From fd9d92a14198f1774e99087b18c19b5b6a6872d9 Mon Sep 17 00:00:00 2001
From: Mike Gunderloy <MikeG1@larkfarm.com>
Date: Sun, 28 Sep 2008 08:34:46 -0500
Subject: Image updates & reorganization. First release version.
---
.../doc/guides/activerecord/association_basics.txt | 387 +++++++++++++--------
.../activerecord/images/has_many_through.png | Bin 112630 -> 100220 bytes
.../doc/guides/activerecord/images/polymorphic.png | Bin 0 -> 85248 bytes
3 files changed, 238 insertions(+), 149 deletions(-)
create mode 100644 railties/doc/guides/activerecord/images/polymorphic.png
(limited to 'railties/doc/guides')
diff --git a/railties/doc/guides/activerecord/association_basics.txt b/railties/doc/guides/activerecord/association_basics.txt
index d33c0ac3cf..00402d5eda 100644
--- a/railties/doc/guides/activerecord/association_basics.txt
+++ b/railties/doc/guides/activerecord/association_basics.txt
@@ -345,6 +345,8 @@ class CreatePictures < ActiveRecord::Migration
end
-------------------------------------------------------
+image:images/polymorphic.png[Polymorphic Association Diagram]
+
=== Self Joins
In designing a data model, you will sometimes find a model that should have a relation to itself. For example, you may want to store all employees in a single database model, but be able to trace relationships such as manager and subordinates. This situation can be modeled with self-joining associations:
@@ -614,6 +616,24 @@ class Order < ActiveRecord::Base
end
-------------------------------------------------------
+The +belongs_to+ association supports these options:
+
+* +:accessible+
+* +:class_name+
+* +:conditions+
+* +:counter_cache+
+* +:dependent+
+* +:foreign_key+
+* +:include+
+* +:polymorphic+
+* +:readonly+
+* +:select+
+* +:validate+
+
+===== +:accessible+
+
+The +:accessible+ option is the association version of +ActiveRecord::Base#attr_accessible+. If you set the +:accessible+ option to true, then mass assignment is allowed for this association.
+
===== +:class_name+
If the name of the other model cannot be derived from the association name, you can use the +:class_name+ option to supply the model name. For example, if an order belongs to a customer, but the actual name of the model containing customers is patron, you'd set things up this way:
@@ -636,29 +656,6 @@ class Order < ActiveRecord::Base
end
-------------------------------------------------------
-===== +:select+
-
-The +:select+ option lets you override the SQL +SELECT+ clause that is used to retrieve data about the associated object. By default, Rails retrieves all columns.
-
-===== +: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:
-
-[source, ruby]
--------------------------------------------------------
-class Order < ActiveRecord::Base
- belongs_to :customer, :class_name => :patron, :foreign_key => "patron_id"
-end
--------------------------------------------------------
-
-TIP: In any case, Rails will not create foreign key columns for you. You need to explicitly define them as part of your migrations.
-
-===== +:dependent+
-
-If you set the +:dependent+ option to +:destroy+, then deleting this object will call the destroy method on the associated object to delete that object. If you set the +:dependent+ option to +:delete+, then deleting this object will delete the associated object _without_ calling its +destroy+ method.
-
-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.
-
===== +:counter_cache+
The +:counter_cache+ option can be used to make finding the number of belonging objects more efficient. Consider these models:
@@ -703,6 +700,25 @@ Counter cache columns are added to the containing model's list of read-only attr
WARNING: When you create a counter cache column in the database, be sure to specify a default value of zero. Otherwise, Rails will not properly maintain the counter.
+===== +:dependent+
+
+If you set the +:dependent+ option to +:destroy+, then deleting this object will call the destroy method on the associated object to delete that object. If you set the +:dependent+ option to +:delete+, then deleting this object will delete the associated object _without_ calling its +destroy+ method.
+
+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.
+
+===== +: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:
+
+[source, ruby]
+-------------------------------------------------------
+class Order < ActiveRecord::Base
+ belongs_to :customer, :class_name => :patron, :foreign_key => "patron_id"
+end
+-------------------------------------------------------
+
+TIP: In any case, Rails will not create foreign key columns for you. You need to explicitly define them as part of your migrations.
