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Diffstat (limited to 'guides/source/association_basics.md')
| -rw-r--r-- | guides/source/association_basics.md | 70 |
1 files changed, 52 insertions, 18 deletions
diff --git a/guides/source/association_basics.md b/guides/source/association_basics.md index 5c96a53d09..74cd9bdc7b 100644 --- a/guides/source/association_basics.md +++ b/guides/source/association_basics.md @@ -622,6 +622,19 @@ end We pass `id: false` to `create_table` because that table does not represent a model. That's required for the association to work properly. If you observe any strange behavior in a `has_and_belongs_to_many` association like mangled model IDs, or exceptions about conflicting IDs, chances are you forgot that bit. +You can also use the method `create_join_table` + +```ruby +class CreateAssembliesPartsJoinTable < ActiveRecord::Migration + def change + create_join_table :assemblies, :parts do |t| + t.index :assembly_id + t.index :part_id + end + end +end +``` + ### Controlling Association Scope By default, associations look for objects only within the current module's scope. This can be important when you declare Active Record models within a module. For example: @@ -755,7 +768,7 @@ The `belongs_to` association creates a one-to-one match with another model. In d When you declare a `belongs_to` association, the declaring class automatically gains five methods related to the association: -* `association(force_reload = false)` +* `association` * `association=(associate)` * `build_association(attributes = {})` * `create_association(attributes = {})` @@ -781,7 +794,7 @@ create_customer! NOTE: When initializing a new `has_one` or `belongs_to` association you must use the `build_` prefix to build the association, rather than the `association.build` method that would be used for `has_many` or `has_and_belongs_to_many` associations. To create one, use the `create_` prefix. -##### `association(force_reload = false)` +##### `association` The `association` method returns the associated object, if any. If no associated object is found, it returns `nil`. @@ -789,7 +802,11 @@ The `association` method returns the associated object, if any. If no associated @customer = @order.customer ``` -If the associated object has already been retrieved from the database for this object, the cached version will be returned. To override this behavior (and force a database read), pass `true` as the `force_reload` argument. +If the associated object has already been retrieved from the database for this object, the cached version will be returned. To override this behavior (and force a database read), call `#reload` on the parent object. + +```ruby +@customer = @order.reload.customer +``` ##### `association=(associate)` @@ -915,8 +932,11 @@ If you set the `:dependent` option to: * `:destroy`, when the object is destroyed, `destroy` will be called on its associated objects. -* `:delete`, when the object is destroyed, all its associated objects will be +* `:delete_all`, when the object is destroyed, all its associated objects will be deleted directly from the database without calling their `destroy` method. +* `:nullify`, causes the foreign key to be set to `NULL`. Callbacks are not executed. +* `:restrict_with_exception`, causes an exception to be raised if there is an associated record +* `:restrict_with_error`, causes an error to be added to the owner if there is an associated object WARNING: You should not specify this option on a `belongs_to` association that is connected with a `has_many` association on the other class. Doing so can lead to orphaned records in your database. @@ -1100,7 +1120,7 @@ The `has_one` association creates a one-to-one match with another model. In data When you declare a `has_one` association, the declaring class automatically gains five methods related to the association: -* `association(force_reload = false)` +* `association` * `association=(associate)` * `build_association(attributes = {})` * `create_association(attributes = {})` @@ -1126,7 +1146,7 @@ create_account! NOTE: When initializing a new `has_one` or `belongs_to` association you must use the `build_` prefix to build the association, rather than the `association.build` method that would be used for `has_many` or `has_and_belongs_to_many` associations. To create one, use the `create_` prefix. -##### `association(force_reload = false)` +##### `association` The `association` method returns the associated object, if any. If no associated object is found, it returns `nil`. @@ -1134,7 +1154,11 @@ The `association` method returns the associated object, if any. If no associated @account = @supplier.account ``` -If the associated object has already been retrieved from the database for this object, the cached version will be returned. To override this behavior (and force a database read), pass `true` as the `force_reload` argument. +If the associated object has already been retrieved from the database for this object, the cached version will be returned. To override this behavior (and force a database read), call `#reload` on the parent object. + +```ruby +@account = @supplier.reload.account +``` ##### `association=(associate)` @@ -1367,7 +1391,7 @@ The `has_many` association creates a one-to-many relationship with another model When you declare a `has_many` association, the declaring class automatically gains 16 methods related to the association: -* `collection(force_reload = false)` +* `collection` * `collection<<(object, ...)