Question

I have a form that is used to record a transaction. Liquid is moved from one tank to another. My form takes the from tank and the to tank and the number of gallons transferred. i would like this to be entered into the database as two rows. The first would be the from Tank ID and a negative number and the second row would be the to Tank ID and a positive number.

Example:
Transferring 36 gallons from Tank 1 to Tank 2

    id   | tank_id | tran_amount
   ------------------------------
     1   |    1    |     -36
     2   |    2    |      36

This is something that I would have achieved with ease writing SQL code in PHP but I am at a loss in Rails. How can I do this from one form?

Answer 1

Something seems missing in your database model here, don’t you want something to tie the transfer together? I would do:

id | from_tank_id | to_tank_id | transfer_amount

If you are stuck with the existing model, which assume is in a model called Transfer, there is nothing that prevents you from creating two in the controller, just put them in a transaction.

#in TransferController.create
amount = params[:amount].to_i
Transfer.transaction do
  Transfer.create(:tank_id => params[:from_tank_id], :tran_amount => -amount)
  Transfer.create(:tank_id => params[:to_tank_id], :tran_amount => amount)
end