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Diffstat (limited to 'guides/source/association_basics.md')
| -rw-r--r-- | guides/source/association_basics.md | 30 |
1 files changed, 23 insertions, 7 deletions
diff --git a/guides/source/association_basics.md b/guides/source/association_basics.md index 6e68935f9b..bead931529 100644 --- a/guides/source/association_basics.md +++ b/guides/source/association_basics.md @@ -154,7 +154,7 @@ case, the column definition might look like this: ```ruby create_table :accounts do |t| - t.belongs_to :supplier, index: true, unique: true, foreign_key: true + t.belongs_to :supplier, index: { unique: true }, foreign_key: true # ... end ``` @@ -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. @@ -944,7 +960,7 @@ class Author < ApplicationRecord end ``` -NOTE: You only need to specify the :counter_cache option on the `belongs_to` +NOTE: You only need to specify the `:counter_cache` option on the `belongs_to` side of the association. Counter cache columns are added to the containing model's list of read-only attributes through `attr_readonly`. @@ -1401,7 +1417,7 @@ If either of these saves fails due to validation errors, then the assignment sta If the parent object (the one declaring the `has_one` association) is unsaved (that is, `new_record?` returns `true`) then the child objects are not saved. They will automatically when the parent object is saved. -If you want to assign an object to a `has_one` association without saving the object, use the `association.build` method. +If you want to assign an object to a `has_one` association without saving the object, use the `build_association` method. ### `has_many` Association Reference @@ -1543,7 +1559,7 @@ The `collection.size` method returns the number of objects in the collection. The `collection.find` method finds objects within the collection. It uses the same syntax and options as `ActiveRecord::Base.find`. ```ruby -@available_books = @author.books.find(1) +@available_book = @author.books.find(1) ``` ##### `collection.where(...)` @@ -1815,7 +1831,7 @@ The `limit` method lets you restrict the total number of objects that will be fe class Author < ApplicationRecord has_many :recent_books, -> { order('published_at desc').limit(100) }, - class_name: "Book", + class_name: "Book" end ``` |