Merge docrails changes

3 files changed, 317 insertions, 139 deletions

diff --git a/activerecord/lib/active_record/associations.rb b/activerecord/lib/active_record/associations.rb
index d916275ab9..4e33dfe69f 100755
--- a/activerecord/lib/active_record/associations.rb
+++ b/activerecord/lib/active_record/associations.rb
@@ -73,6 +73,7 @@ module ActiveRecord
     end
   end
 
+  # See ActiveRecord::Associations::ClassMethods for documentation.
   module Associations # :nodoc:
     def self.included(base)
       base.extend(ClassMethods)
@@ -150,6 +151,7 @@ module ActiveRecord
     #   #others.destroy_all               |   X   |    X     |    X
     #   #others.find(*args)               |   X   |    X     |    X
     #   #others.find_first                |   X   |          |
+    #   #others.exist?                    |   X   |    X     |    X
     #   #others.uniq                      |   X   |    X     |    X
     #   #others.reset                     |   X   |    X     |    X
     #
@@ -612,31 +614,53 @@ module ActiveRecord
     # All of the association macros can be specialized through options. This makes cases more complex than the simple and guessable ones
     # possible.
     module ClassMethods
-      # Adds the following methods for retrieval and query of collections of associated objects:
-      # +collection+ is replaced with the symbol passed as the first argument, so
-      # <tt>has_many :clients</tt> would add among others <tt>clients.empty?</tt>.
-      # * <tt>collection(force_reload = false)</tt> - Returns an array of all the associated objects.
+      # Specifies a one-to-many association. The following methods for retrieval and query of
+      # collections of associated objects will be added:
+      #
+      # [collection(force_reload = false)]
+      #   Returns an array of all the associated objects.
       #   An empty array is returned if none are found.
-      # * <tt>collection<<(object, ...)</tt> - Adds one or more objects to the collection by setting their foreign keys to the collection's primary key.
-      # * <tt>collection.delete(object, ...)</tt> - Removes one or more objects from the collection by setting their foreign keys to +NULL+.
+      # [collection<<(object, ...)]
+      #   Adds one or more objects to the collection by setting their foreign keys to the collection's primary key.
+      # [collection.delete(object, ...)]
+      #   Removes one or more objects from the collection by setting their foreign keys to +NULL+.
       #   This will also destroy the objects if they're declared as +belongs_to+ and dependent on this model.
-      # * <tt>collection=objects</tt> - Replaces the collections content by deleting and adding objects as appropriate.
-      # * <tt>collection_singular_ids</tt> - Returns an array of the associated objects' ids
-      # * <tt>collection_singular_ids=ids</tt> - Replace the collection with the objects identified by the primary keys in +ids+
-      # * <tt>collection.clear</tt> - Removes every object from the collection. This destroys the associated objects if they
-      #   are associated with <tt>:dependent => :destroy</tt>, deletes them directly from the database if <tt>:dependent => :delete_all</tt>,
-      #   otherwise sets their foreign keys to +NULL+.
-      # * <tt>collection.empty?</tt> - Returns +true+ if there are no associated objects.
-      # * <tt>collection.size</tt> - Returns the number of associated objects.
-      # * <tt>collection.find</tt> - Finds an associated object according to the same rules as Base.find.
-      # * <tt>collection.build(attributes = {}, ...)</tt> - Returns one or more new objects of the collection type that have been instantiated
-      #   with +attributes+ and linked to this object through a foreign key, but have not yet been saved. *Note:* This only works if an
-      #   associated object already exists, not if it's +nil+!
-      # * <tt>collection.create(attributes = {})</tt> - Returns a new object of the collection type that has been instantiated
-      #   with +attributes+, linked to this object through a foreign key, and that has already been saved (if it passed the validation).
-      #   *Note:* This only works if an associated object already exists, not if it's +nil+!
+      # [collection=objects]
+      #   Replaces the collections content by deleting and adding objects as appropriate.
+      # [collection_singular_ids]
+      #   Returns an array of the associated objects' ids
+      # [collection_singular_ids=ids]
+      #   Replace the collection with the objects identified by the primary keys in +ids+
+      # [collection.clear]
+      #   Removes every object from the collection. This destroys the associated objects if they
+      #   are associated with <tt>:dependent => :destroy</tt>, deletes them directly from the
+      #   database if <tt>:dependent => :delete_all</tt>, otherwise sets their foreign keys to +NULL+.
+      # [collection.empty?]
+      #   Returns +true+ if there are no associated objects.
+      # [collection.size]
+      #   Returns the number of associated objects.
+      # [collection.find(...)]
+      #   Finds an associated object according to the same rules as ActiveRecord::Base.find.
+      # [collection.exist?(...)]
+      #   Checks whether an associated object with the given conditions exists.
+      #   Uses the same rules as ActiveRecord::Base.exists?.
+      # [collection.build(attributes = {}, ...)]
+      #   Returns one or more new objects of the collection type that have been instantiated
+      #   with +attributes+ and linked to this object through a foreign key, but have not yet
+      #   been saved. <b>Note:</b> This only works if an associated object already exists, not if
+      #   it's +nil+!
+      # [collection.create(attributes = {})]
+      #   Returns a new object of the collection type that has been instantiated
+      #   with +attributes+, linked to this object through a foreign key, and that has already
+      #   been saved (if it passed the validation). <b>Note:</b> This only works if an associated
+      #   object already exists, not if it's +nil+!
+      #
+      # (*Note*: +collection+ is replaced with the symbol passed as the first argument, so
+      # <tt>has_many :clients</tt> would add among others <tt>clients.empty?</tt>.)
