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Ruby on Rails 5.1.5 - Migration Error (Relation already exists) in following TutorialsPoint tutorial

I am following this Ruby on Rails tutorial from TutorialsPoint.com. I'm completely new to Ruby on Rails development, and already running into some hiccups.

I am using Ruby 2.3.3p222 (2016-11-21 revision 56859) [i386-mingw32] and Ruby on Rails 5.1.5.

For some reason, after adding list.html.erb with the code specified and trying to run "rails server", upon opening up http://localhost:3000, I get this migration error:

PendingMigrationError

When I run "rails db:migrate RAILS_ENV=development", I get this log of errors in the console:

C:\Users\gregp\Documents\<secret directory>\Programming Experiments\TutorialsPointRoR\demo2>rails db:migrate RAILS_ENV=development
== 20180221025323 Books: migrating ============================================
-- create_table(:books)
rails aborted!
StandardError: An error has occurred, this and all later migrations canceled:

PG::DuplicateTable: ERROR:  relation "books" already exists
: CREATE TABLE "books" ("id" bigserial primary key, "title" character varying(32) NOT NULL, "price" float, "subject_id" integer, "description" text, "created_at" timestamp)
C:/Users/gregp/Documents/<secret directory>/Programming Experiments/TutorialsPointRoR/demo2/db/migrate/20180221025323_books.rb:3:in `up'
bin/rails:4:in `require'
bin/rails:4:in `<main>'

Caused by:
ActiveRecord::StatementInvalid: PG::DuplicateTable: ERROR:  relation "books" already exists
: CREATE TABLE "books" ("id" bigserial primary key, "title" character varying(32) NOT NULL, "price" float, "subject_id" integer, "description" text, "created_at" timestamp)
C:/Users/gregp/Documents/<secret directory>/Programming Experiments/TutorialsPointRoR/demo2/db/migrate/20180221025323_books.rb:3:in `up'
bin/rails:4:in `require'
bin/rails:4:in `<main>'

Caused by:
PG::DuplicateTable: ERROR:  relation "books" already exists
C:/Users/gregp/Documents/<secret directory>/Programming Experiments/TutorialsPointRoR/demo2/db/migrate/20180221025323_books.rb:3:in `up'
bin/rails:4:in `require'
bin/rails:4:in `<main>'
Tasks: TOP => db:migrate
(See full trace by running task with --trace)

I have these files in the db/migrate directory (I don't know why even when I started creating the project, it created a pair of migrate files for the Books table and another for the Subjects table):

20180221024754_create_books.rb:

class CreateBooks < ActiveRecord::Migration[5.1]
  def change
    create_table :books do |t|
       t.column :title, :string, :limit => 32, :null => false
       t.column :price, :float
       t.column :subject_id, :integer
       t.column :description, :text
       t.column :created_at, :timestamp
    end
  end
end

20180221024922_create_subjects.rb:

class CreateSubjects < ActiveRecord::Migration[5.1]
  def change
    create_table :subjects do |t|
       t.column :name, :string
    end

    Subject.create :name => "Physics"
    Subject.create :name => "Mathematics"
    Subject.create :name => "Chemistry"
    Subject.create :name => "Psychology"
    Subject.create :name => "Geography"
  end
end

20180221025323_books.rb:

class Books < ActiveRecord::Migration[5.1]
  def self.up
      create_table :books do |t|
         t.column :title, :string, :limit => 32, :null => false
         t.column :price, :float
         t.column :subject_id, :integer
         t.column :description, :text
         t.column :created_at, :timestamp
      end
   end

   def self.down
      drop_table :books
  end
end

20180221025434_subjects.rb:

class Subjects < ActiveRecord::Migration[5.1]
  def self.up

     create_table :subjects do |t|
        t.column :name, :string
     end

     Subject.create :name => "Physics"
     Subject.create :name => "Mathematics"
     Subject.create :name => "Chemistry"
     Subject.create :name => "Psychology"
     Subject.create :name => "Geography"
  end

  def self.down
     drop_table :subjects
  end
end

This is really strange, because I don't think I am supposed to have duplicate code between the migrate files. I don't even see the significance of using the self.up and self.down functions when I'm only creating the database for now and using it for the tutorial as a whole.

What should I do to fix this problem? I think I need to get rid of the self.up and self.down functions, and run rake db:migrate again, but I don't know if there's an extra step needed or another way.

Solution

  • I'm not sure where the tutorial is from, but those last two migration files look like they might be there from a previous version.

    Try deleting them and restart the Rails server and see if that fixes it.

    If not reset the database by running rails db:reset (that's the equivalent of dropping the database and then recreating it. Any data in the database will be lost, but I don't think that should be an issue for you).