The Lucid
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UX Designer, CSS Wizard, Ruby on Rails Developer.

Maintaining database column order with migrations

I like to keep database columns in a reasonably logical order. I generally keep primary keys as the first column, then content columns, then special usage columns, then foreign keys:

id
name
description
created_on
updated_on
account_id

Now, say I added a slug column with a migration:

def self.up
  add_column "projects", "slug", :string
end

That’s fine, I have my new column but it’s after my foreign keys:

id
name
description
created_on
updated_on
account_id
slug

What’s it doing down there? I want it after the name column! Wouldn’t it be nice if you could specify an :after option for add_column.
We can make this possible by monkey patching the add_column method at the top of our migration file:

module ActiveRecord
  module ConnectionAdapters # :nodoc:
    module SchemaStatements
      def add_column(table_name, column_name, type, options = {})
        add_column_sql = "ALTER TABLE #{table_name} ADD #{quote_column_name(column_name)} #{type_to_sql(type, options[:limit], options[:precision], options[:scale])}"
        after_column = options.delete(:after)
        add_column_options!(add_column_sql, options)
        add_column_sql << " AFTER #{after_column}" if after_column
        execute(add_column_sql)
      end
    end
  end
end

This lets us do the following:

def self.up
  add_column "projects", "slug", :string, :after => 'name'
end

Which gives us:

id
name
slug
description
created_on
updated_on
account_id

Much better. This may seem a little petty, however as your tables get more and more columns it makes things much easier to follow.

Please note: I have only tested this with MySQL.