[いつか記事にするよう][自分用メモ]マイグレーションファイルについて　

rake db:migrate:status

$ rails g migration change_column_default_to_users

class ChangeColumnDefaultToUsers < ActiveRecord::Migration[5.2]
  def change
    change_column_default :users, :name, from: nil, to: ""
  end
end

rails db:migrate

rails g migration change_colum_null_name_users

class ChangeColumDefaultNullUsers < ActiveRecord::Migration[6.1]
  def change
    change_column_null :users, :name, false, 0
  end
end

rails db:migrate

rails g migration モデル名　カラム名:データ型

class ChangeColumnDefaultToUsers < ActiveRecord::Migration[5.2]
  def change
    add_column_ :users, :モデル名, カラム名, : データ型
  end
end

rails db:migrate

rails g migration ChangeDatetipeReferencetoposts

change_column :posts, :researcher_id, :references, foreign_key: true

rails db:migrate

rails g migration  AddResearcherIdToPosts

def change
    execute 'DELETE FROM Posts;'
    add_reference :posts, :researcher, null: false, index: true
end