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Diffstat (limited to 'railties/guides/source/association_basics.textile')
| -rw-r--r-- | railties/guides/source/association_basics.textile | 65 |
1 files changed, 27 insertions, 38 deletions
diff --git a/railties/guides/source/association_basics.textile b/railties/guides/source/association_basics.textile index ce4ff0389d..451653655f 100644 --- a/railties/guides/source/association_basics.textile +++ b/railties/guides/source/association_basics.textile @@ -211,7 +211,7 @@ end h4. Choosing Between +belongs_to+ and +has_one+ -If you want to set up a 1–1 relationship between two models, you'll need to add +belongs_to+ to one, and +has_one+ to the other. How do you know which is which? +If you want to set up a one-to-one relationship between two models, you'll need to add +belongs_to+ to one, and +has_one+ to the other. How do you know which is which? The distinction is in where you place the foreign key (it goes on the table for the class declaring the +belongs_to+ association), but you should give some thought to the actual meaning of the data as well. The +has_one+ relationship says that one of something is yours - that is, that something points back to you. For example, it makes more sense to say that a supplier owns an account than that an account owns a supplier. This suggests that the correct relationships are like this: @@ -566,7 +566,7 @@ The <tt>build_<em>association</em></tt> method returns a new object of the assoc h6(#belongs_to-create_association). <tt>create_<em>association</em>(attributes = {})</tt> -The <tt>create_<em>association</em></tt> method returns a new object of the associated type. This object will be instantiated from the passed attributes, and the link through this object's foreign key will be set. In addition, the associated object _will_ be saved (assuming that it passes any validations). +The <tt>create_<em>association</em></tt> method returns a new object of the associated type. This object will be instantiated from the passed attributes, the link through this object's foreign key will be set, and, once it passes all of the validations specified on the associated model, the associated object _will_ be saved. <ruby> @customer = @order.create_customer(:customer_number => 123, @@ -576,7 +576,7 @@ The <tt>create_<em>association</em></tt> method returns a new object of the asso h5. Options for +belongs_to+ -In many situations, you can use the default behavior of +belongs_to+ without any customization. But despite Rails' emphasis of convention over customization, you can alter that behavior in a number of ways. This section covers the options that you can pass when you create a +belongs_to+ association. For example, an association with several options might look like this: +While Rails uses intelligent defaults that will work well in most situations, there may be times when you want to customize the behavior of the +belongs_to+ association reference. Such customizations can easily be accomplished by passing options when you create the association. For example, this assocation uses two such options: <ruby> class Order < ActiveRecord::Base @@ -671,7 +671,7 @@ WARNING: You should not specify this option on a +belongs_to+ association that i h6(#belongs_to-foreign_key). +:foreign_key+ -By convention, Rails guesses that the column used to hold the foreign key on this model is the name of the association with the suffix +_id+ added. The +:foreign_key+ option lets you set the name of the foreign key directly: +By convention, Rails assumes that the column used to hold the foreign key on this model is the name of the association with the suffix +_id+ added. The +:foreign_key+ option lets you set the name of the foreign key directly: <ruby> class Order < ActiveRecord::Base @@ -760,9 +760,9 @@ h6(#belongs_to-validate). +:validate+ If you set the +:validate+ option to +true+, then associated objects will be validated whenever you save this object. By default, this is +false+: associated objects will not be validated when this object is saved. -h5(#belongs_to-how_to_know_whether_theres_an_associated_object). How To Know Whether There's an Associated Object? +h5(#belongs_to-do_any_associated_objects_exist). Do Any Associated Objects Exist? -To know whether there's and associated object just check <tt><em>association</em>.nil?</tt>: +You can see if any associated objects exist by using the <tt><em>association</em>.nil?</tt> method: <ruby> if @order.customer.nil? @@ -834,7 +834,7 @@ The <tt>build_<em>association</em></tt> method returns a new object of the assoc h6(#has_one-create_association). <tt>create_<em>association</em>(attributes = {})</tt> -The <tt>create_<em>association</em></tt> method returns a new object of the associated type. This object will be instantiated from the passed attributes, and the link through its foreign key will be set. In addition, the associated object _will_ be saved (assuming that it passes any validations). +The <tt>create_<em>association</em></tt> 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 set, and, once it passes all of the validations specified on the associated model, the associated object _will_ be saved. <ruby> @account = @supplier.create_account(:terms => "Net 30") @@ -842,7 +842,7 @@ The <tt>create_<em>association</em></tt> method returns a new object of the asso h5. Options for +has_one+ -In many situations, you can use the default behavior of +has_one+ without any customization. But despite Rails' emphasis of convention over customization, you can alter that behavior in a number of ways. This section covers the options that you can pass when you create a +has_one+ association. For example, an association with several options might look like this: +While Rails uses intelligent defaults that will work well in most situations, there may be times when you want to customize the behavior of the +has_one+ association reference. Such customizations can easily be accomplished by passing options when you create the association. For example, this assocation uses two such options: <ruby> class Supplier < ActiveRecord::Base @@ -902,7 +902,7 @@ If you set the +:dependent+ option to +:destroy+, then deleting this object will h6(#has_one-foreign_key). +:foreign_key+ -By convention, Rails guesses 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: +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: <ruby> class Supplier < ActiveRecord::Base @@ -954,7 +954,7 @@ The +:order+ option dictates the order in which associated objects will be recei h6(#has_one-primary_key). +:primary_key+ -By convention, Rails guesses that the column used to hold the primary key of this model is +id+. You can override this and explicitly specify the primary key with the +:primary_key+ option. +By convention, Rails assumes that the column used to hold the primary key of this model is +id+. You can override this and explicitly specify the primary key with the +:primary_key+ option. h6(#has_one-readonly). +:readonly+ @@ -980,9 +980,9 @@ h6(#has_one-validate). +:validate+ If you set the +:validate+ option to +true+, then associated objects will be validated whenever you save this object. By default, this is +false+: associated objects will not be validated when this object is saved. -h5(#has_one-how_to_know_whether_theres_an_associated_object). How To Know Whether There's an Associated Object? +h5(#has_one-do_any_associated_objects_exist). Do Any Associated Objects Exist? -To know whether there's and associated object just check <tt><em>association</em>.nil?</tt>: +You can see if any associated objects exist by using the <tt><em>association</em>.nil?</tt> method: <ruby> if @supplier.account.nil? @@ -1147,7 +1147,7 @@ The <tt><em>collection</em>.build</tt> method returns one or more new objects of h6(#has_many-collection-create). <tt><em>collection</em>.create(attributes = {})</tt> -The <tt><em>collection</em>.create</tt> 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 the associated object _will_ be saved (assuming that it passes any validations). +The <tt><em>collection</em>.create</tt> 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. <ruby> @order = @customer.orders.create(:order_date => Time.now, @@ -1156,7 +1156,7 @@ The <tt><em>collection</em>.create</tt> method returns a new object of the assoc h5. Options for +has_many+ -In many situations, you can use the default behavior for +has_many+ without any customization. But you can alter that behavior in a number of ways. This section covers the options that you can pass when you create a +has_many+ association. For example, an association with several options might look like this: +While Rails uses intelligent defaults that will work well in most situations, there may be times when you want to customize the behavior of the +has_many+ association reference. Such customizations can easily be accomplished by passing options when you create the association. For example, this assocation uses two such options: <ruby> class Customer < ActiveRecord::Base @@ -1229,17 +1229,15 @@ end If you use a hash-style +:conditions+ option, then record creation via this association will be automatically scoped using the hash. In this case, using +@customer.confirmed_orders.create+ or +@customer.confirmed_orders.build+ will create orders where the confirmed column has the value +true+. -If you need to evaluate conditions dynamically at runtime, you could use string interpolation in single quotes: +If you need to evaluate conditions dynamically at runtime, use a proc: <ruby> class Customer < ActiveRecord::Base has_many :latest_orders, :class_name => "Order", - :conditions => 'orders.created_at > #{10.hours.ago.to_s(:db).inspect}' + :conditions => proc { ["orders.created_at > ?, 10.hours.ago] } end </ruby> -Be sure to use single quotes. - h6(#has_many-counter_sql). +:counter_sql+ Normally Rails automatically generates the proper SQL to count the association members. With the +:counter_sql+ option, you can specify a complete SQL statement to count them yourself. @@ -1262,7 +1260,7 @@ Normally Rails automatically generates the proper SQL to fetch the association m h6(#has_many-foreign_key). +:foreign_key+ -By convention, Rails guesses 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: +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: <ruby> class Customer < ActiveRecord::Base @@ -1345,7 +1343,7 @@ end h6(#has_many-primary_key). +:primary_key+ -By convention, Rails guesses that the column used to hold the primary key of the association is +id+. You can override this and explicitly specify