Ruby on rails migration error - ruby-on-rails

Question

I installed a gem acts-as-taggable-on whenever i tried to run rails db:migrate it would output this:
C:\Sites\novosti>rails db:migrate
rails aborted!
StandardError: An error has occurred, this and all later migrations canceled:
Directly inheriting from ActiveRecord::Migration is not supported. Please specify the Rails release the migration was written for:
class ActsAsTaggableOnMigration < ActiveRecord::Migration[4.2]
C:/Sites/novosti/db/migrate/20170708123900_acts_as_taggable_on_migration.acts_as_taggable_on_engine.rb:2:in `<top (required)>'
bin/rails:4:in `require'
bin/rails:4:in `<main>'
StandardError: Directly inheriting from ActiveRecord::Migration is not supported. Please specify the Rails release the migration was written for:
class ActsAsTaggableOnMigration < ActiveRecord::Migration[4.2]
C:/Sites/novosti/db/migrate/20170708123900_acts_as_taggable_on_migration.acts_as_taggable_on_engine.rb:2:in `<top (required)>'
bin/rails:4:in `require'
bin/rails:4:in `<main>'
Tasks: TOP => db:migrate
(See full trace by running task with --trace)
So i just added [5.1] and it fixed the problem but another one appeared
C:\Sites\novosti>rails db:migrate
== 20170708123900 ActsAsTaggableOnMigration: migrating ========================
-- create_table(:tags)
-> 0.0028s
-- create_table(:taggings)
-> 0.0033s
-- add_index(:taggings, :tag_id)
rails aborted!
StandardError: An error has occurred, this and all later migrations canceled:
Index name 'index_taggings_on_tag_id' on table 'taggings' already exists
C:/Sites/novosti/db/migrate/20170708123900_acts_as_taggable_on_migration.acts_as_taggable_on_engine.rb:23:in `up'
bin/rails:4:in `require'
bin/rails:4:in `<main>'
ArgumentError: Index name 'index_taggings_on_tag_id' on table 'taggings' already exists
C:/Sites/novosti/db/migrate/20170708123900_acts_as_taggable_on_migration.acts_as_taggable_on_engine.rb:23:in `up'
bin/rails:4:in `require'
bin/rails:4:in `<main>'
Tasks: TOP => db:migrate
(See full trace by running task with --trace)

Answer 1

Index name on a table should be unique. So this is an error from db as the the index already exists. Please drop the index on the table of the db before migration or you can remove the add_index in migration if the index is already ok in the table