ruby on rails - Using scope to calculate SUM from two tables -

ruby on rails - Using scope to calculate SUM from two tables -

i have 2 db tables next fields:

log_lines: id, user_id, date fragments: id, log_line_id, amount

corresponding models:

models/log_lines.rb

class logline < activerecord::base has_many :fragments, dependent: :destroy def total_amount fragments.sum(:amount) end end

models/fragments.rb

class fragment < activerecord::base belongs_to :log_line end

i want amount sum depending user_id. sql query job:

select sum(f.amount) log_lines ll left bring together fragments f on f.log_line_id = ll.id ll.user_id = 74123;

i've created total_amount method in logline model , calling logline controller:

amount = 0 ll_list = logline.where(:user_id => user_id) ll_list.each { |ll| amount += ll.total_amount }

actually works, think not efficient way implement it. because many database queries executed during such collection of data.

would possible implement via 1 scope?

this possible via 1 scope. use:

class logline < activerecord::base scope :user_amount, ->(user_id) { select('sum(fragments.amount') .joins('left bring together fragments on fragments.log_line_id = log_line.id') .where('log_line.user_id = ?', user_id) } end

another way it:

class logline < activerecord::base scope :user_amount, ->(user_id) { joins('left bring together fragments on fragments.log_line_id = log_line.id') .where(fragments: { user_id: user_id }) .sum('fragments.amount') } end

ruby-on-rails ruby-on-rails-4