How to format values before saving to database in rails 3

First of all, this:

def format_values
  self.profit.to_s.delete!('^0-9') unless self.profit.nil?
end

is pretty much the same as this:

def format_values
    return if(self.profit.nil?)
    p = self.profit
    s = p.to_s
    s.delete!('^0-9')
end

So there's no reason to expect your format_values method to have any effect whatsoever on self.profit.

You could of course change format_values to assign the processed string to self.profit but that won't help because your cleansing logic is in the wrong place and it will be executed after '$1,000' has been turned into a zero.

When you assign a value to a property, ActiveRecord will apply some type conversions along the way. What happens when you try to convert '$1,000' to a number? You get zero of course. You can watch this happening if you play around in the console:

> a = M.find(id)
> puts a.some_number
11
> a.some_number = 'pancakes'
 => "pancakes"
> puts a.some_number
0
> a.some_number = '$1,000'
 => "1,000"
> puts a.some_number
0
> a.some_number = '1000'
 => "1000"
> puts a.some_number
1000

So, your data cleanup has to take place before the data goes into the model instance because as soon as AR gets its hands on the value, your '$1,000' will become 0 and all is lost. I'd put the logic in the controller, the controller's job is to mediate between the outside world and the models and data formatting and mangling certainly counts as mediation. So you could have something like this in your controller:

def some_controller
    fix_numbers_in(:profit)
    # assign from params as usual...
end

private

def fix_numbers_in(*which)
    which.select { |p| params.has_key?(p) }.each do |p|
        params[p] = params[p].gsub(/\D/, '') # Or whatever works for you
    end
end

Then everything would be clean before ActiveRecord gets its grubby little hands on your data and makes a mess of things.

You could do similar things by overriding the profit= method in your model but that's really not the model's job.

class User < ActiveRecord::Base
  before_save :format_values

  private

  def format_values
    self.profit = profit.to_s.gsub(/\D/,'') if profit
  end
end

  def format_values
    self.profit.to_d!
  end

I recommend you to write custom setter for this particular instance variable @profit:

class User
  attr_accessor :profit

  def profit= value    
    @profit = value.gsub(/\D/,'')
  end
end

u = User.new
u.profit = "$1,000"
p u.profit # => "1000"

I would suggest using the rails helper of number with precision. Below is some code.

Generic Example:

number_with_precision(111.2345, :precision => 1, :significant => true)     # => 100

Rails code Example:

def profit=(new_profit)
  number_with_precision(self[:profit], :precision => 1, :significant => true)
end