+
===== +:include+
You can use the :include option to specify second-order associations that should be eager-loaded when this association is used. For example, consider these models:
@@ -747,15 +763,16 @@ Passing +true+ to the +:polymorphic+ option indicates that this is a polymorphic
If you set the +:readonly+ option to +true+, then the associated object will be read-only when retrieved via the association.
-===== +:validate+
+===== +:select+
-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.
+The +:select+ option lets you override the SQL +SELECT+ clause that is used to retrieve data about the associated object. By default, Rails retrieves all columns.
-===== +:accessible+
+===== +:validate+
-The +:accessible+ option is the association version of +ActiveRecord::Base#attr_accessible+. If you set the +:accessible+ option to true, then mass assignment is allowed for this association.
+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.
==== When are Objects Saved?
+
Assigning an object to a +belongs_to+ association does _not_ automatically save the object. It does not save the associated object either.
=== The has_one Association
@@ -843,7 +860,6 @@ The +create__\_association__+ method returns a new object of the associated type
==== 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:
[source, ruby]
@@ -853,6 +869,32 @@ class Supplier < ActiveRecord::Base
end
-------------------------------------------------------
+The +has_one+ association supports these options:
+
+* +:accessible+
+* +:as+
+* +:class_name+
+* +:conditions+
+* +:dependent+
+* +:foreign_key+
+* +:include+
+* +:order+
+* +:primary_key+
+* +:readonly+
+* +:select+
+* +:source+
+* +:source_type+
+* +:through+
+* +:validate+
+
+===== +:accessible+
+
+The +:accessible+ option is the association version of +ActiveRecord::Base#attr_accessible+. If you set the +:accessible+ option to true, then mass assignment is allowed for this association.
+
+===== +:as+
+
+Setting the +:as+ option indicates that this is a polymorphic association. Polymorphic associations are discussed in detail later in this guide.
+
===== +:class_name+
If the name of the other model cannot be derived from the association name, you can use the +:class_name+ option to supply the model name. For example, if a supplier has an account, but the actual name of the model containing accounts is billing, you'd set things up this way:
@@ -875,10 +917,6 @@ class Supplier < ActiveRecord::Base
end
-------------------------------------------------------
-===== +:order+
-
-The +:order+ option dictates the order in which associated objects will be received (in the syntax used by a SQL +ORDER BY+ clause). Because a +has_one+ association will only retrieve a single associated object, this option should not be needed.
-
===== +:dependent+
If you set the +:dependent+ option to +:destroy+, then deleting this object will call the destroy method on the associated object to delete that object. If you set the +:dependent+ option to +:delete+, then deleting this object will delete the associated object _without_ calling its +destroy+ method. If you set the +:dependent+ option to +:nullify+, then deleting this object will set the foreign key in the association object to +NULL+.
@@ -896,10 +934,6 @@ end
TIP: In any case, Rails will not create foreign key columns for you. You need to explicitly define them as part of your migrations.
-===== +: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.
-
===== +:include+
You can use the :include option to specify second-order associations that should be eager-loaded when this association is used. For example, consider these models:
@@ -934,17 +968,21 @@ class Representative < ActiveRecord::Base
end
-------------------------------------------------------
-===== +:as+
+===== +:order+
-Setting the +:as+ option indicates that this is a polymorphic association. Polymorphic associations are discussed in detail later in this guide.
+The +:order+ option dictates the order in which associated objects will be received (in the syntax used by a SQL +ORDER BY+ clause). Because a +has_one+ association will only retrieve a single associated object, this option should not be needed.
-===== +:select+
+===== +:primary_key+
-The +:select+ option lets you override the SQL +SELECT+ clause that is used to retrieve data about the associated object. By default, Rails retrieves all columns.
+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.
-===== +:through+
+===== +:readonly+
-The +:through+ option specifies a join model through which to perform the query. +has_one :through+ associations are discussed in detail later in this guide.
+If you set the +:readonly+ option to +true+, then the associated object will be read-only when retrieved via the association.
+
+===== +:select+
+
+The +:select+ option lets you override the SQL +SELECT+ clause that is used to retrieve data about the associated object. By default, Rails retrieves all columns.
===== +:source+
@@ -954,18 +992,14 @@ The +:source+ option specifies the source association name for a +has_one :throu
The +:source_type+ option specifies the source association type for a +has_one :through+ association that proceeds through a polymorphic association.
