How to create a migration file dynamically from a rake task or a lib file in rails 4.0

If you want to add a migration file from lib file or somewhere from your ruby file and execute it, use the dynamic method which can create a class or method dynamically. The following code snippet is not complete. But gives a better idea to create migration file dynamically. Use a bit of metaprogramming.

 def create_columns(tb_with_cols)
    .........
    .........
    columns.each { |column| add_columns << "\tadd_column(':#{tb_name}', :#{column})\n" }
    columns
 end

 def migration_file_content(tb_with_cols)
<<-RUBY
  class AddMissingColumnsToTable < ActiveRecord::Migration
     def change_table
    #{create_columns(tb_with_cols)}
   end
 end
  RUBY
 end


 def write_content_to_file(path, content)
    File.open(path, 'w+') do |f|
      f.write(content)
    end
 end

Just call the method ‘migration_file_content’ in your code. Pass the parameter tb_with_cols as a Hash whose key is the table_name and value is the columns that should be added to that table like:

tb_with_cols = {:users => {:name => :string, :age => :integer, :address => :text} }

After that just call the method ‘write_content_to_file’ with your new migration file path and the content from our ‘migration_file_content’ method. 🙂

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Author: Abhi

Hi, this is Abhilash - Senior Programmer Analyst at CoMakeIT, specialised on web programming. Mainly working on Ruby On Rails platform since 2010.

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