+      #
+      # === Example
       #
-      # Example: A Firm class declares <tt>has_many :clients</tt>, which will add:
+      # A Firm class declares <tt>has_many :clients</tt>, which will add:
       # * <tt>Firm#clients</tt> (similar to <tt>Clients.find :all, :conditions => "firm_id = #{id}"</tt>)
       # * <tt>Firm#clients<<</tt>
       # * <tt>Firm#clients.delete</tt>
@@ -647,54 +671,77 @@ module ActiveRecord
       # * <tt>Firm#clients.empty?</tt> (similar to <tt>firm.clients.size == 0</tt>)
       # * <tt>Firm#clients.size</tt> (similar to <tt>Client.count "firm_id = #{id}"</tt>)
       # * <tt>Firm#clients.find</tt> (similar to <tt>Client.find(id, :conditions => "firm_id = #{id}")</tt>)
+      # * <tt>Firm#clients.exist?(:name => 'ACME')</tt> (similar to <tt>Client.exist?(:name => 'ACME', :firm_id => firm.id)</tt>)
       # * <tt>Firm#clients.build</tt> (similar to <tt>Client.new("firm_id" => id)</tt>)
       # * <tt>Firm#clients.create</tt> (similar to <tt>c = Client.new("firm_id" => id); c.save; c</tt>)
       # The declaration can also include an options hash to specialize the behavior of the association.
       #
-      # Options are:
-      # * <tt>:class_name</tt> - Specify the class name of the association. Use it only if that name can't be inferred
+      # === Supported options
+      # [:class_name]
+      #   Specify the class name of the association. Use it only if that name can't be inferred
       #   from the association name. So <tt>has_many :products</tt> will by default be linked to the Product class, but
       #   if the real class name is SpecialProduct, you'll have to specify it with this option.
-      # * <tt>:conditions</tt> - Specify the conditions that the associated objects must meet in order to be included as a +WHERE+
+      # [:conditions]
+      #   Specify the conditions that the associated objects must meet in order to be included as a +WHERE+
       #   SQL fragment, such as <tt>price > 5 AND name LIKE 'B%'</tt>.  Record creations from the association are scoped if a hash
       #   is used.  <tt>has_many :posts, :conditions => {:published => true}</tt> will create published posts with <tt>@blog.posts.create</tt>
       #   or <tt>@blog.posts.build</tt>.
-      # * <tt>:order</tt> - Specify the order in which the associated objects are returned as an <tt>ORDER BY</tt> SQL fragment,
+      # [:order]
+      #   Specify the order in which the associated objects are returned as an <tt>ORDER BY</tt> SQL fragment,
       #   such as <tt>last_name, first_name DESC</tt>.
-      # * <tt>:foreign_key</tt> - Specify the foreign key used for the association. By default this is guessed to be the name
+      # [:foreign_key]
+      #   Specify the foreign key used for the association. By default this is guessed to be the name
       #   of this class in lower-case and "_id" suffixed. So a Person class that makes a +has_many+ association will use "person_id"
       #   as the default <tt>:foreign_key</tt>.
-      # * <tt>:primary_key</tt> - Specify the method that returns the primary key used for the association. By default this is +id+.
-      # * <tt>:dependent</tt> - If set to <tt>:destroy</tt> all the associated objects are destroyed
+      # [:primary_key]
+      #   Specify the method that returns the primary key used for the association. By default this is +id+.
+      # [:dependent]
+      #   If set to <tt>:destroy</tt> all the associated objects are destroyed
       #   alongside this object by calling their +destroy+ method.  If set to <tt>:delete_all</tt> all associated
       #   objects are deleted *without* calling their +destroy+ method.  If set to <tt>:nullify</tt> all associated
       #   objects' foreign keys are set to +NULL+ *without* calling their +save+ callbacks. *Warning:* This option is ignored when also using
       #   the <tt>:through</tt> option.
-      # * <tt>:finder_sql</tt> - Specify a complete SQL statement to fetch the association. This is a good way to go for complex
+      # [:finder_sql]
+      #   Specify a complete SQL statement to fetch the association. This is a good way to go for complex
       #   associations that depend on multiple tables. Note: When this option is used, +find_in_collection+ is _not_ added.
-      # * <tt>:counter_sql</tt> - Specify a complete SQL statement to fetch the size of the association. If <tt>:finder_sql</tt> is
+      # [:counter_sql]
+      #   Specify a complete SQL statement to fetch the size of the association. If <tt>:finder_sql</tt> is
       #   specified but not <tt>:counter_sql</tt>, <tt>:counter_sql</tt> will be generated by replacing <tt>SELECT ... FROM</tt> with <tt>SELECT COUNT(*) FROM</tt>.
-      # * <tt>:extend</tt> - Specify a named module for extending the proxy. See "Association extensions".
-      # * <tt>:include</tt> - Specify second-order associations that should be eager loaded when the collection is loaded.
-      # * <tt>:group</tt> - An attribute name by which the result should be grouped. Uses the <tt>GROUP BY</tt> SQL-clause.
-      # * <tt>:limit</tt> - An integer determining the limit on the number of rows that should be returned.
-      # * <tt>:offset</tt> - An integer determining the offset from where the rows should be fetched. So at 5, it would skip the first 4 rows.
-      # * <tt>:select</tt> - By default, this is <tt>*</tt> as in <tt>SELECT * FROM</tt>, but can be changed if you, for example, want to do a join
+      # [:extend]
+      #   Specify a named module for extending the proxy. See "Association extensions".
