Make scopes use relations under the hood

11 files changed, 329 insertions, 269 deletions

diff --git a/activerecord/lib/active_record/associations.rb b/activerecord/lib/active_record/associations.rb
index 50fd4aafec..d6ecd0a5e3 100755
--- a/activerecord/lib/active_record/associations.rb
+++ b/activerecord/lib/active_record/associations.rb
@@ -1703,24 +1703,30 @@ module ActiveRecord
         end
 
         def construct_finder_arel_with_included_associations(options, join_dependency)
-          scope = scope(:find)
-
           relation = active_relation
 
           for association in join_dependency.join_associations
             relation = association.join_relation(relation)
           end
 
-          relation = relation.joins(construct_join(options[:joins], scope)).
+          relation = relation.joins(options[:joins]).
             select(column_aliases(join_dependency)).
-            group(options[:group] || (scope && scope[:group])).
-            having(options[:having] || (scope && scope[:having])).
-            order(construct_order(options[:order], scope)).
-            where(construct_conditions(options[:conditions], scope)).
-            from((scope && scope[:from]) || options[:from])
+            group(options[:group]).
+            having(options[:having]).
+            order(options[:order]).
+            where(options[:conditions]).
+            from(options[:from])
+
+          scoped_relation = current_scoped_methods
+          scoped_relation_limit = scoped_relation.taken if scoped_relation
+
+          relation = current_scoped_methods.except(:limit).merge(relation) if current_scoped_methods
 
-          relation = relation.where(construct_arel_limited_ids_condition(options, join_dependency)) if !using_limitable_reflections?(join_dependency.reflections) && ((scope && scope[:limit]) || options[:limit])
-          relation = relation.limit(construct_limit(options[:limit], scope)) if using_limitable_reflections?(join_dependency.reflections)
+          if !using_limitable_reflections?(join_dependency.reflections) && ((scoped_relation && scoped_relation.taken) || options[:limit])
+            relation = relation.where(construct_arel_limited_ids_condition(options, join_dependency))
+          end
+
+          relation = relation.limit(options[:limit] || scoped_relation_limit) if using_limitable_reflections?(join_dependency.reflections)
 
           relation
         end
@@ -1748,23 +1754,23 @@ module ActiveRecord
         end
 
         def construct_finder_sql_for_association_limiting(options, join_dependency)
-          scope = scope(:find)
-
           relation = active_relation
 
           for association in join_dependency.join_associations
             relation = association.join_relation(relation)
           end
 
-          relation = relation.joins(construct_join(options[:joins], scope)).
-            where(construct_conditions(options[:conditions], scope)).
-            group(options[:group] || (scope && scope[:group])).
-            having(options[:having] || (scope && scope[:having])).
-            order(construct_order(options[:order], scope)).
-            limit(construct_limit(options[:limit], scope)).
-            offset(construct_limit(options[:offset], scope)).
-            from(options[:from]).
-            select(connection.distinct("#{connection.quote_table_name table_name}.#{primary_key}", construct_order(options[:order], scope(:find)).join(",")))
+          relation = relation.joins(options[:joins]).
+            where(options[:conditions]).
+            group(options[:group]).
+            having(options[:having]).
+            order(options[:order]).
+            limit(options[:limit]).
+            offset(options[:offset]).
+            from(options[:from])
+
+          relation = current_scoped_methods.except(:select, :includes, :eager_load).merge(relation) if current_scoped_methods
+          relation = relation.select(connection.distinct("#{connection.quote_table_name table_name}.#{primary_key}", options[:order]))
 
