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Diffstat (limited to 'guides/source/association_basics.md')
| -rw-r--r-- | guides/source/association_basics.md | 53 |
1 files changed, 18 insertions, 35 deletions
diff --git a/guides/source/association_basics.md b/guides/source/association_basics.md index b5e236b790..f895cadea5 100644 --- a/guides/source/association_basics.md +++ b/guides/source/association_basics.md @@ -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)` @@ -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)` @@ -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, ...)` @@ -1694,7 +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 @@ -1961,7 +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, ...)` |