+      # [:include]
+      #   Specify second-order associations that should be eager loaded when the collection is loaded.
+      # [:group]
+      #   An attribute name by which the result should be grouped. Uses the <tt>GROUP BY</tt> SQL-clause.
+      # [:limit]
+      #   An integer determining the limit on the number of rows that should be returned.
+      # [:offset]
+      #   An integer determining the offset from where the rows should be fetched. So at 5, it would skip the first 4 rows.
+      # [:select]
+      #   By default, this is <tt>*</tt> as in <tt>SELECT * FROM</tt>, but can be changed if you, for example, want to do a join
       #   but not include the joined columns. Do not forget to include the primary and foreign keys, otherwise it will raise an error.
-      # * <tt>:as</tt> - Specifies a polymorphic interface (See <tt>belongs_to</tt>).
-      # * <tt>:through</tt> - Specifies a Join Model through which to perform the query.  Options for <tt>:class_name</tt> and <tt>:foreign_key</tt>
+      # [:as]
+      #   Specifies a polymorphic interface (See <tt>belongs_to</tt>).
+      # [:through]
+      #   Specifies a Join Model through which to perform the query.  Options for <tt>:class_name</tt> and <tt>:foreign_key</tt>
       #   are ignored, as the association uses the source reflection. You can only use a <tt>:through</tt> query through a <tt>belongs_to</tt>
       #   or <tt>has_many</tt> association on the join model.
-      # * <tt>:source</tt> - Specifies the source association name used by <tt>has_many :through</tt> queries.  Only use it if the name cannot be
+      # [:source]
+      #   Specifies the source association name used by <tt>has_many :through</tt> queries.  Only use it if the name cannot be
       #   inferred from the association.  <tt>has_many :subscribers, :through => :subscriptions</tt> will look for either <tt>:subscribers</tt> or
       #   <tt>:subscriber</tt> on Subscription, unless a <tt>:source</tt> is given.
-      # * <tt>:source_type</tt> - Specifies type of the source association used by <tt>has_many :through</tt> queries where the source
+      # [:source_type]
+      #   Specifies type of the source association used by <tt>has_many :through</tt> queries where the source
       #   association is a polymorphic +belongs_to+.
-      # * <tt>:uniq</tt> - If true, duplicates will be omitted from the collection. Useful in conjunction with <tt>:through</tt>.
-      # * <tt>:readonly</tt> - If true, all the associated objects are readonly through the association.
-      # * <tt>:validate</tt> - If false, don't validate the associated objects when saving the parent object. true by default.
-      # * <tt>:accessible</tt> - Mass assignment is allowed for this assocation (similar to <tt>ActiveRecord::Base#attr_accessible</tt>).
-      #
+      # [:uniq]
+      #   If true, duplicates will be omitted from the collection. Useful in conjunction with <tt>:through</tt>.
+      # [:readonly]
+      #   If true, all the associated objects are readonly through the association.
+      # [:validate]
+      #   If false, don't validate the associated objects when saving the parent object. true by default.
+      # [:accessible]
+      #   Mass assignment is allowed for this assocation (similar to <tt>ActiveRecord::Base#attr_accessible</tt>).
+
       # Option examples:
       #   has_many :comments, :order => "posted_on"
       #   has_many :comments, :include => :author
@@ -725,58 +772,91 @@ module ActiveRecord
         end
       end
 
-      # Adds the following methods for retrieval and query of a single associated object:
-      # +association+ is replaced with the symbol passed as the first argument, so
-      # <tt>has_one :manager</tt> would add among others <tt>manager.nil?</tt>.
-      # * <tt>association(force_reload = false)</tt> - Returns the associated object. +nil+ is returned if none is found.
-      # * <tt>association=(associate)</tt> - Assigns the associate object, extracts the primary key, sets it as the foreign key,
+      # Specifies a one-to-one association with another class. This method should only be used
+      # if the other class contains the foreign key. If the current class contains the foreign key,
+      # then you should use +belongs_to+ instead. See also ActiveRecord::Associations::ClassMethods's overview
+      # on when to use has_one and when to use belongs_to.
+      #
+      # The following methods for retrieval and query of a single associated object will be added:
+      #
+      # [association(force_reload = false)]
+      #   Returns the associated object. +nil+ is returned if none is found.
+      # [association=(associate)]
+      #   Assigns the associate object, extracts the primary key, sets it as the foreign key,
       #   and saves the associate object.
-      # * <tt>association.nil?</tt> - Returns +true+ if there is no associated object.
-      # * <tt>build_association(attributes = {})</tt> - Returns a new object of the associated type that has been instantiated
-      #   with +attributes+ and linked to this object through a foreign key, but has not yet been saved. Note: This ONLY works if
-      #   an association already exists. It will NOT work if the association is +nil+.
-      # * <tt>create_association(attributes = {})</tt> - Returns a new object of the associated type that has been instantiated
-      #   with +attributes+, linked to this object through a foreign key, and that has already been saved (if it passed the validation).
+      # [association.nil?]
+      #   Returns +true+ if there is no associated object.
+      # [build_association(attributes = {})]
+      #   Returns a new object of the associated type that has been instantiated
+      #   with +attributes+ and linked to this object through a foreign key, but has not
+      #   yet been saved. <b>Note:</b> This ONLY works if an association already exists.
+      #   It will NOT work if the association is +nil+.
+      # [create_association(attributes = {})]
+      #   Returns a new object of the associated type that has been instantiated
+      #   with +attributes+, linked to this object through a foreign key, and that
+      #   has already been saved (if it passed the validation).