the primary key with the +:primary_key+ option. +By convention, Rails assumes that the column used to hold the primary key of the association is +id+. You can override this and explicitly specify the primary key with the +:primary_key+ option. h6(#has_many-readonly). +:readonly+ @@ -1551,7 +1549,7 @@ The <tt><em>collection</em>.find</tt> method finds objects within the collection :conditions => ["created_at > ?", 2.days.ago]) </ruby> -NOTE: Starting Rails 3, supplying options to +ActiveRecord::Base.find+ method is discouraged. Use <tt><em>collection</em>.where</tt> instead when you need to pass conditions. +NOTE: Beginning with Rails 3, supplying options to the +ActiveRecord::Base.find+ method is discouraged. Use <tt><em>collection</em>.where</tt> instead when you need to pass conditions. h6(#has_and_belongs_to_many-collection-where). <tt><em>collection</em>.where(...)</tt> @@ -1576,7 +1574,7 @@ The <tt><em>collection</em>.build</tt> method returns a new object of the associ h6(#has_and_belongs_to_many-create-attributes). <tt><em>collection</em>.create(attributes = {})</tt> -The <tt><em>collection</em>.create</tt> method returns a new object of the associated type. This object will be instantiated from the passed attributes, the link through the join table will be created, and the associated object _will_ be saved (assuming that it passes any validations). +The <tt><em>collection</em>.create</tt> method returns a new object of the associated type. This object will be instantiated from the passed attributes, the link through the join table will be created, and, once it passes all of the validations specified on the associated model, the associated object _will_ be saved. <ruby> @assembly = @part.assemblies.create( @@ -1585,7 +1583,7 @@ The <tt><em>collection</em>.create</tt> method returns a new object of the assoc h5. Options for +has_and_belongs_to_many+ -In many situations, you can use the default behavior for +has_and_belongs_to_many+ without any customization. But you can alter that behavior in a number of ways. This section covers the options that you can pass when you create a +has_and_belongs_to_many+ association. For example, an association with several options might look like this: +While Rails uses intelligent defaults that will work well in most situations, there may be times when you want to customize the behavior of the +has_and_belongs_to_many+ association reference. Such customizations can easily be accomplished by passing options when you create the association. For example, this assocation uses two such options: <ruby> class Parts < ActiveRecord::Base @@ -1619,7 +1617,7 @@ The +has_and_belongs_to_many+ association supports these options: h6(#has_and_belongs_to_many-association_foreign_key). +:association_foreign_key+ -By convention, Rails guesses that the column in the join table used to hold the foreign key pointing to the other model is the name of that model with the suffix +_id+ added. The +:association_foreign_key+ option lets you set the name of the foreign key directly: +By convention, Rails assumes that the column in the join table used to hold the foreign key pointing to the other model is the name of that model with the suffix +_id+ added. The +:association_foreign_key+ option lets you set the name of the foreign key directly: TIP: The +:foreign_key+ and +:association_foreign_key+ options are useful when setting up a many-to-many self-join. For example: @@ -1687,7 +1685,7 @@ Normally Rails automatically generates the proper SQL to fetch the association m h6(#has_and_belongs_to_many-foreign_key). +:foreign_key+ -By convention, Rails guesses that the column in the join table used to hold the foreign key pointing to this 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: +By convention, Rails assumes that the column in the join table used to hold the foreign key pointing to this 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: <ruby> class User < ActiveRecord::Base @@ -1855,17 +1853,8 @@ class Customer < ActiveRecord::Base end </ruby> -Extensions can refer to the internals of the association proxy using these three accessors: - -* +proxy_owner+ returns the object that the association is a part of. -* +proxy_reflection+ returns the reflection object that describes the association. -* +proxy_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+. - -h3. Changelog +Extensions can refer to the internals of the association proxy using these three attributes of the +proxy_association+ accessor: -* April 7, 2010: Fixed document to validate XHTML 1.0 Strict. "Jaime Iniesta":http://jaimeiniesta.com -* April 19, 2009: Added +:touch+ option to +belongs_to+ associations by "Mike Gunderloy":credits.html#mgunderloy -* February 1, 2009: Added +:autosave+ option "Mike Gunderloy":credits.html#mgunderloy -* September 28, 2008: Corrected +has_many :through+ diagram, added polymorphic diagram, some reorganization by "Mike Gunderloy":credits.html#mgunderloy . First release version. -* September 22, 2008: Added diagrams, misc. cleanup by "Mike Gunderloy":credits.html#mgunderloy (not yet approved for publication) -* September 14, 2008: initial version by "Mike Gunderloy":credits.html#mgunderloy (not yet approved for publication) +* +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+. |