Rails：在构建对象时/保存对象之前检查是否存在符合特定条件的关联？

Question

I have a model called Timesheet which has many TimesheetRows. TimesheetRow belongs to a job.

class Timesheet < ActiveRecord::Base
  has_many :timesheet_rows, inverse_of: timesheet
end
class TimesheetRow < ActiveRecord::Base
  belongs_to :timesheet, inverse_of: timesheet_rows
  belongs_to :job
end

While building a timesheet object from logs, I am trying to check if timesheet_row corresponding to a job has been already built or not, as follows.

timesheet = Timesheet.new()

if timesheet.timesheet_rows.exists?(job_id:n)
  #Do something
else 
  timesheet.timesheet_rows.build(job_id:n)
end

I have tried .exists?(condition) , .find(:all, condition) , .find_by_job_id(n) , .where(condition) etc. All query from database, and thus won't be useful here.

I have browsed for hours now, looking for some magic method but couldn't find any. Really, will I just have to loop through all the associations?

A similar question .

Thanks

Answer 1

Try using ruby's select method, and then checking if the resulting array is empty.

if timesheet.timesheet_rows.select { |tr| tr.job_id == n }.empty?
  timesheet.timesheet_rows.build(job_id: n)
else 
  # Do something
end

As @Bot suggested in the comments, you can also use the any? rather than select and empty? .

if timesheet.timesheet_rows.any? { |tr| tr.job_id == n }
  # Do something
else 
  timesheet.timesheet_rows.build(job_id: n)
end