+      #
+      # (+association+ is replaced with the symbol passed as the first argument, so
+      # <tt>has_one :manager</tt> would add among others <tt>manager.nil?</tt>.)
       #
-      # Example: An Account class declares <tt>has_one :beneficiary</tt>, which will add:
+      # === Example
+      #
+      # An Account class declares <tt>has_one :beneficiary</tt>, which will add:
       # * <tt>Account#beneficiary</tt> (similar to <tt>Beneficiary.find(:first, :conditions => "account_id = #{id}")</tt>)
       # * <tt>Account#beneficiary=(beneficiary)</tt> (similar to <tt>beneficiary.account_id = account.id; beneficiary.save</tt>)
       # * <tt>Account#beneficiary.nil?</tt>
       # * <tt>Account#build_beneficiary</tt> (similar to <tt>Beneficiary.new("account_id" => id)</tt>)
       # * <tt>Account#create_beneficiary</tt> (similar to <tt>b = Beneficiary.new("account_id" => id); b.save; b</tt>)
       #
+      # === Options
+      #
       # The declaration can also include an options hash to specialize the behavior of the association.
       #
       # Options are:
-      # * <tt>:class_name</tt> - Specify the class name of the association. Use it only if that name can't be inferred
+      # [:class_name]
+      #   Specify the class name of the association. Use it only if that name can't be inferred
       #   from the association name. So <tt>has_one :manager</tt> will by default be linked to the Manager class, but
       #   if the real class name is Person, you'll have to specify it with this option.
-      # * <tt>:conditions</tt> - Specify the conditions that the associated object must meet in order to be included as a +WHERE+
+      # [:conditions]
+      #   Specify the conditions that the associated object must meet in order to be included as a +WHERE+
       #   SQL fragment, such as <tt>rank = 5</tt>.
-      # * <tt>:order</tt> - Specify the order in which the associated objects are returned as an <tt>ORDER BY</tt> SQL fragment,
+      # [:order]
+      #   Specify the order in which the associated objects are returned as an <tt>ORDER BY</tt> SQL fragment,
       #   such as <tt>last_name, first_name DESC</tt>.
-      # * <tt>:dependent</tt> - If set to <tt>:destroy</tt>, the associated object is destroyed when this object is. If set to
+      # [:dependent]
+      #   If set to <tt>:destroy</tt>, the associated object is destroyed when this object is. If set to
       #   <tt>:delete</tt>, the associated object is deleted *without* calling its destroy method. If set to <tt>:nullify</tt>, the associated
       #   object's foreign key is set to +NULL+. Also, association is assigned.
-      # * <tt>:foreign_key</tt> - Specify the foreign key used for the association. By default this is guessed to be the name
+      # [:foreign_key]
+      #   Specify the foreign key used for the association. By default this is guessed to be the name
       #   of this class in lower-case and "_id" suffixed. So a Person class that makes a +has_one+ association will use "person_id"
       #   as the default <tt>:foreign_key</tt>.
-      # * <tt>:primary_key</tt> - Specify the method that returns the primary key used for the association. By default this is +id+.
-      # * <tt>:include</tt> - Specify second-order associations that should be eager loaded when this object is loaded.
-      # * <tt>:as</tt> - Specifies a polymorphic interface (See <tt>belongs_to</tt>).
-      # * <tt>:select</tt> - By default, this is <tt>*</tt> as in <tt>SELECT * FROM</tt>, but can be changed if, for example, you want to do a join
+      # [:primary_key]
+      #   Specify the method that returns the primary key used for the association. By default this is +id+.
+      # [:include]
+      #   Specify second-order associations that should be eager loaded when this object is loaded.
+      # [:as]
+      #   Specifies a polymorphic interface (See <tt>belongs_to</tt>).
+      # [:select]
+      #   By default, this is <tt>*</tt> as in <tt>SELECT * FROM</tt>, but can be changed if, for example, you want to do a join
       #   but not include the joined columns. Do not forget to include the primary and foreign keys, otherwise it will raise an error.
-      # * <tt>:through</tt>: Specifies a Join Model through which to perform the query.  Options for <tt>:class_name</tt> and <tt>:foreign_key</tt>
+      # [:through]
+      #   Specifies a Join Model through which to perform the query.  Options for <tt>:class_name</tt> and <tt>:foreign_key</tt>
       #   are ignored, as the association uses the source reflection. You can only use a <tt>:through</tt> query through a 
       #   <tt>has_one</tt> or <tt>belongs_to</tt> association on the join model.
-      # * <tt>:source</tt> - Specifies the source association name used by <tt>has_one :through</tt> queries.  Only use it if the name cannot be
+      # [:source]
+      #   Specifies the source association name used by <tt>has_one :through</tt> queries.  Only use it if the name cannot be
       #   inferred from the association.  <tt>has_one :favorite, :through => :favorites</tt> will look for a
       #   <tt>:favorite</tt> on Favorite, unless a <tt>:source</tt> is given.      
-      # * <tt>:source_type</tt> - Specifies type of the source association used by <tt>has_one :through</tt> queries where the source
+      # [:source_type]
+      #   Specifies type of the source association used by <tt>has_one :through</tt> queries where the source
       #   association is a polymorphic +belongs_to+.      
-      # * <tt>:readonly</tt> - If true, the associated object is readonly through the association.
-      # * <tt>:validate</tt> - If false, don't validate the associated object when saving the parent object. +false+ by default.
