Add has_one :through support, finally. Closes #4756 [thechrisoshow]

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@9067 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

3 files changed, 98 insertions, 20 deletions

diff --git a/activerecord/lib/active_record/association_preload.rb b/activerecord/lib/active_record/association_preload.rb
index cc657dc433..0c31c85bb0 100644
--- a/activerecord/lib/active_record/association_preload.rb
+++ b/activerecord/lib/active_record/association_preload.rb
@@ -48,6 +48,14 @@ module ActiveRecord
           association_proxy.target.push(*[associated_record].flatten)
         end
       end
+      
+      def add_preloaded_record_to_collection(parent_records, reflection_name, associated_record)
+        parent_records.each do |parent_record|
+          association_proxy = parent_record.send(reflection_name)
+          association_proxy.loaded
+          association_proxy.target = associated_record
+        end
+      end
 
       def set_association_collection_records(id_to_record_map, reflection_name, associated_records, key)
         associated_records.each do |associated_record|
@@ -97,11 +105,27 @@ module ActiveRecord
       end
 
       def preload_has_one_association(records, reflection, preload_options={})
-        id_to_record_map, ids = construct_id_map(records)
-        records.each {|record| record.send("set_#{reflection.name}_target", nil)}
+        id_to_record_map, ids = construct_id_map(records)        
+        options = reflection.options
+        if options[:through]
+          records.each {|record| record.send(reflection.name) && record.send(reflection.name).loaded}
+          through_records = preload_through_records(records, reflection, options[:through])
+          through_reflection = reflections[options[:through]]
+          through_primary_key = through_reflection.primary_key_name
+          unless through_records.empty?
+            source = reflection.source_reflection.name
+            through_records.first.class.preload_associations(through_records, source)
+            through_records.compact.each do |through_record|
+              add_preloaded_record_to_collection(id_to_record_map[through_record[through_primary_key].to_i],
+                                                 reflection.name, through_record.send(source))
+            end
+          end          
+        else          
+          records.each {|record| record.send("set_#{reflection.name}_target", nil)}
 
-        set_association_single_records(id_to_record_map, reflection.name, find_associated_records(ids, reflection, preload_options),
-                                       reflection.primary_key_name)
+
+          set_association_single_records(id_to_record_map, reflection.name, find_associated_records(ids, reflection, preload_options), reflection.primary_key_name)
+        end                                       
       end
 
       def preload_has_many_association(records, reflection, preload_options={})
@@ -126,7 +150,7 @@ module ActiveRecord
                                              reflection.primary_key_name)
         end
       end
-
+      
       def preload_through_records(records, reflection, through_association)
         through_reflection = reflections[through_association]
         through_primary_key = through_reflection.primary_key_name
diff --git a/activerecord/lib/active_record/associations.rb b/activerecord/lib/active_record/associations.rb
index d7d5d9b312..0e07ee4913 100755
--- a/activerecord/lib/active_record/associations.rb
+++ b/activerecord/lib/active_record/associations.rb
@@ -6,6 +6,7 @@ require 'active_record/associations/has_one_association'
 require 'active_record/associations/has_many_association'
 require 'active_record/associations/has_many_through_association'
 require 'active_record/associations/has_and_belongs_to_many_association'
+require 'active_record/associations/has_one_through_association'
 
 module ActiveRecord
   class HasManyThroughAssociationNotFoundError < ActiveRecordError #:nodoc:
@@ -737,6 +738,12 @@ module ActiveRecord
       #   as the default +foreign_key+.
       # * <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>:through</tt>: 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
+      #   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>:readonly</tt> - if set to +true+, the associated object is readonly through the association.
       #
       # Option examples:
@@ -746,27 +753,34 @@ module ActiveRecord
       #   has_one :project_manager, :class_name => "Person", :conditions => "role = 'project_manager'"
       #   has_one :attachment, :as => :attachable
       #   has_one :boss, :readonly => :true
+      #   has_one :club, :through => :membership
+      #   has_one :primary_address, :through => :addressables, :conditions => ["addressable.primary = ?", true], :source => :addressable
       def has_one(association_id, options = {})
-        reflection = create_has_one_reflection(association_id, options)
+        if options[:through]
+          reflection = create_has_one_through_reflection(association_id, options)
+          association_accessor_methods(reflection, ActiveRecord::Associations::HasOneThroughAssociation)
+        else
+          reflection = create_has_one_reflection(association_id, options)
 
