Question

We have following code in our out_logs controller for saving into two tables in rails 3.1.3 app. In order to make sure the two savings are done with completion or none, a transaction is used.

  @out_log.transaction do
    if @out_log.save && @part.save
      redirect_to part_path(@part), :notice => "Saved！"
    else
      flash.now[:error] = "Not saved！"
      render 'new'
    end   
  end  

The code seems working. Our questions are:

1. Is the code above good practice for transaction?
2. There are redirect_to and render in transaction loop, will these redirect_to or render increase the execution time for transaction loop and therefore will lock the database (we use sqlite3) for too long?

Thanks so much.

Answer 1

First off: redirect_to or render don’t act like a return statement. They just assign some headers in a response that is currently being prepared.

About transactions:

if @out_log.save && @part.save

The above code is sure to lead to inconsistent states in your DB: what if first save is successful and the second one isn’t? It’s even hard to imagine.

The solution is quite simple: use save! (with the exclamation at the end). This way if your validation fails your whole transaction will be rolled back (an exception will be raised by save! instead of returning false as the save does).