Rails Migration to convert string to integer using conversion

Question

There is a good question here I want to elaborate on. I am trying to convert a column in my database form a string to an integer.

I thought the conversion would be pretty straight forwrad. Currently my strings are

["10", "12", "125", "135", "140", ...]

My migration file includes:

def change
    change_column :table_name, :product_code, :integer
end

Rails tries this but Postgresql thows back an error.

PG::Error: ERROR: column "product_code" cannot be cast automatically to type integer
HINT: Specify a USING expression to perform the conversion.

I am not sure how I use this 'USING' expression in my rails migration.

So I thought the conversion would be pretty straight forward. What should I use as the USING expression?

Answer 1

change_column :table_name, :product_code,
  'integer USING CAST(product_code AS integer)'

Source: http://makandracards.com/makandra/18691-postgresql-vs-rails-migration-how-to-change-columns-from-string-to-integer