-        ivar = "@#{reflection.name}"
+          ivar = "@#{reflection.name}"
 
-        method_name = "has_one_after_save_for_#{reflection.name}".to_sym
-        define_method(method_name) do
-          association = instance_variable_get("#{ivar}") if instance_variable_defined?("#{ivar}")
+          method_name = "has_one_after_save_for_#{reflection.name}".to_sym
+          define_method(method_name) do
+            association = instance_variable_get("#{ivar}") if instance_variable_defined?("#{ivar}")
 
-          if !association.nil? && (new_record? || association.new_record? || association["#{reflection.primary_key_name}"] != id)
-            association["#{reflection.primary_key_name}"] = id
-            association.save(true)
+            if !association.nil? && (new_record? || association.new_record? || association["#{reflection.primary_key_name}"] != id)
+              association["#{reflection.primary_key_name}"] = id
+              association.save(true)
+            end
           end
-        end
-        after_save method_name
+          after_save method_name
 
-        association_accessor_methods(reflection, HasOneAssociation)
-        association_constructor_method(:build,  reflection, HasOneAssociation)
-        association_constructor_method(:create, reflection, HasOneAssociation)
+          association_accessor_methods(reflection, HasOneAssociation)
+          association_constructor_method(:build,  reflection, HasOneAssociation)
+          association_constructor_method(:create, reflection, HasOneAssociation)
 
-        configure_dependency_for_has_one(reflection)
+          configure_dependency_for_has_one(reflection)
+        end
       end
 
       # Adds the following methods for retrieval and query for a single associated object for which this object holds an id:
@@ -1058,7 +1072,12 @@ module ActiveRecord
               association = association_proxy_class.new(self, reflection)
             end
 
-            association.replace(new_value)
+            if association_proxy_class == HasOneThroughAssociation
+              association.create_through_record(new_value)
+              self.send(reflection.name, new_value)
+            else
+              association.replace(new_value)              
+            end
 
             instance_variable_set(ivar, new_value.nil? ? nil : association)
           end
@@ -1300,6 +1319,13 @@ module ActiveRecord
 
           create_reflection(:has_one, association_id, options, self)
         end
+        
+        def create_has_one_through_reflection(association_id, options)
+          options.assert_valid_keys(
+            :class_name, :foreign_key, :remote, :conditions, :order, :include, :dependent, :counter_cache, :extend, :as, :through, :source
+          )
+          create_reflection(:has_one, association_id, options, self)
+        end
 
         def create_belongs_to_reflection(association_id, options)
           options.assert_valid_keys(
diff --git a/activerecord/lib/active_record/associations/has_one_through_association.rb b/activerecord/lib/active_record/associations/has_one_through_association.rb
new file mode 100644
index 0000000000..ecf9d8208d
--- /dev/null
+++ b/activerecord/lib/active_record/associations/has_one_through_association.rb
@@ -0,0 +1,28 @@
+module ActiveRecord
+  module Associations
+    class HasOneThroughAssociation < ActiveRecord::Associations::HasManyThroughAssociation
+      
+      def create_through_record(new_value) #nodoc:
+        klass = @reflection.through_reflection.klass
+
+        current_object = @owner.send(@reflection.through_reflection.name)
+        
+        if current_object
+          klass.destroy(current_object)
+          @owner.clear_association_cache
+        end
+        
+        @owner.send(@reflection.through_reflection.name,  klass.send(:create, construct_join_attributes(new_value)))
+      end
+      
+    private
+      def find(*args)
+        super(args.merge(:limit => 1))
+      end
+    
+      def find_target
+        super.first
+      end        
+    end        
+  end
+end