posts_tags where posts_tags.post_id = ?)
  #       )
  #     )
  #   )
  #   AS posts WHERE "posts"."alt_id" != ? GROUP BY posts.alt_id, posts.created_at, posts.updated_at
  #   ORDER BY similar_posts_by_author_and_tag_commonality_count DESC, created_at DESC
  #
  define_method as do
    table_name = self.class.table_name
    primary_key = self.class.primary_key
    primary_key_ref = "#{table_name}.#{primary_key}"
    association_scopes = []

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

      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} = #{primary_key_ref}")
    end

    order_clause = "#{as}_commonality_count DESC"
    order_clause += ", created_at DESC" if self.class.column_names.include?('created_at')
    scope = self.class.select("#{table_name}.*, count(#{primary_key_ref}) AS #{as}_commonality_count").
      where.not(primary_key => self.id).order(order_clause)

    # 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(primary_key_ref)
    else
      group_by_clause = self.class.column_names.map { |column| "#{table_name}.#{column}"}.join(', ')
      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