-      # * <tt>:accessible</tt> - Mass assignment is allowed for this assocation (similar to <tt>ActiveRecord::Base#attr_accessible</tt>).
+      # [:readonly]
+      #   If true, the associated object is readonly through the association.
+      # [:validate]
+      #   If false, don't validate the associated object when saving the parent object. +false+ by default.
+      # [:accessible]
+      #   Mass assignment is allowed for this assocation (similar to <tt>ActiveRecord::Base#attr_accessible</tt>).
       #
       # Option examples:
       #   has_one :credit_card, :dependent => :destroy  # destroys the associated credit card
@@ -816,18 +896,34 @@ module ActiveRecord
         end
       end
 
-      # Adds the following methods for retrieval and query for a single associated object for which this object holds an id:
-      # +association+ is replaced with the symbol passed as the first argument, so
-      # <tt>belongs_to :author</tt> would add among others <tt>author.nil?</tt>.
-      # * <tt>association(force_reload = false)</tt> - Returns the associated object. +nil+ is returned if none is found.
-      # * <tt>association=(associate)</tt> - Assigns the associate object, extracts the primary key, and sets it as the foreign key.
-      # * <tt>association.nil?</tt> - Returns +true+ if there is no associated object.
-      # * <tt>build_association(attributes = {})</tt> - Returns a new object of the associated type that has been instantiated
+      # Specifies a one-to-one association with another class. This method should only be used
+      # if this class contains the foreign key. If the other class contains the foreign key,
+      # then you should use +has_one+ instead. See also ActiveRecord::Associations::ClassMethods's overview
+      # on when to use +has_one+ and when to use +belongs_to+.
+      #
+      # Methods will be added for retrieval and query for a single associated object, for which
+      # this object holds an id:
+      #
+      # [association(force_reload = false)]
+      #   Returns the associated object. +nil+ is returned if none is found.
+      # [association=(associate)]
+      #   Assigns the associate object, extracts the primary key, and sets it as the foreign key.
+      # [association.nil?]
+      #   Returns +true+ if there is no associated object.
+      # [build_association(attributes = {})]
+      #   Returns a new object of the associated type that has been instantiated
       #   with +attributes+ and linked to this object through a foreign key, but has not yet been saved.
-      # * <tt>create_association(attributes = {})</tt> - Returns a new object of the associated type that has been instantiated
-      #   with +attributes+, linked to this object through a foreign key, and that has already been saved (if it passed the validation).
+      # [create_association(attributes = {})]
+      #   Returns a new object of the associated type that has been instantiated
+      #   with +attributes+, linked to this object through a foreign key, and that
+      #   has already been saved (if it passed the validation).
+      #
+      # (+association+ is replaced with the symbol passed as the first argument, so
+      # <tt>belongs_to :author</tt> would add among others <tt>author.nil?</tt>.)
       #
-      # Example: A Post class declares <tt>belongs_to :author</tt>, which will add:
+      # === Example
+      #
+      # A Post class declares <tt>belongs_to :author</tt>, which will add:
       # * <tt>Post#author</tt> (similar to <tt>Author.find(author_id)</tt>)
       # * <tt>Post#author=(author)</tt> (similar to <tt>post.author_id = author.id</tt>)
       # * <tt>Post#author?</tt> (similar to <tt>post.author == some_author</tt>)
@@ -836,23 +932,30 @@ module ActiveRecord
       # * <tt>Post#create_author</tt> (similar to <tt>post.author = Author.new; post.author.save; post.author</tt>)
       # The declaration can also include an options hash to specialize the behavior of the association.
       #
-      # Options are:
-      # * <tt>:class_name</tt> - Specify the class name of the association. Use it only if that name can't be inferred
+      # === Options
+      #
+      # [:class_name]
+      #   Specify the class name of the association. Use it only if that name can't be inferred
       #   from the association name. So <tt>has_one :author</tt> will by default be linked to the Author class, but
       #   if the real class name is Person, you'll have to specify it with this option.
-      # * <tt>:conditions</tt> - Specify the conditions that the associated object must meet in order to be included as a +WHERE+
+      # [:conditions]
+      #   Specify the conditions that the associated object must meet in order to be included as a +WHERE+
       #   SQL fragment, such as <tt>authorized = 1</tt>.
-      # * <tt>:select</tt> - By default, this is <tt>*</tt> as in <tt>SELECT * FROM</tt>, but can be changed if, for example, you want to do a join
+      # [:select]
+      #   By default, this is <tt>*</tt> as in <tt>SELECT * FROM</tt>, but can be changed if, for example, you want to do a join
       #   but not include the joined columns. Do not forget to include the primary and foreign keys, otherwise it will raise an error.
-      # * <tt>:foreign_key</tt> - Specify the foreign key used for the association. By default this is guessed to be the name
+      # [:foreign_key]
+      #   Specify the foreign key used for the association. By default this is guessed to be the name
       #   of the association with an "_id" suffix. So a class that defines a <tt>belongs_to :person</tt> association will use
       #   "person_id" as the default <tt>:foreign_key</tt>. Similarly, <tt>belongs_to :favorite_person, :class_name => "Person"</tt>
       #   will use a foreign key of "favorite_person_id".
-      # * <tt>:dependent</tt> - If set to <tt>:destroy</tt>, the associated object is destroyed when this object is. If set to
+      # [:dependent]
+      #   If set to <tt>:destroy</tt>, the associated object is destroyed when this object is. If set to
       #   <tt>:delete</tt>, the associated object is deleted *without* calling its destroy method. This option should not be specified when
       #   <tt>belongs_to</tt> is used in conjunction with a <tt>has_many</tt> relationship on another class because of the potential to leave
