From e1567d0d3a3c0ae1f4da1fb8b5b77a85767fb6ae Mon Sep 17 00:00:00 2001 From: Krzysztof Maicher Date: Sat, 4 Mar 2017 17:26:23 +0100 Subject: Improve foreign key description in guides [ci skip] --- guides/source/association_basics.md | 20 ++++++++++++++++++-- 1 file changed, 18 insertions(+), 2 deletions(-) (limited to 'guides/source/association_basics.md') diff --git a/guides/source/association_basics.md b/guides/source/association_basics.md index 73c9c10c1f..5794bfa666 100644 --- a/guides/source/association_basics.md +++ b/guides/source/association_basics.md @@ -582,14 +582,30 @@ class CreateBooks < ActiveRecord::Migration[5.0] t.string :book_number t.integer :author_id end - - add_index :books, :author_id end end ``` If you create an association some time after you build the underlying model, you need to remember to create an `add_column` migration to provide the necessary foreign key. +It's a good practice to add an index on the foreign key to improve queries +performance and a foreign key constraint to ensure referential data integrity: + +```ruby +class CreateBooks < ActiveRecord::Migration[5.0] + def change + create_table :books do |t| + t.datetime :published_at + t.string :book_number + t.integer :author_id + end + + add_index :books, :author_id + add_foreign_key :books, :authors + end +end +``` + #### Creating Join Tables for `has_and_belongs_to_many` Associations If you create a `has_and_belongs_to_many` association, you need to explicitly create the joining table. Unless the name of the join table is explicitly specified by using the `:join_table` option, Active Record creates the name by using the lexical book of the class names. So a join between author and book models will give the default join table name of "authors_books" because "a" outranks "b" in lexical ordering. -- cgit v1.2.3