Ruby on Rails between :text text:?

Question

In Ruby on Rails, what is the difference between

:bonus_card

and

dependent: ?

(in the example

class TrainPassengers < ActiveRecord::Base
  has_one :bonus_card, dependent: :destroy
end

)

Answer 1

dependent: :destroy

is alternate syntax for:

:dependent => :destroy

It's new in Ruby 1.9.

:dependent, :destroy and :bonus_card are all symbols.

Answer 2

it is new syntax in ruby 1.9

   dependent: :destroy

which is alternative of this

  :dependent => :destroy

i think you are new in ruby because experienced person has idea about it and if you scaffold then dependent: :destroy this code is generated by rails by default now.

:dependent ,:destroy and :bonus_card are all symbols.Read about symbols these are very usefull

Answer 3

In Ruby, :something is a symbol. A symbol is a reference kept in memory and looked up quickly, so that it is a nice data type to use as hash keys. A Ruby Hash usually looks like:

{ :some_key => "some data", :other_key => 65536, :yet_another_key => :symbol_as_data }

Ruby 1.9 introduced a shorthand notation for writing the above, as long as keys are symbols, you can move the colon to the end and omit the fat arrow =>

{ some_key: "some data", other_key: 65536, yet_another_key: :symbol_as_data }

This is only valid for symbols passed as hash keys (also in hashes passed as method parameters). Other objects used as hash keys must still use the fat arrow(=>), and symbols used elsewhere are always written colon-first.