[RAILS] How to write migrationfile

index: It's there to duplicate a specific column in the table to speed up the search.

Create a user_id column with references: t.references: user and index user_id. (No foreign key constraints)

foreign_key: true: Paste a foreign key constraint. Prevents the id of a non-existent User from being registered in user_id. Prevents mistakes that erase records in the parent table.

add_foreign_key (: articles,: users) will add an index if there is no index, and reuse it if there is one. Therefore, the order of adding foreign key constraints → pasting indexes is not acceptable.

rails g model article body: text user: references


class CreateArticles < ActiveRecord::Migration[5.2]
  def change
    create_table :articles do |t|
      t.text :body
      t.references :user, foreign_key: true


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