           relation.to_sql
         end
@@ -2030,118 +2036,85 @@ module ActiveRecord
 
             def association_join
               return @join if @join
-              connection = reflection.active_record.connection
+
+              aliased_table = Arel::Table.new(table_name, :as => @aliased_table_name, :engine => active_relation_engine)
+              parent_table = Arel::Table.new(parent.table_name, :as => parent.aliased_table_name, :engine => active_relation_engine)
+
               @join = case reflection.macro
-                when :has_and_belongs_to_many
-                  ["%s.%s = %s.%s " % [
-                     connection.quote_table_name(aliased_join_table_name),
-                     options[:foreign_key] || reflection.active_record.to_s.foreign_key,
-                     connection.quote_table_name(parent.aliased_table_name),
-                     reflection.active_record.primary_key],
-                  "%s.%s = %s.%s " % [
-                     connection.quote_table_name(aliased_table_name),
-                     klass.primary_key,
-                     connection.quote_table_name(aliased_join_table_name),
-                     options[:association_foreign_key] || klass.to_s.foreign_key
-                     ]
-                  ]
-                when :has_many, :has_one
-                  if reflection.options[:through]
-                    jt_foreign_key = jt_as_extra = jt_source_extra = jt_sti_extra = nil
-                    first_key = second_key = as_extra = nil
-
-                    if through_reflection.options[:as] # has_many :through against a polymorphic join
-                      jt_foreign_key = through_reflection.options[:as].to_s + '_id'
-                      jt_as_extra = " AND %s.%s = %s" % [
-                        connection.quote_table_name(aliased_join_table_name),
-                        connection.quote_column_name(through_reflection.options[:as].to_s + '_type'),
-                        klass.quote_value(parent.active_record.base_class.name)
-                      ]
+              when :has_and_belongs_to_many
+                join_table = Arel::Table.new(options[:join_table], :as => aliased_join_table_name, :engine => active_relation_engine)
+                fk = options[:foreign_key] || reflection.active_record.to_s.foreign_key
+                klass_fk = options[:association_foreign_key] || klass.to_s.foreign_key
+
+                [
+                  join_table[fk].eq(parent_table[reflection.active_record.primary_key]),
+                  aliased_table[klass.primary_key].eq(join_table[klass_fk])
+                ]
+              when :has_many, :has_one
+                if reflection.options[:through]
+                  join_table = Arel::Table.new(through_reflection.klass.table_name, :as => aliased_join_table_name, :engine => active_relation_engine)
+                  jt_foreign_key = jt_as_extra = jt_source_extra = jt_sti_extra = nil
+                  first_key = second_key = as_extra = nil
+
+                  if through_reflection.options[:as] # has_many :through against a polymorphic join
+                    jt_foreign_key = through_reflection.options[:as].to_s + '_id'
+                    jt_as_extra = join_table[through_reflection.options[:as].to_s + '_type'].eq(parent.active_record.base_class.name)
+                  else
+                    jt_foreign_key = through_reflection.primary_key_name
+                  end
+
+                  case source_reflection.macro
+                  when :has_many
+                    if source_reflection.options[:as]
+                      first_key   = "#{source_reflection.options[:as]}_id"
+                      second_key  = options[:foreign_key] || primary_key
+                      as_extra    = aliased_table["#{source_reflection.options[:as]}_type"].eq(source_reflection.active_record.base_class.name)
                     else
-                      jt_foreign_key = through_reflection.primary_key_name
+                      first_key   = through_reflection.klass.base_class.to_s.foreign_key
+                      second_key  = options[:foreign_key] || primary_key
                     end
 