-===== +:readonly+
+===== +:through+
-If you set the +:readonly+ option to +true+, then the associated object will be read-only when retrieved via the association.
+The +:through+ option specifies a join model through which to perform the query. +has_one :through+ associations are discussed in detail later in this guide.
===== +: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.
-===== +:accessible+
-
-The +:accessible+ option is the association version of +ActiveRecord::Base#attr_accessible+. If you set the +:accessible+ option to true, then mass assignment is allowed for this association.
-
==== When are Objects Saved?
When you assign an object to a +has_one+ association, that object is automatically saved (in order to update its foreign key). In addition, any object being replaced is also automatically saved, because its foreign key will change too.
@@ -1138,6 +1172,39 @@ class Customer < ActiveRecord::Base
end
-------------------------------------------------------
+The +has_many+ association supports these options:
+
+* +:accessible+
+* +:as+
+* +:class_name+
+* +:conditions+
+* +:counter_sql+
+* +:dependent+
+* +:extend+
+* +:finder_sql+
+* +:foreign_key+
+* +:group+
+* +:include+
+* +:limit+
+* +:offset+
+* +:order+
+* +:primary_key+
+* +:readonly+
+* +:select+
+* +:source+
+* +:source_type+
+* +:through+
+* +:uniq+
+* +:validate+
+
+===== +:accessible+
+
+The +:accessible+ option is the association version of +ActiveRecord::Base#attr_accessible+. If you set the +:accessible+ option to true, then mass assignment is allowed for this association.
+
+===== +:as+
+
+Setting the +:as+ option indicates that this is a polymorphic association, as discussed earlier in this guide.
+
===== +:class_name+
If the name of the other model cannot be derived from the association name, you can use the +:class_name+ option to supply the model name. For example, if a customer has many orders, but the actual name of the model containing orders is transactions, you'd set things up this way:
@@ -1171,16 +1238,25 @@ 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+.
-===== +:order+
+===== +:counter_sql+
-The +:order+ option dictates the order in which associated objects will be received (in the syntax used by a SQL +ORDER BY+ clause).
+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.
-[source, ruby]
--------------------------------------------------------
-class Customer < ActiveRecord::Base
- has_many :orders, :order => "date_confirmed DESC"
-end
--------------------------------------------------------
+NOTE: If you specify +:finder_sql+ but not +:counter_sql+, then the counter SQL will be generated by substituting +SELECT COUNT(*) FROM+ for the +SELECT ... FROM+ clause of your +:finder_sql+ statement.
+
+===== +:dependent+
+
+If you set the +:dependent+ option to +:destroy+, then deleting this object will call the destroy method on the associated objects to delete those objects. If you set the +:dependent+ option to +:delete_all+, then deleting this object will delete the associated objects _without_ calling their +destroy+ method. If you set the +:dependent+ option to +:nullify+, then deleting this object will set the foreign key in the associated objects to +NULL+.
+
+NOTE: This option is ignored when you use the +:through+ option on the association.
+
+===== +:extend+
+
+The +:extend+ option specifies a named module to extend the association proxy. Association extensions are discussed in detail later in this guide.
+
+===== +:finder_sql+
+
+Normally Rails automatically generates the proper SQL to fetch the association members. With the +:finder_sql+ option, you can specify a complete SQL statement to fetch them yourself. If fetching objects requires complex multi-table SQL, this may be necessary.
===== +:foreign_key+
@@ -1195,29 +1271,16 @@ end
TIP: In any case, Rails will not create foreign key columns for you. You need to explicitly define them as part of your migrations.
-===== +: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.
-
-===== +:dependent+
-
-If you set the +:dependent+ option to +:destroy+, then deleting this object will call the destroy method on the associated objects to delete those objects. If you set the +:dependent+ option to +:delete_all+, then deleting this object will delete the associated objects _without_ calling their +destroy+ method. If you set the +:dependent+ option to +:nullify+, then deleting this object will set the foreign key in the associated objects to +NULL+.
-
-NOTE: This option is ignored when you use the +:through+ option on the association.
-
-===== +:finder_sql+
-
-Normally Rails automatically generates the proper SQL to fetch the association members. With the +:finder_sql+ option, you can specify a complete SQL statement to fetch them yourself. If fetching objects requires complex multi-table SQL, this may be necessary.
