如何创建/保存此数据库特殊计算字段-RoR

Question

I have a database field called sample_code . This field is composed on the following way: sample_id/year/lab_id

The lab_id is fixed, always the same. The year changes accordingly to the current year... The sample_id its incremental (resetting every year and not a database field).

What I want to do is every-time I create a new sample it generates this sample_code for me and saves it along with the rest of the sample fields...

My doubts are: 1 - How can I keep incrementing sample_id if it's not on the database? 2 - How can I reset the sample ID code each year? 3 - Where's the best place to put/call this code? Sample's controller?

Thanks for all the help you can give

Answer 1

If you're not using your database outside of your app, it should be fine to just store the sample_id as its own column. You can then put a method on your model that returns something like:

def sample_code
  "#{sample_id}/#{Time.now.year}/<lab_id>"
end

Then you can just increment sample_id each time.

EDIT

Since you need to reset the id to 1 each year and the model is called Sample , you should avoid confusion by calling it something like annual_id instead of sample_id . sample_id would likely be confused with sample.id , which is a completely different thing.

With that change, you should just store the info in three columns on the model to make it easy: annual_id , year , and lab_id . Then for each record you can set:

annual_id = Sample.where(year: Time.now.year).pluck(:annual_id).max.to_i + 1
year = Time.now.year
lab_id = <however you are defining this>

This will use the current year for year and then reset the annual_id to 1 when there are no records because the year has changed (new year will give nil.to_i + 1 => 1 ).

Then you can just return the format you want for any given data point:

def sample_code
  "#{annual_id}/#{year}/#{lab_id}"
end