-                    case source_reflection.macro
-                      when :has_many
-                        if source_reflection.options[:as]
-                          first_key   = "#{source_reflection.options[:as]}_id"
-                          second_key  = options[:foreign_key] || primary_key
-                          as_extra    = " AND %s.%s = %s" % [
-                            connection.quote_table_name(aliased_table_name),
-                            connection.quote_column_name("#{source_reflection.options[:as]}_type"),
-                            klass.quote_value(source_reflection.active_record.base_class.name)
-                          ]
-                        else
-                          first_key   = through_reflection.klass.base_class.to_s.foreign_key
-                          second_key  = options[:foreign_key] || primary_key
-                        end
-
-                        unless through_reflection.klass.descends_from_active_record?
-                          jt_sti_extra = " AND %s.%s = %s" % [
-                            connection.quote_table_name(aliased_join_table_name),
-                            connection.quote_column_name(through_reflection.active_record.inheritance_column),
-                            through_reflection.klass.quote_value(through_reflection.klass.sti_name)]
-                        end
-                      when :belongs_to
-                        first_key = primary_key
-                        if reflection.options[:source_type]
-                          second_key = source_reflection.association_foreign_key
-                          jt_source_extra = " AND %s.%s = %s" % [
-                            connection.quote_table_name(aliased_join_table_name),
-                            connection.quote_column_name(reflection.source_reflection.options[:foreign_type]),
-                            klass.quote_value(reflection.options[:source_type])
-                          ]
-                        else
-                          second_key = source_reflection.primary_key_name
-                        end
+                    unless through_reflection.klass.descends_from_active_record?
+                      jt_sti_extra = join_table[through_reflection.active_record.inheritance_column].eq(through_reflection.klass.sti_name)
+                    end
+                  when :belongs_to
+                    first_key = primary_key
+                    if reflection.options[:source_type]
+                      second_key = source_reflection.association_foreign_key
+                      jt_source_extra = join_table[reflection.source_reflection.options[:foreign_type]].eq(reflection.options[:source_type])
+                    else
+                      second_key = source_reflection.primary_key_name
                     end
-
-                    ["(%s.%s = %s.%s%s%s%s) " % [
-                      connection.quote_table_name(parent.aliased_table_name),
-                      connection.quote_column_name(parent.primary_key),
-                      connection.quote_table_name(aliased_join_table_name),
-                      connection.quote_column_name(jt_foreign_key),
-                      jt_as_extra, jt_source_extra, jt_sti_extra],
-                    "(%s.%s = %s.%s%s) " % [
-                      connection.quote_table_name(aliased_table_name),
-                      connection.quote_column_name(first_key),
-                      connection.quote_table_name(aliased_join_table_name),
-                      connection.quote_column_name(second_key),
-                      as_extra]
-                    ]
-
-                 elsif reflection.options[:as]
-                    "%s.%s = %s.%s AND %s.%s = %s" % [
-                      connection.quote_table_name(aliased_table_name),
-                      "#{reflection.options[:as]}_id",
-                      connection.quote_table_name(parent.aliased_table_name),
-                      parent.primary_key,
-                      connection.quote_table_name(aliased_table_name),
-                      "#{reflection.options[:as]}_type",
-                      klass.quote_value(parent.active_record.base_class.name)
-                    ]
-                 else
-                    foreign_key = options[:foreign_key] || reflection.active_record.name.foreign_key
-                    "%s.%s = %s.%s " % [
-                      aliased_table_name,
-                      foreign_key,
-                      parent.aliased_table_name,
-                      reflection.options[:primary_key] || parent.primary_key
-                    ]
                   end
-                when :belongs_to
-                  "%s.%s = %s.%s " % [
-                   connection.quote_table_name(aliased_table_name),
-                   reflection.klass.primary_key,
-                   connection.quote_table_name(parent.aliased_table_name),
-                   options[:foreign_key] || reflection.primary_key_name
+
+                  [
+                    [parent_table[parent.primary_key].eq(join_table[jt_foreign_key]), jt_as_extra, jt_source_extra, jt_sti_extra].reject{|x| x.blank? },
+                    aliased_table[first_key].eq(join_table[second_key])
                   ]
+                elsif reflection.options[:as]
+                  id_rel = aliased_table["#{reflection.options[:as]}_id"].eq(parent_table[parent.primary_key])
+                  type_rel = aliased_table["#{reflection.options[:as]}_type"].eq(parent.active_record.base_class.name)
+                  [id_rel, type_rel]
+                else
+                  foreign_key = options[:foreign_key] || reflection.active_record.name.foreign_key
+                  [aliased_table[foreign_key].eq(parent_table[reflection.options[:primary_key] || parent.primary_key])]
+                end
+              when :belongs_to
+                [aliased_table[reflection.klass.primary_key].eq(parent_table[options[:foreign_key] || reflection.primary_key_name])]
+              end
+
+              unless klass.descends_from_active_record?
+                sti_column = aliased_table[klass.inheritance_column]
+                sti_condition = sti_column.eq(klass.sti_name)
+                klass.send(:subclasses).each {|subclass| sti_condition = sti_condition.or(sti_column.eq(subclass.sti_name)) }
+
+                @join << sti_condition
               end
-              @join << %(AND %s) % [
-                klass.send(:type_condition, aliased_table_name)] unless klass.descends_from_active_record?
 
               [through_reflection, reflection].each do |ref|
-                @join << "AND #{interpolate_sql(sanitize_sql(ref.options[:conditions], aliased_table_name))} " if ref && ref.options[:conditions]
+                if ref && ref.options[:conditions]
+                  @join << interpolate_sql(sanitize_sql(ref.options[:conditions], aliased_table_name))
+                end
               end
 