` * `collection.delete(object, ...)` * `collection.destroy(object, ...)` @@ -1395,7 +1419,7 @@ end Each instance of the `Customer` model will have these methods: ```ruby -orders(force_reload = false) +orders orders<<(object, ...) orders.delete(object, ...) orders.destroy(object, ...) @@ -1413,7 +1437,7 @@ orders.create(attributes = {}) orders.create!(attributes = {}) ``` -##### `collection(force_reload = false)` +##### `collection` The `collection` method returns an array of all of the associated objects. If there are no associated objects, it returns an empty array. @@ -1519,20 +1543,30 @@ conditions exists in the collection. It uses the same syntax and options as ##### `collection.build(attributes = {}, ...)` -The `collection.build` method returns one or more new objects of the associated type. These objects will be instantiated from the passed attributes, and the link through their foreign key will be created, but the associated objects will _not_ yet be saved. +The `collection.build` method returns a single or array of new objects of the associated type. The object(s) will be instantiated from the passed attributes, and the link through their foreign key will be created, but the associated objects will _not_ yet be saved. ```ruby @order = @customer.orders.build(order_date: Time.now, order_number: "A12345") + +@orders = @customer.orders.build([ + { order_date: Time.now, order_number: "A12346" }, + { order_date: Time.now, order_number: "A12347" } +]) ``` ##### `collection.create(attributes = {})` -The `collection.create` method returns a new object of the associated type. This object will be instantiated from the passed attributes, the link through its foreign key will be created, and, once it passes all of the validations specified on the associated model, the associated object _will_ be saved. +The `collection.create` method returns a single or array of new objects of the associated type. The object(s) will be instantiated from the passed attributes, the link through its foreign key will be created, and, once it passes all of the validations specified on the associated model, the associated object _will_ be saved. ```ruby @order = @customer.orders.create(order_date: Time.now, order_number: "A12345") + +@orders = @customer.orders.create([ + { order_date: Time.now, order_number: "A12346" }, + { order_date: Time.now, order_number: "A12347" } +]) ``` ##### `collection.create!(attributes = {})` @@ -1869,7 +1903,7 @@ The `has_and_belongs_to_many` association creates a many-to-many relationship wi When you declare a `has_and_belongs_to_many` association, the declaring class automatically gains 16 methods related to the association: -* `collection(force_reload = false)` +* `collection` * `collection<<(object, ...)` * `collection.delete(object, ...)` * `collection.destroy(object, ...)` @@ -1897,7 +1931,7 @@ end Each instance of the `Part` model will have these methods: ```ruby -assemblies(force_reload = false) +assemblies assemblies<<(object, ...) assemblies.delete(object, ...) assemblies.destroy(object, ...) @@ -1922,7 +1956,7 @@ If the join table for a `has_and_belongs_to_many` association has additional col WARNING: The use of extra attributes on the join table in a `has_and_belongs_to_many` association is deprecated. If you require this sort of complex behavior on the table that joins two models in a many-to-many relationship, you should use a `has_many :through` association instead of `has_and_belongs_to_many`. -##### `collection(force_reload = false)` +##### `collection` The `collection` method returns an array of all of the associated objects. If there are no associated objects, it returns an empty array. @@ -2129,7 +2163,7 @@ You can use any of the standard [querying methods](active_record_querying.html) * `order` * `readonly` * `select` -* `uniq` +* `distinct` ##### `where` @@ -2205,9 +2239,9 @@ If you use the `readonly` method, then the associated objects will be read-only The `select` method lets you override the SQL `SELECT` clause that is used to retrieve data about the associated objects. By default, Rails retrieves all columns. -##### `uniq` +##### `distinct` -Use the `uniq` method to remove duplicates from the collection. +Use the `distinct` method to remove duplicates from the collection. #### When are Objects Saved? |