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Diffstat (limited to 'guides/source/association_basics.md')
| -rw-r--r-- | guides/source/association_basics.md | 89 |
1 files changed, 37 insertions, 52 deletions
diff --git a/guides/source/association_basics.md b/guides/source/association_basics.md index b5bd24d027..e7408b5a7f 100644 --- a/guides/source/association_basics.md +++ b/guides/source/association_basics.md @@ -94,7 +94,7 @@ class Book < ApplicationRecord end ``` - + NOTE: `belongs_to` associations _must_ use the singular term. If you used the pluralized form in the above example for the `author` association in the `Book` model, you would be told that there was an "uninitialized constant Book::Authors". This is because Rails automatically infers the class name from the association name. If the association name is wrongly pluralized, then the inferred class will be wrongly pluralized too. @@ -127,7 +127,7 @@ class Supplier < ApplicationRecord end ``` - + The corresponding migration might look like this: @@ -171,7 +171,7 @@ end NOTE: The name of the other model is pluralized when declaring a `has_many` association. - + The corresponding migration might look like this: @@ -213,7 +213,7 @@ class Patient < ApplicationRecord end ``` - + The corresponding migration might look like this: @@ -299,7 +299,7 @@ class AccountHistory < ApplicationRecord end ``` - + The corresponding migration might look like this: @@ -340,7 +340,7 @@ class Part < ApplicationRecord end ``` - + The corresponding migration might look like this: @@ -439,7 +439,7 @@ end The simplest rule of thumb is that you should set up a `has_many :through` relationship if you need to work with the relationship model as an independent entity. If you don't need to do anything with the relationship model, it may be simpler to set up a `has_and_belongs_to_many` relationship (though you'll need to remember to create the joining table in the database). -You should use `has_many :through` if you need validations, callbacks or extra attributes on the join model. +You should use `has_many :through` if you need validations, callbacks, or extra attributes on the join model. ### Polymorphic Associations @@ -494,7 +494,7 @@ class CreatePictures < ActiveRecord::Migration[5.0] end ``` - + ### Self Joins @@ -505,7 +505,7 @@ class Employee < ApplicationRecord has_many :subordinates, class_name: "Employee", foreign_key: "manager_id" - belongs_to :manager, class_name: "Employee" + belongs_to :manager, class_name: "Employee", optional: true end ``` @@ -572,40 +572,32 @@ class Book < ApplicationRecord end ``` -This declaration needs to be backed up by the proper foreign key declaration on the books table: +This declaration needs to be backed up by a corresponding foreign key column in the books table. For a brand new table, the migration might look something like this: ```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 + t.datetime :published_at + t.string :book_number + t.references :author end 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: +Whereas for an existing table, it might look like this: ```ruby -class CreateBooks < ActiveRecord::Migration[5.0] +class AddAuthorToBooks < 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 + add_reference :books, :author end end ``` +NOTE: If you wish to [enforce referential integrity at the database level](/active_record_migrations.html#foreign-keys), add the `foreign_key: true` option to the ‘reference’ column declarations above. + #### 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. @@ -735,12 +727,9 @@ a.first_name = 'David' a.first_name == b.author.first_name # => true ``` -Active Record supports automatic identification for most associations with standard names. However, Active Record will not automatically identify bi-directional associations that contain any of the following options: +Active Record supports automatic identification for most associations with standard names. However, Active Record will not automatically identify bi-directional associations that contain a scope or any of the following options: -* `:conditions` * `:through` -* `:polymorphic` -* `:class_name` * `:foreign_key` For example, consider the following model declarations: @@ -787,12 +776,6 @@ a.first_name = 'David' a.first_name == b.writer.first_name # => true ``` -There are a few limitations to `:inverse_of` support: - -* They do not work with `:through` associations. -* They do not work with `:polymorphic` associations. -* They do not work with `:as` associations. - Detailed Association Reference ------------------------------ @@ -804,7 +787,7 @@ The `belongs_to` association creates a one-to-one match with another model. In d #### Methods Added by `belongs_to` -When you declare a `belongs_to` association, the declaring class automatically gains five methods related to the association: +When you declare a `belongs_to` association, the declaring class automatically gains 6 methods related to the association: * `association` * `association=(associate)` @@ -906,7 +889,7 @@ The `belongs_to` association supports these options: ##### `:autosave` -If you set the `:autosave` option to `true`, Rails will save any loaded members and destroy members that are marked for destruction whenever you save the parent object. +If you set the `:autosave` option to `true`, Rails will save any loaded association members and destroy members that are marked for destruction whenever you save the parent object. Setting `:autosave` to `false` is not the same as not setting the `:autosave` option. If the `:autosave` option is not present, then new associated objects will be saved, but updated associated objects will not be saved. ##### `:class_name` @@ -1012,7 +995,7 @@ When we execute `@user.todos.create` then the `@todo` record will have its ##### `:inverse_of` -The `:inverse_of` option specifies the name of the `has_many` or `has_one` association that is the inverse of this association. Does not work in combination with the `:polymorphic` options. +The `:inverse_of` option specifies the name of the `has_many` or `has_one` association that is the inverse of this association. ```ruby class Author < ApplicationRecord @@ -1082,7 +1065,7 @@ You can use any of the standard [querying methods](active_record_querying.html) The `where` method lets you specify the conditions that the associated object must meet. ```ruby -class book < ApplicationRecord +class Book < ApplicationRecord belongs_to :author, -> { where active: true } end ``` @@ -1155,7 +1138,7 @@ The `has_one` association creates a one-to-one match with another model. In data #### Methods Added by `has_one` -When you declare a `has_one` association, the declaring class automatically gains five methods related to the association: +When you declare a `has_one` association, the declaring class automatically gains 6 methods related to the association: * `association` * `association=(associate)` @@ -1257,7 +1240,7 @@ Setting the `:as` option indicates that this is a polymorphic association. Polym ##### `:autosave` -If you set the `:autosave` option to `true`, Rails will save any loaded members and destroy members that are marked for destruction whenever you save the parent object. +If you set the `:autosave` option to `true`, Rails will save any loaded association members and destroy members that are marked for destruction whenever you save the parent object. Setting `:autosave` to `false` is not the same as not setting the `:autosave` option. If the `:autosave` option is not present, then new associated objects will be saved, but updated associated objects will not be saved. ##### `:class_name` @@ -1299,7 +1282,7 @@ TIP: In any case, Rails will not create foreign key columns for you. You need to ##### `:inverse_of` -The `:inverse_of` option specifies the name of the `belongs_to` association that is the inverse of this association. Does not work in combination with the `:through` or `:as` options. +The `:inverse_of` option specifies the name of the `belongs_to` association that is the inverse of this association. ```ruby class Supplier < ApplicationRecord @@ -1428,7 +1411,7 @@ The `has_many` association creates a one-to-many relationship with another model #### Methods Added by `has_many` -When you declare a `has_many` association, the declaring class automatically gains 16 methods related to the association: +When you declare a `has_many` association, the declaring class automatically gains 17 methods related to the association: * `collection` * `collection<<(object, ...)` @@ -1561,7 +1544,8 @@ The `collection.size` method returns the number of objects in the collection. ##### `collection.find(...)` -The `collection.find` method finds objects within the collection. It uses the same syntax and options as `ActiveRecord::Base.find`. +The `collection.find` method finds objects within the collection. It uses the same syntax and options as +[`ActiveRecord::Base.find`](http://api.rubyonrails.org/classes/ActiveRecord/FinderMethods.html#method-i-find). ```ruby @available_book = @author.books.find(1) @@ -1653,7 +1637,7 @@ Setting the `:as` option indicates that this is a polymorphic association, as di ##### `:autosave` -If you set the `:autosave` option to `true`, Rails will save any loaded members and destroy members that are marked for destruction whenever you save the parent object. +If you set the `:autosave` option to `true`, Rails will save any loaded association members and destroy members that are marked for destruction whenever you save the parent object. Setting `:autosave` to `false` is not the same as not setting the `:autosave` option. If the `:autosave` option is not present, then new associated objects will be saved, but updated associated objects will not be saved. ##### `:class_name` @@ -1693,7 +1677,7 @@ TIP: In any case, Rails will not create foreign key columns for you. You need to ##### `:inverse_of` -The `:inverse_of` option specifies the name of the `belongs_to` association that is the inverse of this association. Does not work in combination with the `:through` or `:as` options. +The `:inverse_of` option specifies the name of the `belongs_to` association that is the inverse of this association. ```ruby class Author < ApplicationRecord @@ -1960,7 +1944,7 @@ The `has_and_belongs_to_many` association creates a many-to-many relationship wi #### Methods Added by `has_and_belongs_to_many` -When you declare a `has_and_belongs_to_many` association, the declaring class automatically gains 16 methods related to the association: +When you declare a `has_and_belongs_to_many` association, the declaring class automatically gains 17 methods related to the association: * `collection` * `collection<<(object, ...)` @@ -2091,7 +2075,8 @@ The `collection.size` method returns the number of objects in the collection. ##### `collection.find(...)` -The `collection.find` method finds objects within the collection. It uses the same syntax and options as `ActiveRecord::Base.find`. It also adds the additional condition that the object must be in the collection. +The `collection.find` method finds objects within the collection. It uses the same syntax and options as +[`ActiveRecord::Base.find`](http://api.rubyonrails.org/classes/ActiveRecord/FinderMethods.html#method-i-find). ```ruby @assembly = @part.assemblies.find(1) @@ -2099,7 +2084,7 @@ The `collection.find` method finds objects within the collection. It uses the sa ##### `collection.where(...)` -The `collection.where` method finds objects within the collection based on the conditions supplied but the objects are loaded lazily meaning that the database is queried only when the object(s) are accessed. It also adds the additional condition that the object must be in the collection. +The `collection.where` method finds objects within the collection based on the conditions supplied but the objects are loaded lazily meaning that the database is queried only when the object(s) are accessed. ```ruby @new_assemblies = @part.assemblies.where("created_at > ?", 2.days.ago) @@ -2176,7 +2161,7 @@ end ##### `:autosave` -If you set the `:autosave` option to `true`, Rails will save any loaded members and destroy members that are marked for destruction whenever you save the parent object. +If you set the `:autosave` option to `true`, Rails will save any loaded association members and destroy members that are marked for destruction whenever you save the parent object. Setting `:autosave` to `false` is not the same as not setting the `:autosave` option. If the `:autosave` option is not present, then new associated objects will be saved, but updated associated objects will not be saved. ##### `:class_name` @@ -2406,7 +2391,7 @@ 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 +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. |