employee_nomethoderror.rb

require "sqlite3"
require "active_record"

ActiveRecord::Base.establish_connection(
  adapter: "sqlite3",
  database: ":memory:",
)

ActiveRecord::Schema.define do
  create_table "employees", force: :cascade do |t|
    t.string   "name"
    t.integer  "age"
    t.timestamps
  end
end

class Employee < ActiveRecord::Base
end

Employee.create!(name: "Caius", age: 0xBADC0FFEE)
Employee.create!(name: "Fred", age: 20)
Employee.create!(name: "George", age: 20)
Employee.create!(name: "Barty", age: 44)

Employee.where.not(name: %w[Fred George Barty])
# => [#<Employee:0x0000000133d205a8
#      id: 1,
#      name: "Caius",
#      age: 50159747054,
#      created_at: 2021-07-21 20:08:36 UTC,
#      updated_at: 2021-07-21 20:08:36 UTC>]

Employee.not.where(name: %w[Fred George Barty])
# ~> /Users/caius/.gem/ruby/2.6.5/gems/activerecord-6.1.4/lib/active_record/dynamic_matchers.rb:22:in `method_missing': undefined method `not' for #<Class:0x0000000133c53cd8> (NoMethodError)
# ~> Did you mean?  none
# ~> 	from -:28:in `<main>'