Ruby on Rails

C:\rubytest\proj>rails new abc1

..................

C:\rubytest\proj>cd abc1

C:\rubytest\proj\abc1>cd app\models

C:\rubytest\proj\abc1\app\models>notepad blah.rb

C:\rubytest\proj\abc1\app\models>type blah.rb

class Blah < ApplicationRecord

end

C:\rubytest\proj\abc1\app\models>rails console

Loading development environment (Rails 5.1.5)

irb(main):001:0> Blah.new

ActiveRecord::StatementInvalid: Could not find table 'blahs'

        from (irb):1

^^ No surprises there.

irb(main):002:0> am=ActiveRecord::Migration

=> ActiveRecord::Migration

irb(main):003:0> am.create_table(:blahs)

-- create_table(:blahs)

   (0.0ms)  SELECT sqlite_version(*)

   (6.0ms)  CREATE TABLE "blahs" ("id" INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL)

   -> 0.0098s

=> []

irb(main):004:0> Blah.new

=> #<Blah id: nil>

^^^ There we see that the rails console has re-read the database in some sense  since it is now aware that we have a :blahs table.

irb(main):005:0> am.drop_table :blahs

-- drop_table(:blahs)

   (7.0ms)  DROP TABLE "blahs"

   -> 0.0087s

=> []

irb(main):009:0> am.connection.tables

=> []

irb(main):010:0> Blah.new

=> #<Blah id: nil>

^^^ So we see that  drop_table  doesn't lead to any kind of a refresh of the rails console.  

  The rails console is in some ways oblivious to the fact that the table has been dropped.    am.connection.tables works fine..  it picks up that the table has been dropped.  But given that I can still do Blah.new  it shows the rails console hasn't done any kind of full refresh..  I know that if I was to exit the rails console and go back in, or do reload!, then it'd pick up that the table is dropped and Blah.new will then give an error as it shoudl.

irb(main):011:0> reload!

Reloading...

=> true

irb(main):012:0> Blah.new

ActiveRecord::StatementInvalid: Could not find table 'blahs'

        from (irb):12

irb(main):013:0> am.create_table(:blahs)

-- create_table(:blahs)

   (0.0ms)  SELECT sqlite_version(*)

   (3.0ms)  CREATE TABLE "blahs" ("id" INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL)

   -> 0.0048s

=> []

irb(main):014:0> Blah.new

=> #<Blah id: nil>

irb(main):015:0> am.drop_table :blahs

-- drop_table(:blahs)

   (5.0ms)  DROP TABLE "blahs"

   -> 0.0063s

=> []

irb(main):016:0> am.create_table(:blahs) {|t| t.string :gg}

-- create_table(:blahs)

   (4.0ms)  CREATE TABLE "blahs" ("id" INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, "gg" varchar)

   -> 0.0059s

=> []

irb(main):017:0> Blah.new

=> #<Blah id: nil>

Here after dropping the table.. knowing that rails console doesn't pick that up in a way that will affect Blah.new  

I then do  create_table  to see if it picks that up.. And the strange thing is it doesn't really.      The create table line I did made a new column.

Rails Console is still picking up the earlier create_table.

irb(main):018:0> reload!

Reloading...

=> true

irb(main):019:0> Blah.new

=> #<Blah id: nil, gg: nil>

irb(main):020:0>