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Diffstat (limited to 'guides/source/association_basics.md')
| -rw-r--r-- | guides/source/association_basics.md | 132 |
1 files changed, 101 insertions, 31 deletions
diff --git a/guides/source/association_basics.md b/guides/source/association_basics.md index 61490ceb54..cd715aba1f 100644 --- a/guides/source/association_basics.md +++ b/guides/source/association_basics.md @@ -1,3 +1,5 @@ +**DO NOT READ THIS FILE ON GITHUB, GUIDES ARE PUBLISHED ON http://guides.rubyonrails.org.** + Active Record Associations ========================== @@ -101,13 +103,13 @@ class CreateOrders < ActiveRecord::Migration def change create_table :customers do |t| t.string :name - t.timestamps + t.timestamps null: false end create_table :orders do |t| t.belongs_to :customer, index: true t.datetime :order_date - t.timestamps + t.timestamps null: false end end end @@ -132,13 +134,13 @@ class CreateSuppliers < ActiveRecord::Migration def change create_table :suppliers do |t| t.string :name - t.timestamps + t.timestamps null: false end create_table :accounts do |t| t.belongs_to :supplier, index: true t.string :account_number - t.timestamps + t.timestamps null: false end end end @@ -165,13 +167,13 @@ class CreateCustomers < ActiveRecord::Migration def change create_table :customers do |t| t.string :name - t.timestamps + t.timestamps null: false end create_table :orders do |t| - t.belongs_to :customer, index:true + t.belongs_to :customer, index: true t.datetime :order_date - t.timestamps + t.timestamps null: false end end end @@ -207,19 +209,19 @@ class CreateAppointments < ActiveRecord::Migration def change create_table :physicians do |t| t.string :name - t.timestamps + t.timestamps null: false end create_table :patients do |t| t.string :name - t.timestamps + t.timestamps null: false end create_table :appointments do |t| t.belongs_to :physician, index: true t.belongs_to :patient, index: true t.datetime :appointment_date - t.timestamps + t.timestamps null: false end end end @@ -291,19 +293,19 @@ class CreateAccountHistories < ActiveRecord::Migration def change create_table :suppliers do |t| t.string :name - t.timestamps + t.timestamps null: false end create_table :accounts do |t| t.belongs_to :supplier, index: true t.string :account_number - t.timestamps + t.timestamps null: false end create_table :account_histories do |t| t.belongs_to :account, index: true t.integer :credit_rating - t.timestamps + t.timestamps null: false end end end @@ -332,12 +334,12 @@ class CreateAssembliesAndParts < ActiveRecord::Migration def change create_table :assemblies do |t| t.string :name - t.timestamps + t.timestamps null: false end create_table :parts do |t| t.string :part_number - t.timestamps + t.timestamps null: false end create_table :assemblies_parts, id: false do |t| @@ -371,13 +373,13 @@ class CreateSuppliers < ActiveRecord::Migration def change create_table :suppliers do |t| t.string :name - t.timestamps + t.timestamps null: false end create_table :accounts do |t| t.integer :supplier_id t.string :account_number - t.timestamps + t.timestamps null: false end add_index :accounts, :supplier_id @@ -455,7 +457,7 @@ class CreatePictures < ActiveRecord::Migration t.string :name t.integer :imageable_id t.string :imageable_type - t.timestamps + t.timestamps null: false end add_index :pictures, :imageable_id @@ -471,7 +473,7 @@ class CreatePictures < ActiveRecord::Migration create_table :pictures do |t| t.string :name t.references :imageable, polymorphic: true, index: true - t.timestamps + t.timestamps null: false end end end @@ -501,7 +503,7 @@ class CreateEmployees < ActiveRecord::Migration def change create_table :employees do |t| t.references :manager, index: true - t.timestamps + t.timestamps null: false end end end @@ -689,7 +691,7 @@ c.first_name = 'Manny' c.first_name == o.customer.first_name # => false ``` -This happens because c and o.customer are two different in-memory representations of the same data, and neither one is automatically refreshed from changes to the other. Active Record provides the `:inverse_of` option so that you can inform it of these relations: +This happens because `c` and `o.customer` are two different in-memory representations of the same data, and neither one is automatically refreshed from changes to the other. Active Record provides the `:inverse_of` option so that you can inform it of these relations: ```ruby class Customer < ActiveRecord::Base @@ -724,10 +726,10 @@ Most associations with standard names will be supported. However, associations that contain the following options will not have their inverses set automatically: -* :conditions -* :through -* :polymorphic -* :foreign_key +* `:conditions` +* `:through` +* `:polymorphic` +* `:foreign_key` Detailed Association Reference ------------------------------ @@ -879,10 +881,12 @@ class Order < ActiveRecord::Base belongs_to :customer, counter_cache: :count_of_orders end class Customer < ActiveRecord::Base - has_many :orders + has_many :orders, counter_cache: :count_of_orders end ``` +NOTE: You only need to specify the :counter_cache option on the "has_many side" of the association when using a custom name for the counter cache. + Counter cache columns are added to the containing model's list of read-only attributes through `attr_readonly`. ##### `:dependent` @@ -1495,6 +1499,7 @@ The `has_many` association supports these options: * `:as` * `:autosave` * `:class_name` +* `:counter_cache` * `:dependent` * `:foreign_key` * `:inverse_of` @@ -1522,6 +1527,10 @@ class Customer < ActiveRecord::Base end ``` +##### `:counter_cache` + +This option can be used to configure a custom named `:counter_cache`. You only need this option when you customized the name of your `:counter_cache` on the [belongs_to association](#options-for-belongs-to). + ##### `:dependent` Controls what happens to the associated objects when their owner is destroyed: @@ -1532,8 +1541,6 @@ Controls what happens to the associated objects when their owner is destroyed: * `:restrict_with_exception` causes an exception to be raised if there are any associated records * `:restrict_with_error` causes an error to be added to the owner if there are any associated objects -NOTE: This option is ignored when you use the `:through` option on the association. - ##### `:foreign_key` By convention, Rails assumes that the column used to hold the foreign key on the other model is the name of this model with the suffix `_id` added. The `:foreign_key` option lets you set the name of the foreign key directly: @@ -1979,8 +1986,8 @@ While Rails uses intelligent defaults that will work well in most situations, th ```ruby class Parts < ActiveRecord::Base - has_and_belongs_to_many :assemblies, autosave: true, - readonly: true + has_and_belongs_to_many :assemblies, -> { readonly }, + autosave: true end ``` @@ -1992,7 +1999,6 @@ The `has_and_belongs_to_many` association supports these options: * `:foreign_key` * `:join_table` * `:validate` -* `:readonly` ##### `:association_foreign_key` @@ -2236,3 +2242,67 @@ Extensions can refer to the internals of the association proxy using these three * `proxy_association.owner` returns the object that the association is a part of. * `proxy_association.reflection` returns the reflection object that describes the association. * `proxy_association.target` returns the associated object for `belongs_to` or `has_one`, or the collection of associated objects for `has_many` or `has_and_belongs_to_many`. + +Single Table Inheritance +------------------------ + +Sometimes, you may want to share fields and behavior between different models. +Let's say we have Car, Motorcycle and Bicycle models. We will want to share +the `color` and `price` fields and some methods for all of them, but having some +specific behavior for each, and separated controllers too. + +Rails makes this quite easy. First, let's generate the base Vehicle model: + +```bash +$ rails generate model vehicle type:string color:string price:decimal{10.2} +``` + +Did you note we are adding a "type" field? Since all models will be saved in a +single database table, Rails will save in this column the name of the model that +is being saved. In our example, this can be "Car", "Motorcycle" or "Bicycle." +STI won't work without a "type" field in the table. + +Next, we will generate the three models that inherit from Vehicle. For this, +we can use the `--parent=PARENT` option, which will generate a model that +inherits from the specified parent and without equivalent migration (since the +table already exists). + +For example, to generate the Car model: + +```bash +$ rails generate model car --parent=Vehicle +``` + +The generated model will look like this: + +```ruby +class Car < Vehicle +end +``` + +This means that all behavior added to Vehicle is available for Car too, as +associations, public methods, etc. + +Creating a car will save it in the `vehicles` table with "Car" as the `type` field: + +```ruby +Car.create color: 'Red', price: 10000 +``` + +will generate the following SQL: + +```sql +INSERT INTO "vehicles" ("type", "color", "price") VALUES ("Car", "Red", 10000) +``` + +Querying car records will just search for vehicles that are cars: + +```ruby +Car.all +``` + +will run a query like: + +```sql +SELECT "vehicles".* FROM "vehicles" WHERE "vehicles"."type" IN ('Car') +``` |