Rails increase db value by one

Question

Hi,

I have a Pages table in my DB with a field called position.

How can I increase that value by one before it's saved?

Even better how can I remove unused positions and give the new record the correct position number?

Answer 1

You need a before_save callback:

In your Page model:

before_save :increase_position

def increase_position
  self.position += 1
end

You can add any kind of logic to the increase_position method to remove unused positions.

Answer 2

you need to use the acs_as_list plugin or setup some before and after filters.

before_create :set_position
after_destroy :fix_positions

def set_position
   self.position = Page.count + 1
end

def fix_positions
  Page.order('position asc').all.each_with_index do |page, index|
    page.update_attribute(:position, index + 1) unless page.position == index + 1
  end
end