       #   orphaned records behind.
-      # * <tt>:counter_cache</tt> - Caches the number of belonging objects on the associate class through the use of +increment_counter+
+      # [:counter_cache]
+      #   Caches the number of belonging objects on the associate class through the use of +increment_counter+
       #   and +decrement_counter+. The counter cache is incremented when an object of this class is created and decremented when it's
       #   destroyed. This requires that a column named <tt>#{table_name}_count</tt> (such as +comments_count+ for a belonging Comment class)
       #   is used on the associate class (such as a Post class). You can also specify a custom counter cache column by providing
@@ -860,13 +963,18 @@ module ActiveRecord
       #   When creating a counter cache column, the database statement or migration must specify a default value of <tt>0</tt>, failing to do 
       #   this results in a counter with +NULL+ value, which will never increment.
       #   Note: Specifying a counter cache will add it to that model's list of readonly attributes using +attr_readonly+.
-      # * <tt>:include</tt> - Specify second-order associations that should be eager loaded when this object is loaded.
-      # * <tt>:polymorphic</tt> - Specify this association is a polymorphic association by passing +true+.
+      # [:include]
+      #   Specify second-order associations that should be eager loaded when this object is loaded.
+      # [:polymorphic]
+      #   Specify this association is a polymorphic association by passing +true+.
       #   Note: If you've enabled the counter cache, then you may want to add the counter cache attribute
       #   to the +attr_readonly+ list in the associated classes (e.g. <tt>class Post; attr_readonly :comments_count; end</tt>).
-      # * <tt>:readonly</tt> - If true, the associated object is readonly through the association.
-      # * <tt>:validate</tt> - If false, don't validate the associated objects when saving the parent object. +false+ by default.
-      # * <tt>:accessible</tt> - Mass assignment is allowed for this assocation (similar to <tt>ActiveRecord::Base#attr_accessible</tt>).
+      # [:readonly]
+      #   If true, the associated object is readonly through the association.
+      # [:validate]
+      #   If false, don't validate the associated objects when saving the parent object. +false+ by default.
+      # [:accessible]
+      #   Mass assignment is allowed for this assocation (similar to <tt>ActiveRecord::Base#attr_accessible</tt>).
       #
       # Option examples:
       #   belongs_to :firm, :foreign_key => "client_of"
@@ -952,8 +1060,9 @@ module ActiveRecord
         configure_dependency_for_belongs_to(reflection)
       end
 
-      # Associates two classes via an intermediate join table.  Unless the join table is explicitly specified as
-      # an option, it is guessed using the lexical order of the class names. So a join between Developer and Project
+      # Specifies a many-to-many relationship with another class. This associates two classes via an
+      # intermediate join table.  Unless the join table is explicitly specified as an option, it is
+      # guessed using the lexical order of the class names. So a join between Developer and Project
       # will give the default join table name of "developers_projects" because "D" outranks "P".  Note that this precedence
       # is calculated using the <tt><</tt> operator for String.  This means that if the strings are of different lengths,
       # and the strings are equal when compared up to the shortest length, then the longer string is considered of higher
@@ -968,28 +1077,48 @@ module ActiveRecord
       # associations with attributes to a real join model (see introduction).
       #
       # Adds the following methods for retrieval and query:
-      # +collection+ is replaced with the symbol passed as the first argument, so
-      # <tt>has_and_belongs_to_many :categories</tt> would add among others <tt>categories.empty?</tt>.
-      # * <tt>collection(force_reload = false)</tt> - Returns an array of all the associated objects.
+      #
+      # [collection(force_reload = false)]
+      #   Returns an array of all the associated objects.
       #   An empty array is returned if none are found.
-      # * <tt>collection<<(object, ...)</tt> - Adds one or more objects to the collection by creating associations in the join table
+      # [collection<<(object, ...)]
+      #   Adds one or more objects to the collection by creating associations in the join table
       #   (<tt>collection.push</tt> and <tt>collection.concat</tt> are aliases to this method).
-      # * <tt>collection.delete(object, ...)</tt> - Removes one or more objects from the collection by removing their associations from the join table.
+      # [collection.delete(object, ...)]
+      #   Removes one or more objects from the collection by removing their associations from the join table.
       #   This does not destroy the objects.
-      # * <tt>collection=objects</tt> - Replaces the collection's content by deleting and adding objects as appropriate.
-      # * <tt>collection_singular_ids</tt> - Returns an array of the associated objects' ids.
-      # * <tt>collection_singular_ids=ids</tt> - Replace the collection by the objects identified by the primary keys in +ids+.
-      # * <tt>collection.clear</tt> - Removes every object from the collection. This does not destroy the objects.
-      # * <tt>collection.empty?</tt> - Returns +true+ if there are no associated objects.
-      # * <tt>collection.size</tt> - Returns the number of associated objects.
-      # * <tt>collection.find(id)</tt> - Finds an associated object responding to the +id+ and that
+      # [collection=objects]
+      #   Replaces the collection's content by deleting and adding objects as appropriate.
+      # [collection_singular_ids]
+      #   Returns an array of the associated objects' ids.
+      # [collection_singular_ids=ids]
+      #   Replace the collection by the objects identified by the primary keys in +ids+.
+      # [collection.clear]
+      #   Removes every object from the collection. This does not destroy the objects.
+      # [collection.empty?]
+      #   Returns +true+ if there are no associated objects.
