Rails: How do I call `self.save` in my model and have it persist in the database?

Question

I'm trying to keep model logic within my model, but I can't get it to perform modifications on itself and have them persist in the database.

In my controller:

@article.perform_some_calulcations!

In my model:

def perform_some_calculations!
  self.foo.gsub!(/regexp/, 'string')
  self.save
end

If I drop debugger statements into my method and after my call to it in the controller, @article.foo has the correct value. However, when I continue, it doesn't persist in the database and webrick doesn't report any UPDATE statements.

What's going wrong? I don't know if I've ever had to do this before, but surely it's possible right?

Answer 1

Your problem was that if you modify an attribute "in place", this means: without assigning it a new value, then Rails will think that there is nothing new to be saved, so it "optimizes" the save away.

Each write accessor of your attribute will set a flag, so the save method will know that it should check whether the current value really differs from the value read from the database. That's why self.foo = self.foo.gsub(/regexp/, 'string') works (note that the exclamation mark is not necessary here).

If you need to modify an attribute "in place", for example with gsub! or replace, use:

def perform_some_calculations!
  foo_will_change!
  self.foo.gsub!(/regexp/, 'string')
  self.save
end