-
-===== +: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.
-
-NOTE: If you specify +:finder_sql+ but not +:counter_sql+, then the counter SQL will be generated by substituting +SELECT COUNT(*) FROM+ for the +SELECT ... FROM+ clause of your +:finder_sql+ statement.
+===== +:group+
-===== +:extend+
+The +:group+ option supplies an attribute name to group the result set by, using a +GROUP BY+ clause in the finder SQL.
-The +:extend+ option specifies a named module to extend the association proxy. Association extensions are discussed in detail later in this guide.
+[source, ruby]
+-------------------------------------------------------
+class Customer < ActiveRecord::Base
+ has_many :line_items, :through => :orders, :group => "orders.id"
+end
+-------------------------------------------------------
===== +:include+
@@ -1253,31 +1316,39 @@ class LineItem < ActiveRecord::Base
end
-------------------------------------------------------
-===== +:group+
+===== +:limit+
-The +:group+ option supplies an attribute name to group the result set by, using a +GROUP BY+ clause in the finder SQL.
+The +:limit+ option lets you restrict the total number of objects that will be fetched through an association.
[source, ruby]
-------------------------------------------------------
class Customer < ActiveRecord::Base
- has_many :line_items, :through => :orders, :group => "orders.id"
+ has_many :recent_orders, :class_name => :orders, :order => "order_date DESC", :limit => 100
end
-------------------------------------------------------
-===== +:limit+
+===== +:offset+
-The +:limit+ option lets you restrict the total number of objects that will be fetched through an association.
+The +:offset+ option lets you specify the starting offset for fetching objects via an association. For example, if you set +:offset => 11+, it will skip the first 10 records.
+
+===== +:order+
+
+The +:order+ option dictates the order in which associated objects will be received (in the syntax used by a SQL +ORDER BY+ clause).
[source, ruby]
-------------------------------------------------------
class Customer < ActiveRecord::Base
- has_many :recent_orders, :class_name => :orders, :order => "order_date DESC", :limit => 100
+ has_many :orders, :order => "date_confirmed DESC"
end
-------------------------------------------------------
-===== +:offset+
+===== +:primary_key+
-The +:offset+ option lets you specify the starting offset for fetching objects via an association. For example, if you set +:offset => 11+, it will skip the first 10 records.
+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.
+
+===== +:readonly+
+
+If you set the +:readonly+ option to +true+, then the associated objects will be read-only when retrieved via the association.
===== +:select+
@@ -1285,14 +1356,6 @@ The +:select+ option lets you override the SQL +SELECT+ clause that is used to r
WARNING: If you specify your own +:select+, be sure to include the primary key and foreign key columns of the associated model. If you do not, Rails will throw an error.
-===== +:as+
-
-Setting the +:as+ option indicates that this is a polymorphic association, as discussed earlier in this guide.
-
-===== +:through+
-
-The +:through+ option specifies a join model through which to perform the query. +has_many :through+ associations provide a way to implement many-to-many relationships, as discussed earlier in this guide.
-
===== +:source+
The +:source+ option specifies the source association name for a +has_many :through+ association. You only need to use this option if the name of the source association cannot be automatically inferred from the association name.
@@ -1301,22 +1364,18 @@ The +:source+ option specifies the source association name for a +has_many :thro
The +:source_type+ option specifies the source association type for a +has_many :through+ association that proceeds through a polymorphic association.
-===== +:uniq+
+===== +:through+
-Specify the +:uniq => true+ option to remove duplicates from the collection. This is most useful in conjunction with the +:through+ option.
+The +:through+ option specifies a join model through which to perform the query. +has_many :through+ associations provide a way to implement many-to-many relationships, as discussed earlier in this guide.
-===== +:readonly+
+===== +:uniq+
-If you set the +:readonly+ option to +true+, then the associated objects will be read-only when retrieved via the association.
+Specify the +:uniq => true+ option to remove duplicates from the collection. This is most useful in conjunction with the +:through+ option.
===== +:validate+
If you set the +:validate+ option to +false+, then associated objects will not be validated whenever you save this object. By default, this is +true+: associated objects will be validated when this object is saved.
