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Diffstat (limited to 'guides/source/association_basics.md')
| -rw-r--r-- | guides/source/association_basics.md | 42 |
1 files changed, 26 insertions, 16 deletions
diff --git a/guides/source/association_basics.md b/guides/source/association_basics.md index d7277b487f..8ef982f8c5 100644 --- a/guides/source/association_basics.md +++ b/guides/source/association_basics.md @@ -40,7 +40,7 @@ end @customer.destroy ``` -With Active Record associations, we can streamline these — and other — operations by declaratively telling Rails that there is a connection between the two models. Here's the revised code for setting up customers and orders: +With Active Record associations, we can streamline these - and other - operations by declaratively telling Rails that there is a connection between the two models. Here's the revised code for setting up customers and orders: ```ruby class Customer < ActiveRecord::Base @@ -69,7 +69,7 @@ To learn more about the different types of associations, read the next section o The Types of Associations ------------------------- -In Rails, an _association_ is a connection between two Active Record models. Associations are implemented using macro-style calls, so that you can declaratively add features to your models. For example, by declaring that one model `belongs_to` another, you instruct Rails to maintain Primary Key–Foreign Key information between instances of the two models, and you also get a number of utility methods added to your model. Rails supports six types of associations: +In Rails, an _association_ is a connection between two Active Record models. Associations are implemented using macro-style calls, so that you can declaratively add features to your models. For example, by declaring that one model `belongs_to` another, you instruct Rails to maintain Primary Key-Foreign Key information between instances of the two models, and you also get a number of utility methods added to your model. Rails supports six types of associations: * `belongs_to` * `has_one` @@ -261,7 +261,10 @@ With `through: :sections` specified, Rails will now understand: ### The `has_one :through` Association -A `has_one :through` association sets up a one-to-one connection with another model. This association indicates that the declaring model can be matched with one instance of another model by proceeding _through_ a third model. For example, if each supplier has one account, and each account is associated with one account history, then the customer model could look like this: +A `has_one :through` association sets up a one-to-one connection with another model. This association indicates +that the declaring model can be matched with one instance of another model by proceeding _through_ a third model. +For example, if each supplier has one account, and each account is associated with one account history, then the +supplier model could look like this: ```ruby class Supplier < ActiveRecord::Base @@ -781,7 +784,7 @@ The `create_association` method returns a new object of the associated type. Thi ##### `create_association!(attributes = {})` -Does the same as <tt>create_association</tt> above, but raises <tt>ActiveRecord::RecordInvalid</tt> if the record is invalid. +Does the same as `create_association` above, but raises `ActiveRecord::RecordInvalid` if the record is invalid. #### Options for `belongs_to` @@ -953,7 +956,7 @@ end ##### `includes` -You can use the `includes` method let you specify second-order associations that should be eager-loaded when this association is used. For example, consider these models: +You can use the `includes` method to specify second-order associations that should be eager-loaded when this association is used. For example, consider these models: ```ruby class LineItem < ActiveRecord::Base @@ -1083,7 +1086,7 @@ The `create_association` method returns a new object of the associated type. Thi ##### `create_association!(attributes = {})` -Does the same as <tt>create_association</tt> above, but raises <tt>ActiveRecord::RecordInvalid</tt> if the record is invalid. +Does the same as `create_association` above, but raises `ActiveRecord::RecordInvalid` if the record is invalid. #### Options for `has_one` @@ -1137,6 +1140,12 @@ Controls what happens to the associated object when its owner is destroyed: * `: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 +It's necessary not to set or leave `:nullify` option for those associations +that have `NOT NULL` database constraints. If you don't set `dependent` to +destroy such associations you won't be able to change the associated object +because initial associated object foreign key will be set to unallowed `NULL` +value. + ##### `: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: @@ -1443,7 +1452,7 @@ The `collection.create` method returns a new object of the associated type. This ##### `collection.create!(attributes = {})` -Does the same as <tt>collection.create</tt> above, but raises <tt>ActiveRecord::RecordInvalid</tt> if the record is invalid. +Does the same as `collection.create` above, but raises `ActiveRecord::RecordInvalid` if the record is invalid. #### Options for `has_many` @@ -1736,15 +1745,15 @@ If you want to make sure that, upon insertion, all of the records in the persisted association are distinct (so that you can be sure that when you inspect the association that you will never find duplicate records), you should add a unique index on the table itself. For example, if you have a table named -``person_posts`` and you want to make sure all the posts are unique, you could +`person_posts` and you want to make sure all the posts are unique, you could add the following in a migration: ```ruby -add_index :person_posts, :post, :unique => true +add_index :person_posts, :post, unique: true ``` -Note that checking for uniqueness using something like ``include?`` is subject -to race conditions. Do not attempt to use ``include?`` to enforce distinctness +Note that checking for uniqueness using something like `include?` is subject +to race conditions. Do not attempt to use `include?` to enforce distinctness in an association. For instance, using the post example from above, the following code would be racy because multiple users could be attempting this at the same time: @@ -1936,7 +1945,7 @@ The `collection.create` method returns a new object of the associated type. This ##### `collection.create!(attributes = {})` -Does the same as <tt>collection.create</tt>, but raises <tt>ActiveRecord::RecordInvalid</tt> if the record is invalid. +Does the same as `collection.create`, but raises `ActiveRecord::RecordInvalid` if the record is invalid. #### Options for `has_and_belongs_to_many` @@ -1944,8 +1953,8 @@ While Rails uses intelligent defaults that will work well in most situations, th ```ruby class Parts < ActiveRecord::Base - has_and_belongs_to_many :assemblies, uniq: true, - read_only: true + has_and_belongs_to_many :assemblies, autosave: true, + readonly: true end ``` @@ -1957,6 +1966,7 @@ The `has_and_belongs_to_many` association supports these options: * `:foreign_key` * `:join_table` * `:validate` +* `:readonly` ##### `:association_foreign_key` @@ -2171,7 +2181,7 @@ You're not limited to the functionality that Rails automatically builds into ass class Customer < ActiveRecord::Base has_many :orders do def find_by_order_prefix(order_number) - find_by_region_id(order_number[0..2]) + find_by(region_id: order_number[0..2]) end end end @@ -2199,4 +2209,4 @@ 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`.
\ No newline at end of file +* `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`. |