When I run the rake:db migrate command I get an error "Uninitialized constant CreateArticles"

Solution 1:

Be sure that your file name and class name say the same thing(except the class name is camel cased).The contents of your migration file should look something like this, simplified them a bit too:

#20090106022023_create_articles.rb
class CreateArticles < ActiveRecord::Migration   
  def self.up
    create_table :articles do |t|
      t.belongs_to :user, :category
      t.string :title
      t.text :synopsis, :limit => 1000
      t.text :body, :limit => 20000
      t.boolean :published, :default => false
      t.datetime :published_at
      t.timestamps
    end
  end

  def self.down
    drop_table :articles
  end
end

Solution 2:

It's possible to get the given error if your class names don't match inflections (like acronyms) from config/initializers/inflections.rb.

For example, if your inflections include:

ActiveSupport::Inflector.inflections(:en) do |inflect|
  inflect.acronym 'DOG'
end

then you might need to make sure the class in your migration is:

class CreateDOGHouses < ActiveRecord::Migration[5.0]

rather than:

class CreateDogHouses < ActiveRecord::Migration[5.0]

Not super common, but if you generate a migration or a model or something, and then add part of it to inflections afterwards it may happen. (The example here will cause NameError: uninitialized constant CreateDOGHouses if your class name is CreateDogHouses, at least with Rails 5.)