primary key memo

Again, make a note to make sure you understand So that it can be verbalized

What is a primary key

DB key Identify the ** data (rows, records) ** of the DB ** uniquely (no other data is the same) ** Items for

[For some reason] Speaking of "data whose primary key value is XX" Because you can immediately judge "Oh, this data (row, record)"

Also called "** primary key **"

role

・ Table ** Search speed ** is significantly ** faster ** -Guarantee ** integrity ** of table data

Rails ・ Specifications that id is added by default -You may want to set a character string or something as a ** primary key . → You can ** cancel the setting to automatically set the primary key as an ID with " id: false " ** → Set " primary_key: true **" for the column you want to set as the primary key.

migration file

class Hoge < ActiveRecord::Migration[5.2]
  def change
    # id:Add false
    create_table :hogehoge, id: false do |t| 
      # primary_key:Add true
      t.integer :user_id, null: false, primary_key: true
      t.string :name

Note ・ ** Composite keys (composite_primary_keys) ** ・ ** Gem ** called composite_primary_keys

Reference article

https://wa3.i-3-i.info/word1991.html https://www.sejuku.net/blog/52356 http://www.code-magagine.com/?p=12207 https://qiita.com/tanutanu/items/6c53b5290eaa9bf905d3 https://qiita.com/belion_freee/items/8f8f1d1e5333da561fd8