ActiveRecord deprecation... so how are you supposed to write this, then?

active_record_deprecation_example.rb

gem 'activerecord', '= 6.0.4.6'
require 'active_record'
ActiveRecord::VERSION::STRING # => "6.0.4.6"

ActiveRecord::Base.establish_connection adapter: 'sqlite3', database: ':memory:'
ActiveRecord::Schema.define do
  self.verbose = false
  create_table(:users) { |t|
    t.string :user_name
    t.string :first_name
    t.string :last_name
  }
end

User = Class.new(ActiveRecord::Base) { has_many :posts }
User.create! user_name: 'Just Joshin', first_name: 'Josh', last_name: 'Cheek'
User.create!                           first_name: 'Jane', last_name: 'Doe'
User.create!                           first_name: 'Jenn'
User.create!                                               last_name: 'Smith'

User.pluck(:id, "coalesce(user_name, first_name||' '||last_name, first_name, last_name)")
# => [[1, "Just Joshin"], [2, "Jane Doe"], [3, "Jenn"], [4, "Smith"]]

# !> DEPRECATION WARNING: Dangerous query method (method whose arguments are used as raw SQL) called with non-attribute argument(s): "coalesce(user_name, first_name||' '||last_name, first_name, last_name)". Non-attribute arguments will be disallowed in Rails 6.1. This method should not be called with user-provided values, such as request parameters or model attributes. Known-safe values can be passed by wrapping them in Arel.sql(). (called from <main> at program.rb:21)