-===== +:accessible+
-
-The +:accessible+ option is the association version of +ActiveRecord::Base#attr_accessible+. If you set the +:accessible+ option to true, then mass assignment is allowed for this association.
-
==== When are Objects Saved?
When you assign an object to a +has_many+ association, that object is automatically saved (in order to update its foreign key). If you assign multiple objects in one statement, then they are all saved.
@@ -1498,24 +1557,32 @@ class Parts < ActiveRecord::Base
end
-------------------------------------------------------
-===== +:class_name+
-
-If the name of the other model cannot be derived from the association name, you can use the +:class_name+ option to supply the model name. For example, if a part has many assemblies, but the actual name of the model containing assemblies is gadgets, you'd set things up this way:
+The +has_and_belongs_to_many+ association supports these options:
+
+* +:accessible+
+* +:association_foreign_key+
+* +:class_name+
+* +:conditions+
+* +:counter_sql+
+* +:delete_sql+
+* +:extend+
+* +:finder_sql+
+* +:foreign_key+
+* +:group+
+* +:include+
+* +:insert_sql+
+* +:join_table+
+* +:limit+
+* +:offset+
+* +:order+
+* +:readonly+
+* +:select+
+* +:uniq+
+* +:validate+
-[source, ruby]
--------------------------------------------------------
-class Parts < ActiveRecord::Base
- has_and_belongs_to_many :assemblies, :class_name => :gadgets
-end
--------------------------------------------------------
-
-===== +:join_table+
-
-If the default name of the join table, based on lexical ordering, is not what you want, you can use the +:join_table+ option to override the default.
-
-===== +:foreign_key+
+===== +:accessible+
-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:
+The +:accessible+ option is the association version of +ActiveRecord::Base#attr_accessible+. If you set the +:accessible+ option to true, then mass assignment is allowed for this association.
===== +:association_foreign_key+
@@ -1531,47 +1598,38 @@ class User < ActiveRecord::Base
end
-------------------------------------------------------
-===== +:conditions+
+===== +:class_name+
-The +:conditions+ option lets you specify the conditions that the associated object must meet (in the syntax used by a SQL +WHERE+ clause).
+If the name of the other model cannot be derived from the association name, you can use the +:class_name+ option to supply the model name. For example, if a part has many assemblies, but the actual name of the model containing assemblies is gadgets, you'd set things up this way:
[source, ruby]
-------------------------------------------------------
class Parts < ActiveRecord::Base
- has_and_belongs_to_many :assemblies, :conditions => "factory = 'Seattle'"
+ has_and_belongs_to_many :assemblies, :class_name => :gadgets
end
-------------------------------------------------------
-You can also set conditions via a hash:
+===== +:conditions+
+
+The +:conditions+ option lets you specify the conditions that the associated object must meet (in the syntax used by a SQL +WHERE+ clause).
[source, ruby]
-------------------------------------------------------
class Parts < ActiveRecord::Base
- has_and_belongs_to_many :assemblies, :conditions => { :factory => 'Seattle' }
+ has_and_belongs_to_many :assemblies, :conditions => "factory = 'Seattle'"
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 +@parts.assemblies.create+ or +@parts.assemblies.build+ will create orders where the factory column has the value "Seattle".
-
-===== +:order+
-
-The +:order+ option dictates the order in which associated objects will be received (in the syntax used by a SQL +ORDER BY+ clause).
-
+You can also set conditions via a hash:
[source, ruby]
-------------------------------------------------------
class Parts < ActiveRecord::Base
- has_and_belongs_to_many :assemblies, :order => "assembly_name ASC"
+ has_and_belongs_to_many :assemblies, :conditions => { :factory => 'Seattle' }
end
-------------------------------------------------------
-===== +:uniq+
-
-Specify the +:uniq => true+ option to remove duplicates from the collection.
-
-===== +:finder_sql+
-
-Normally Rails automatically generates the proper SQL to fetch the association members. With the +:finder_sql+ option, you can specify a complete SQL statement to fetch them yourself. If fetching objects requires complex multi-table SQL, this may be necessary.
+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 +@parts.assemblies.create+ or +@parts.assemblies.build+ will create orders where the factory column has the value "Seattle".
