Question

I am new to ruby on rails, could anybody explain what does the symbol ‘:’ mean, what would be ‘validates’ and ‘create_table’? So much confused…

class Post < ActiveRecord::Base
   validates :name, :presence => true
   validates :title, :presence => true, :length => {:minimum => 5}
end

class CreatePosts < ActiveRecord::Migration
   def change
     create_table :posts do |t|
       t.string :name
       t.string :title
       t.text :content
       t.timestamps
     end
    end
 end

Answer 1

1. The colon character (:) is the beginning of a syntax literal for a Ruby “Symbol”:

   :abc.class # => Symbol
   "abc".to_sym # => :abc

   Symbols are like strings but they are “interned”, meaning the Ruby interpreter only has a single copy of it in memory despite multiple possible references (whereas there can be many equivalent strings in memory at once).

2. The ‘validates‘ token in your example above is a class method (of something in the class hierarchy of the “Post class”) that is being called with a symbol argument (:name) and a hash argument with a single key/value pair of :presence => true.

3. The ‘create_table‘ token is a method which is being called with a single argument (the symbol “:posts“) and is given a block which takes a single argument “t” (do |t| ... end).