Database Migration Error

[Jeremy Canning]

I am attempting to integrate this ratyrate gem into my rails application. After installing the gem running rails g ratyrate [my user equivalent] when I subsequently attempt to migrate the database, I continually get the following error:

$ rails db:migrate
== 20190508052745 CreateRates: migrating ======================================
-- create_table(:rates)
   -> 0.0033s
-- add_index(:rates, :rater_id)
rails aborted!
StandardError: An error has occurred, this and all later migrations canceled:

Index name 'index_rates_on_rater_id' on table 'rates' already exists
...

The only way I've found to bypass this problem is to comment out or remove the add_index lines from the create_rates and create_rating_caches migrations, but I'm not sure if I would lose the functionality of the gem. Regardless I'm getting this issue from a fresh install.

[Andre Mellentin]

just change it to the following and this will work:

class CreateRates < ActiveRecord::Migration[5.1]
  def self.change
    create_table :rates do |t|
      t.belongs_to :rater
      t.belongs_to :rateable, polymorphic: true
      t.float :stars, null: false
      t.string :dimension
      t.timestamps
    end
    add_index :rates, [:rateable_id, :rateable_type]
  end
end