===== +:counter_sql+
@@ -1583,17 +1641,25 @@ NOTE: If you specify +:finder_sql+ but not +:counter_sql+, then the counter SQL
Normally Rails automatically generates the proper SQL to remove links between the associated classes. With the +:delete_sql+ option, you can specify a complete SQL statement to delete them yourself.
-===== +:insert_sql+
-
-Normally Rails automatically generates the proper SQL to create links between the associated classes. With the +:insert_sql+ option, you can specify a complete SQL statement to insert them yourself.
-
===== +:extend+
The +:extend+ option specifies a named module to extend the association proxy. Association extensions are discussed in detail later in this guide.
-===== +:include+
+===== +:finder_sql+
-You can use the :include option to specify second-order associations that should be eager-loaded when this association is used.
+Normally Rails automatically generates the proper SQL to fetch the association members. With the +:finder_sql+ option, you can specify a complete SQL statement to fetch them yourself. If fetching objects requires complex multi-table SQL, this may be necessary.
+
+===== +: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:
+
+[source, ruby]
+-------------------------------------------------------
+class User < ActiveRecord::Base
+ has_and_belongs_to_many :friends, :class_name => :users,
+ :foreign_key => "this_user_id", :association_foreign_key => "other_user_id"
+end
+-------------------------------------------------------
===== +:group+
@@ -1606,6 +1672,18 @@ class Parts < ActiveRecord::Base
end
-------------------------------------------------------
+===== +:include+
+
+You can use the :include option to specify second-order associations that should be eager-loaded when this association is used.
+
+===== +:insert_sql+
+
+Normally Rails automatically generates the proper SQL to create links between the associated classes. With the +:insert_sql+ option, you can specify a complete SQL statement to insert them yourself.
+
+===== +:join_table+
+
+If the default name of the join table, based on lexical ordering, is not what you want, you can use the +:join_table+ option to override the default.
+
===== +:limit+
The +:limit+ option lets you restrict the total number of objects that will be fetched through an association.
@@ -1621,22 +1699,32 @@ end
The +:offset+ option lets you specify the starting offset for fetching objects via an association. For example, if you set +:offset => 11+, it will skip the first 10 records.
-===== +:select+
+===== +:order+
-The +:select+ option lets you override the SQL +SELECT+ clause that is used to retrieve data about the associated objects. By default, Rails retrieves all columns.
+The +:order+ option dictates the order in which associated objects will be received (in the syntax used by a SQL +ORDER BY+ clause).
+
+[source, ruby]
+-------------------------------------------------------
+class Parts < ActiveRecord::Base
+ has_and_belongs_to_many :assemblies, :order => "assembly_name ASC"
+end
+-------------------------------------------------------
===== +:readonly+
If you set the +:readonly+ option to +true+, then the associated objects will be read-only when retrieved via the association.
-===== +:validate+
+===== +:select+
-If you set the +:validate+ option to +false+, then associated objects will not be validated whenever you save this object. By default, this is +true+: associated objects will be validated when this object is saved.
+The +:select+ option lets you override the SQL +SELECT+ clause that is used to retrieve data about the associated objects. By default, Rails retrieves all columns.
-===== +:accessible+
+===== +:uniq+
-The +:accessible+ option is the association version of +ActiveRecord::Base#attr_accessible+. If you set the +:accessible+ option to true, then mass assignment is allowed for this association.
+Specify the +:uniq => true+ option to remove duplicates from the collection.
+===== +:validate+
+
+If you set the +:validate+ option to +false+, then associated objects will not be validated whenever you save this object. By default, this is +true+: associated objects will be validated when this object is saved.
==== When are Objects Saved?
@@ -1746,5 +1834,6 @@ Extensions can refer to the internals of the association proxy using these three
http://rails.lighthouseapp.com/projects/16213-rails-guides/tickets/11[Lighthouse ticket]
-* September 14, 2008: initial version by link:../authors.html#mgunderloy[Mike Gunderloy] (not yet approved for publication)
+* September 28, 2008: Corrected +has_many :through+ diagram, added polymorphic diagram, some reorganization by link:../authors.html#mgunderloy[Mike Gunderloy] . First release version.
* September 22, 2008: Added diagrams, misc. cleanup by link:../authors.html#mgunderloy[Mike Gunderloy] (not yet approved for publication)
+* September 14, 2008: initial version by link:../authors.html#mgunderloy[Mike Gunderloy] (not yet approved for publication)
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