Add Single Table Inheritance (STI) to existing models - ruby

Question

I currently have multiple tables that are very similar. I should probably have created them with STI.
TypeOne < ActiveRecord::Base
TypeTwo < ActiveRecord::Base
TypeThree < ActiveRecord::Base
TypeOne(id: integer, parent_id: integer, created_at: datetime, updated_at: datetime)
TypeTwo(id: integer, parent_id: integer, created_at: datetime, updated_at: datetime)
TypeThree(id: integer, parent_id: integer, created_at: datetime, updated_at: datetime)
I am now trying to add STI to these. I created a BaseModel and added a type to that model.
BaseModel(id: integer, parent_id: integer, created_at: datetime, updated_at: datetime, type: string)
I also ran a migration and added to all of the types, a type column.
class AddTypeToTables < ActiveRecord::Migration
def change
add_column :type_ones, :type, :string
add_column :type_twos, :type, :string
add_column :type_threes, :type, :string
end
end
I want to combine all of the type tables into a STI. There is existing data in the models. If I were to combine them into a single table, I imagine the id's for the respective tables would conflict. For example:
#<TypeOne id: 4, parent_id: 1, created_at: "2015-05-08 18:39:09", updated_at: "2015-09-07 19:42:03">
#<TypeTwo id: 4, parent_id: 1, created_at: "2015-04-08 17:48:59", updated_at: "2015-09-07 14:17:48">
If I try to use becomes, it appears to change the class, but I cannot find the record in the BaseModel
TypeOne.last.becomes!(BaseModel)
#<BaseModel id: 4, parent_id: 1, created_at: "2015-05-08 18:39:09", updated_at: "2015-09-07 19:42:03">
BaseModel.all
=> []
I have also tried to change the type column of the inherited table to the basemodel
to = TypeOne.first
to.type = "BaseModel"
to.save
BaseModel.all
=> []
I have tried to change the classes for each to be a child of the BaseModel
TypeOne < BaseModel
TypeTwo < BaseModel
TypeThree < BaseModel
When I do this, I lose the connection to the existing data and each of the models appear empty.
How can I combine the existing tables?

Answer 1

As you've tagged it with PostgreSQL I'll include how to do what I suggested in my comment as an answer:
INSERT INTO base_model SELECT * FROM type_one ORDER BY id ASC;
INSERT INTO base_model SELECT * FROM type_two ORDER BY id ASC;
INSERT INTO base_model SELECT * FROM type_three ORDER BY id ASC;
To safely do this on a production dataset, put the SQL in a migration in db/migrate (i.e. in a file like db/migrate/20150907185938_integrate_tables.rb) and test it on your local database first. This should get you pretty close:
class IntegrateTables < ActiveRecord::Migration
def up
execute "INSERT INTO base_model SELECT * FROM type_one ORDER BY id ASC;"
execute "INSERT INTO base_model SELECT * FROM type_two ORDER BY id ASC;"
execute "INSERT INTO base_model SELECT * FROM type_three ORDER BY id ASC;"
end
def down
raise ActiveRecord::IrreversibleMigration, "It is unclear where original data stops and inserted data begins, can't migrate down"
end
end
Please mark this answer as accepted if it worked for you :)