+      # [collection.size]
+      #   Returns the number of associated objects.
+      # [collection.find(id)]
+      #   Finds an associated object responding to the +id+ and that
       #   meets the condition that it has to be associated with this object.
-      # * <tt>collection.build(attributes = {})</tt> - Returns a new object of the collection type that has been instantiated
+      #   Uses the same rules as ActiveRecord::Base.find.
+      # [collection.exist?(...)]
+      #   Checks whether an associated object with the given conditions exists.
+      #   Uses the same rules as ActiveRecord::Base.exists?.
+      # [collection.build(attributes = {})]
+      #   Returns a new object of the collection type that has been instantiated
       #   with +attributes+ and linked to this object through the join table, but has not yet been saved.
-      # * <tt>collection.create(attributes = {})</tt> - Returns a new object of the collection type that has been instantiated
+      # [collection.create(attributes = {})]
+      #   Returns a new object of the collection type that has been instantiated
       #   with +attributes+, linked to this object through the join table, and that has already been saved (if it passed the validation).
       #
-      # Example: A Developer class declares <tt>has_and_belongs_to_many :projects</tt>, which will add:
+      # (+collection+ is replaced with the symbol passed as the first argument, so
+      # <tt>has_and_belongs_to_many :categories</tt> would add among others <tt>categories.empty?</tt>.)
+      #
+      # === Example
+      #
+      # A Developer class declares <tt>has_and_belongs_to_many :projects</tt>, which will add:
       # * <tt>Developer#projects</tt>
       # * <tt>Developer#projects<<</tt>
       # * <tt>Developer#projects.delete</tt>
@@ -1000,45 +1129,66 @@ module ActiveRecord
       # * <tt>Developer#projects.empty?</tt>
       # * <tt>Developer#projects.size</tt>
       # * <tt>Developer#projects.find(id)</tt>
+      # * <tt>Developer#clients.exist?(...)</tt>
       # * <tt>Developer#projects.build</tt> (similar to <tt>Project.new("project_id" => id)</tt>)
       # * <tt>Developer#projects.create</tt> (similar to <tt>c = Project.new("project_id" => id); c.save; c</tt>)
       # The declaration may include an options hash to specialize the behavior of the association.
       #
-      # Options are:
-      # * <tt>:class_name</tt> - Specify the class name of the association. Use it only if that name can't be inferred
+      # === Options
+      #
+      # [:class_name]
+      #   Specify the class name of the association. Use it only if that name can't be inferred
       #   from the association name. So <tt>has_and_belongs_to_many :projects</tt> will by default be linked to the
       #   Project class, but if the real class name is SuperProject, you'll have to specify it with this option.
-      # * <tt>:join_table</tt> - Specify the name of the join table if the default based on lexical order isn't what you want.
-      #   WARNING: If you're overwriting the table name of either class, the +table_name+ method MUST be declared underneath any
-      #   +has_and_belongs_to_many+ declaration in order to work.
-      # * <tt>:foreign_key</tt> - Specify the foreign key used for the association. By default this is guessed to be the name
+      # [:join_table]
+      #   Specify the name of the join table if the default based on lexical order isn't what you want.
+      #   <b>WARNING:</b> If you're overwriting the table name of either class, the +table_name+ method
+      #   MUST be declared underneath any +has_and_belongs_to_many+ declaration in order to work.
+      # [:foreign_key]
+      #   Specify the foreign key used for the association. By default this is guessed to be the name
       #   of this class in lower-case and "_id" suffixed. So a Person class that makes a +has_and_belongs_to_many+ association
       #   will use "person_id" as the default <tt>:foreign_key</tt>.
-      # * <tt>:association_foreign_key</tt> - Specify the association foreign key used for the association. By default this is
+      # [:association_foreign_key]
+      #   Specify the association foreign key used for the association. By default this is
       #   guessed to be the name of the associated class in lower-case and "_id" suffixed. So if the associated class is Project,
       #   the +has_and_belongs_to_many+ association will use "project_id" as the default <tt>:association_foreign_key</tt>.
-      # * <tt>:conditions</tt> - Specify the conditions that the associated object must meet in order to be included as a +WHERE+
+      # [:conditions]
+      #   Specify the conditions that the associated object must meet in order to be included as a +WHERE+
       #   SQL fragment, such as <tt>authorized = 1</tt>.  Record creations from the association are scoped if a hash is used.  
       #   <tt>has_many :posts, :conditions => {:published => true}</tt> will create published posts with <tt>@blog.posts.create</tt> 
       #   or <tt>@blog.posts.build</tt>.
-      # * <tt>:order</tt> - Specify the order in which the associated objects are returned as an <tt>ORDER BY</tt> SQL fragment,
+      # [:order]
+      #   Specify the order in which the associated objects are returned as an <tt>ORDER BY</tt> SQL fragment,
       #   such as <tt>last_name, first_name DESC</tt>
-      # * <tt>:uniq</tt> - If true, duplicate associated objects will be ignored by accessors and query methods.
-      # * <tt>:finder_sql</tt> - Overwrite the default generated SQL statement used to fetch the association with a manual statement
-      # * <tt>:delete_sql</tt> - Overwrite the default generated SQL statement used to remove links between the associated
+      # [:uniq]
+      #   If true, duplicate associated objects will be ignored by accessors and query methods.
