Help with primary_key_prefix_type

I put this config in environment.rb

  # Use table_id instead of id for primary key.   config.active_record.primary_key_prefix_type = :table_name_with_underscore

I have this migration:

class CreateEntities < ActiveRecord::Migration   def self.up     create_table :entities do |t|       t.string :entity_name, :null => false,                     :limit => 40       t.string :entity_legal_name, :null => false,                     :limit => 120       t.string :entity_legal_form, :null => false,                     :limit => 4

      t.timestamps     end

    add_index :entities, :entity_name,               :name => :idxU_entities_entity_name,               :unique => true   end

  def self.down     remove_index :entities, :name => :idxU_entities_entity_name     drop_table :entities   end end

When I run these rake tasks:

rake db:drop rake migrate

Then I see this:

# sqlite3 db/development.sqlite3 SQLite version 3.3.6 Enter ".help" for instructions

.schema entities

CREATE TABLE entities ("id" INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, "entity_name" varchar(40) NOT NULL, "entity_legal_name" varchar(120) NOT NULL, "entity_legal_form" varchar(4) NOT NULL, "created_at" datetime DEFAULT NULL, "updated_at" datetime DEFAULT NULL);

But I expected to see this:

CREATE TABLE entities ("entity_id" INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,...

It makes no difference if I pass the value to config.active_record.primary_key_prefix_type as a string or a symbol as neither works.

So, what am I doing wrong?