Rails: Adding an index after adding column

Question

Suppose I created a table table in a Rails app. Some time later, I add a column running:

rails generate migration AddUser_idColumnToTable user_i         


        

Answer 1

For those who are using postgresql db and facing error

StandardError: An error has occurred, this and all later migrations canceled:

=== Dangerous operation detected #strong_migrations ===

Adding an index non-concurrently blocks writes

please refer this article

example:

class AddAncestryToWasteCodes < ActiveRecord::Migration[6.0]
  disable_ddl_transaction!

  def change
    add_column :waste_codes, :ancestry, :string
    add_index :waste_codes, :ancestry, algorithm: :concurrently
  end
end