Numeric colums for latitude / longitude in Rails 1.2 migrations

alewis (Andre Lewis) — Fri, 29 Dec 2006 14:36:23 GMT

In Rails 1.1.6, "numeric" datatypes didn't work in migrations. This confused a lot of people who wanted to store geographic data (latitude and longitude) for use in Google Maps and the like. Floats worked, but their precision is limited -- you'll lose three or more decimal places of precision if you store the results of a typical geocoding call in a Float column. And don't even think about using strings to store your latitudes/longitudes.

Fortunately, the numeric datatype problem is fixed in Rails 1.2, and you can now have do this in your migrations:



class CreatePlaces < ActiveRecord::Migration

  def self.up

    create_table :places do |t|

      t.column "lat", :decimal, :precision => 15, :scale => 10

      t.column "lng", :decimal, :precision => 15, :scale => 10

    end

  end



  def self.down

    drop_table :places

  end

end

FYI, if you're stuck on Rails 1.1.6, you can use this approach:



class CreatePlaces < ActiveRecord::Migration

  def self.up

    create_table :places do |t|

      t.column :lat, :float 

      t.column :lng, :float

    end

    execute("ALTER TABLE places MODIFY lat numeric(15,10);")

    execute("ALTER TABLE places MODIFY lng numeric(15,10);")

  end



  def self.down

    drop_table :places

  end

end

... but that's ugly, database-specific (works on MySQL), and not very DRY.

DZone Snippets: geo code

Numeric colums for latitude / longitude in Rails 1.2 migrations