gem "ar-sequence"

class CreateUsers < ActiveRecord::Migration[5.2]
 def up
   create_sequence :position
 end

 def down
   drop_sequence :position
 end
end

create_sequence :position, increment: 2
create_sequence :position, start: 100

class CreateThings < ActiveRecord::Migration[5.2]
  def change
    create_sequence :position

    create_table :things do |t|
      t.text :name

      # PostgreSQL uses bigint as the sequence's default type.
      # Use a block to specify the default value on migrations.
      t.bigint :position,
                null: false,
                default: -> { "nextval('position')" }

      t.timestamps
    end
  end
end

# Advance sequence and return new value
ActiveRecord::Base.nextval("position")

# Return value most recently obtained with nextval for specified sequence.
ActiveRecord::Base.currval("position")

# Set sequence's current value
ActiveRecord::Base.setval("position", 1234)