two database migration (active record)

rubyonrails-talk
1

Hello.

I want to write script, that will migrate one database (with models) to another database (with another models) using ActiveRecord and all of its benefits. It is possible? Please give me any tips.

I am moving database form old app to new one. It would be great to use ActiveRecord for this complex task.

Thank you.

rndrfero

2

I want to write script, that will migrate one database (with models) to another database (with another models) using ActiveRecord and all of its benefits. It is possible? Please give me any tips.

I am moving database form old app to new one. It would be great to use ActiveRecord for this complex task.

An important rule of programming is to always be as incremental as possible. The bigger a change you make, the higher the risks go.

If you want to deliver new features to a client, as soon as possible, leave the data in the old database, and hook up to them using ActiveRecord's system to set your models' table names, primary keys, etc.

The book /Rails Recipes/ lists these techniques under "Integrating with Legacy Database".

Don't make the mountain come to Mohammed, if Mohammed can just go to the mountain!

Over time, when you need new tables, or if you find occassion to refactor the existing tables, you can rename them closer to ActiveRecord's notorious opinions.

3

Steven Line wrote:

Hi Frantisek,

I recently did this. Here is some code, maybe you can figure it out from this. If not post questions.

  # copying data from table named legacy_aid_stations to table   # named aid_stations   def migrate_aid_stations     # connect to legacy table. :legacy_development is defined in     # databases.yml     LegacyAidStation.establish_connection(:legacy_development)

    # get all rows from legacy table     @lAidStations = LegacyAidStation.find(:all)

    # clear any rows that may be in new table     AidStation.delete_all     @aidStations = Array.new     @lAidStations.each do |l|       aidStation = AidStation.new

      # copy fields from legacy object to new object       aidStation.name = l.AidStationName.split(/ /).map {|word|           word.capitalize}.join ' ' # capitalize 1st letter of each word       aidStation.sortOrderCW = l.SortOrderCW       aidStation.sortOrderCCW = l.SortOrderCCW

      aidStation.save       @aidStations.push aidStation     end   end

Here's the definition of :legacy_development in databases.yml:

legacy_development:   adapter: mysql   database: hardrockOrig   username: root   password: booyah   socket: /tmp/mysql.sock