+      # [:finder_sql]
+      #   Overwrite the default generated SQL statement used to fetch the association with a manual statement
+      # [:delete_sql]
+      #   Overwrite the default generated SQL statement used to remove links between the associated
       #   classes with a manual statement.
-      # * <tt>:insert_sql</tt> - Overwrite the default generated SQL statement used to add links between the associated classes
+      # [:insert_sql]
+      #   Overwrite the default generated SQL statement used to add links between the associated classes
       #   with a manual statement.
-      # * <tt>:extend</tt> - Anonymous module for extending the proxy, see "Association extensions".
-      # * <tt>:include</tt> - Specify second-order associations that should be eager loaded when the collection is loaded.
-      # * <tt>:group</tt> - An attribute name by which the result should be grouped. Uses the <tt>GROUP BY</tt> SQL-clause.
-      # * <tt>:limit</tt> - An integer determining the limit on the number of rows that should be returned.
-      # * <tt>:offset</tt> - An integer determining the offset from where the rows should be fetched. So at 5, it would skip the first 4 rows.
-      # * <tt>:select</tt> - By default, this is <tt>*</tt> as in <tt>SELECT * FROM</tt>, but can be changed if, for example, you want to do a join
+      # [:extend]
+      #   Anonymous module for extending the proxy, see "Association extensions".
+      # [:include]
+      #   Specify second-order associations that should be eager loaded when the collection is loaded.
+      # [:group]
+      #   An attribute name by which the result should be grouped. Uses the <tt>GROUP BY</tt> SQL-clause.
+      # [:limit]
+      #   An integer determining the limit on the number of rows that should be returned.
+      # [:offset]
+      #   An integer determining the offset from where the rows should be fetched. So at 5, it would skip the first 4 rows.
+      # [:select]
+      #   By default, this is <tt>*</tt> as in <tt>SELECT * FROM</tt>, but can be changed if, for example, you want to do a join
       #   but not include the joined columns. Do not forget to include the primary and foreign keys, otherwise it will raise an error.
-      # * <tt>:readonly</tt> - If true, all the associated objects are readonly through the association.
-      # * <tt>:validate</tt> - If false, don't validate the associated objects when saving the parent object. +true+ by default.
-      # * <tt>:accessible</tt> - Mass assignment is allowed for this assocation (similar to <tt>ActiveRecord::Base#attr_accessible</tt>).
+      # [:readonly]
+      #   If true, all the associated objects are readonly through the association.
+      # [:validate]
+      #   If false, don't validate the associated objects when saving the parent object. +true+ by default.
+      # [:accessible<]
+      #   Mass assignment is allowed for this assocation (similar to <tt>ActiveRecord::Base#attr_accessible</tt>).
       #
       # Option examples:
       #   has_and_belongs_to_many :projects
diff --git a/activerecord/lib/active_record/base.rb b/activerecord/lib/active_record/base.rb
index 4f5d72a0be..9cb64223e2 100755
--- a/activerecord/lib/active_record/base.rb
+++ b/activerecord/lib/active_record/base.rb
@@ -83,8 +83,33 @@ module ActiveRecord #:nodoc:
   class ReadOnlyRecord < ActiveRecordError
   end
 
-  # Used by Active Record transaction mechanism to distinguish rollback from other exceptional situations.
-  # You can use it to roll your transaction back explicitly in the block passed to +transaction+ method.
+  # ActiveRecord::Transactions::ClassMethods.transaction uses this exception
+  # to distinguish a deliberate rollback from other exceptional situations.
+  # Normally, raising an exception will cause the +transaction+ method to rollback
+  # the database transaction *and* pass on the exception. But if you raise an
+  # ActiveRecord::Rollback exception, then the database transaction will be rolled back,
+  # without passing on the exception.
+  #
+  # For example, you could do this in your controller to rollback a transaction:
+  #
+  #   class BooksController < ActionController::Base
+  #     def create
+  #       Book.transaction do
+  #         book = Book.new(params[:book])
+  #         book.save!
+  #         if today_is_friday?
+  #           # The system must fail on Friday so that our support department
+  #           # won't be out of job. We silently rollback this transaction
+  #           # without telling the user.
+  #           raise ActiveRecord::Rollback, "Call tech support!"
+  #         end
+  #       end
+  #       # ActiveRecord::Rollback is the only exception that won't be passed on
+  #       # by ActiveRecord::Base.transaction, so this line will still be reached
+  #       # even on Friday.
+  #       redirect_to root_url
+  #     end
+  #   end
   class Rollback < ActiveRecordError
   end
 
diff --git a/activerecord/lib/active_record/transactions.rb b/activerecord/lib/active_record/transactions.rb
index 354a6c83a2..0531afbb52 100644
--- a/activerecord/lib/active_record/transactions.rb
+++ b/activerecord/lib/active_record/transactions.rb
@@ -66,12 +66,15 @@ module ActiveRecord
     # will happen under the protected cover of a transaction. So you can use validations to check for values that the transaction
     # depends on or you can raise exceptions in the callbacks to rollback.
     #
-    # == Exception handling
+    # == Exception handling and rolling back
     #
     # Also have in mind that exceptions thrown within a transaction block will be propagated (after triggering the ROLLBACK), so you
-    # should be ready to catch those in your application code. One exception is the ActiveRecord::Rollback exception, which will
-    # trigger a ROLLBACK when raised, but not be re-raised by the transaction block.
+    # should be ready to catch those in your application code.
+    #
+    # One exception is the ActiveRecord::Rollback exception, which will trigger a ROLLBACK when raised,
+    # but not be re-raised by the transaction block.
     module ClassMethods
+      # See ActiveRecord::Transactions::ClassMethods for detailed documentation.
       def transaction(&block)
         connection.increment_open_transactions