Fix the has_and_belongs_to_many #create doesn't populate the join for new records. Closes #3692 [josh@hasmanythrough.com]

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@4379 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

2 files changed, 17 insertions, 0 deletions

diff --git a/activerecord/lib/active_record/associations.rb b/activerecord/lib/active_record/associations.rb
index e1a0289039..ff10763cbf 100755
--- a/activerecord/lib/active_record/associations.rb
+++ b/activerecord/lib/active_record/associations.rb
@@ -763,6 +763,10 @@ module ActiveRecord
       # * <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
       #   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
+      #   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
+      #   with +attributes+ and linked to this object through the join table and that has already been saved (if it passed the validation).
       #
       # Example: An Developer class declares <tt>has_and_belongs_to_many :projects</tt>, which will add:
       # * <tt>Developer#projects</tt>
@@ -775,6 +779,8 @@ module ActiveRecord
       # * <tt>Developer#projects.empty?</tt>
       # * <tt>Developer#projects.size</tt>
       # * <tt>Developer#projects.find(id)</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:
diff --git a/activerecord/lib/active_record/associations/has_and_belongs_to_many_association.rb b/activerecord/lib/active_record/associations/has_and_belongs_to_many_association.rb
index cc6549f3ae..42cf549dcb 100644
--- a/activerecord/lib/active_record/associations/has_and_belongs_to_many_association.rb
+++ b/activerecord/lib/active_record/associations/has_and_belongs_to_many_association.rb
@@ -13,6 +13,17 @@ module ActiveRecord
         record
       end
 
+      def create(attributes = {})
+        # Can't use Base.create since the foreign key may be a protected attribute.
+        if attributes.is_a?(Array)
+          attributes.collect { |attr| create(attr) }
+        else
+          record = build(attributes)
+          insert_record(record) unless @owner.new_record?
+          record
+        end
+      end
+
       def find_first
         load_target.first
       end