There are many approaches out there how you can import data from a legacy application to a new application. Here is an approach which opens two database connections and uses active record for the legacy system, too:
1. Add you database information to you config/database.yml.
data_migration:
database: your_application_data_migration
2. Create a separate application record for the data migration, e.g. in app/data_migration/migration_record.rb. You will need to create an app/data_migration.rb class first.
class DataMigration::MigrationRecord < ActiveRecord::Base
self.abstract_class = true
establish_connection(:data_migration)
end
3. Inherit from this class in the migration models, e.g. app/data_migration/user.rb.
class DataMigration::MigrationUser < DataMigration::MigrationRecord
self.table_name = 'zz_1234_0' # you will need this if the table name is not data_migration_migration_users
self.primary_key = 'data_id' # you will need this if the primary key is not id
alias_attribute :title, :c1254
alias_attribute :first_name, :c1255
alias_attribute :last_name, :c1256
alias_attribute :email, :c1257
alias_attribute :phone, :c1258
end
4. Extend your app/models/data_migration.rb
class DataMigration
def run
migrate_users
end
def migrate_users
DataMigration::MigrationUser.find_each do |migration_user|
User.create!(
title: migration_user.title,
first_name: migration_user.first_name,
last_name: migration_user.last_name,
email: migration_user.email,
phone: migration_user.phone
)
end
end
end
Now the best idea is to test this in the rails sandbox (so your development data stay untouched):
rails console --sandbox
2.4.1 :003 > DataMigration.new.run
Keep in mind our best practices for data migrations.
Posted by Emanuel to makandra dev (2017-08-14 11:19)