Adding a custom column data type in Active Record

On my local machine I develop my Rails application using MySQL, but on deployment I am using Heroku which uses PostgreSQL. I am in need of creating a new data type, specifically I wish to call it longtext, and it is going to need to map to separate column types in either database.

I have been searching for this. My basic idea is that I am going to need to override some hash inside of the ActiveRecord::ConnectionAdapters::*SQL adapter(s) but I figured I would consult the wealth of knowledge here to see if this is a good approach (and, if possible, pointers on how to do it) or if there is a quick win another way.

Right now the data type is "string" and I am getting failed inserts because the data type is too long. I want the same func开发者_运维知识库tionality on both MySQL and PgSQL, but it looks like there is no common data type that gives me an unlimited text blob column type?

The idea is that I want to have this application working correctly (with migrations) for both database technologies.

Much appreciated.

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Why don't you install PostgreSQL on your dev machine? Download it, click "ok" a few times and you're up and running. It isn't rocket science :-)

http://www.postgresql.org/download/

PostgreSQL doesn't have limitations on datatypes, you can create anything you want, it's up to your imagination:

CREATE DOMAIN (simple stuff only)

CREATE TYPE (unlimited)

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The SQL that Frank mentioned is actually the answer, but I really was looking for a more specific way to do RDBMS specific Rails migrations. The reason is that I want to maintain the fact that my application can run on both PostgreSQL and MySQL.

class AddLongtextToPostgresql < ActiveRecord::Migration
  def self.up
    case ActiveRecord::Base.connection.adapter_name
    when 'PostgreSQL'
      execute "CREATE DOMAIN longtext as text"
      execute "ALTER TABLE chapters ALTER COLUMN html TYPE longtext"
      execute "ALTER TABLE chapters ALTER COLUMN body TYPE longtext"
    else
      puts "This migration is not supported on this platform."
    end
  end

  def self.down
  end
end

That is effectively what I was looking for.