               @join
diff --git a/activerecord/lib/active_record/associations/association_collection.rb b/activerecord/lib/active_record/associations/association_collection.rb
index 358db6df1d..64dd5cf629 100644
--- a/activerecord/lib/active_record/associations/association_collection.rb
+++ b/activerecord/lib/active_record/associations/association_collection.rb
@@ -58,11 +58,14 @@ module ActiveRecord
           find_scope = construct_scope[:find].slice(:conditions, :order)
 
           with_scope(:find => find_scope) do
-            relation = @reflection.klass.send(:construct_finder_arel, options)
+            relation = @reflection.klass.send(:construct_finder_arel, options, @reflection.klass.send(:current_scoped_methods))
 
             case args.first
-            when :first, :last, :all
+            when :first, :last
               relation.send(args.first)
+            when :all
+              records = relation.all
+              @reflection.options[:uniq] ? uniq(records) : records
             else
               relation.find(*args)
             end
@@ -402,7 +405,7 @@ module ActiveRecord
             end
           elsif @reflection.klass.scopes.include?(method)
             @reflection.klass.scopes[method].call(self, *args)
-          else          
+          else
             with_scope(construct_scope) do
               if block_given?
                 @reflection.klass.send(method, *args) { |*block_args| yield(*block_args) }
diff --git a/activerecord/lib/active_record/associations/has_many_through_association.rb b/activerecord/lib/active_record/associations/has_many_through_association.rb
index 214ce5959a..387b85aacd 100644
--- a/activerecord/lib/active_record/associations/has_many_through_association.rb
+++ b/activerecord/lib/active_record/associations/has_many_through_association.rb
@@ -51,8 +51,6 @@ module ActiveRecord
         end
 
         def construct_find_options!(options)
-          options[:select]  = construct_select(options[:select])
-          options[:from]  ||= construct_from
           options[:joins]   = construct_joins(options[:joins])
           options[:include] = @reflection.source_reflection.options[:include] if options[:include].nil? && @reflection.source_reflection.options[:include]
         end
diff --git a/activerecord/lib/active_record/associations/through_association_scope.rb b/activerecord/lib/active_record/associations/through_association_scope.rb
index 1924156e2a..1001199daa 100644
--- a/activerecord/lib/active_record/associations/through_association_scope.rb
+++ b/activerecord/lib/active_record/associations/through_association_scope.rb
@@ -6,8 +6,7 @@ module ActiveRecord
 
       def construct_scope
         { :create => construct_owner_attributes(@reflection),
-          :find   => { :from        => construct_from,
-                       :conditions  => construct_conditions,
+          :find   => { :conditions  => construct_conditions,
                        :joins       => construct_joins,
                        :include     => @reflection.options[:include] || @reflection.source_reflection.options[:include],
                        :select      => construct_select,
diff --git a/activerecord/lib/active_record/base.rb b/activerecord/lib/active_record/base.rb
index cc592aa2d3..7e4ee4b840 100755
--- a/activerecord/lib/active_record/base.rb
+++ b/activerecord/lib/active_record/base.rb
@@ -644,7 +644,7 @@ module ActiveRecord #:nodoc:
         options = args.extract_options!
         set_readonly_option!(options)
 
-        relation = construct_finder_arel(options)
+        relation = construct_finder_arel(options, current_scoped_methods)
 
         case args.first
         when :first, :last, :all
@@ -870,20 +870,21 @@ module ActiveRecord #:nodoc:
       #   # Update all books that match our conditions, but limit it to 5 ordered by date
       #   Book.update_all "author = 'David'", "title LIKE '%Rails%'", :order => 'created_at', :limit => 5
       def update_all(updates, conditions = nil, options = {})
-        scope = scope(:find)
-
         relation = active_relation
 
-        if conditions = construct_conditions(conditions, scope)
+        if conditions = construct_conditions(conditions, nil)
           relation = relation.where(Arel::SqlLiteral.new(conditions))
         end
 
-        relation = if options.has_key?(:limit) || (scope && scope[:limit])
+        relation = relation.limit(options[:limit]) if options[:limit].present?
+        relation = relation.order(options[:order]) if options[:order].present?
+
+        if current_scoped_methods && current_scoped_methods.limit_value.present? && current_scoped_methods.order_values.present?
           # Only take order from scope if limit is also provided by scope, this
           # is useful for updating a has_many association with a limit.
-          relation.order(construct_order(options[:order], scope)).limit(construct_limit(options[:limit], scope))
+          relation = current_scoped_methods.merge(relation) if current_scoped_methods
         else
-          relation.order(options[:order])
+          relation = current_scoped_methods.except(:limit, :order).merge(relation) if current_scoped_methods
         end
 
         relation.update(sanitize_sql_for_assignment(updates))
@@ -1572,26 +1573,26 @@ module ActiveRecord #:nodoc:
           end
         end
 
-        def construct_finder_arel(options = {}, scope = scope(:find))
+        def construct_finder_arel(options = {}, scope = nil)
           validate_find_options(options)
 
           relation = active_relation.
-            joins(construct_join(options[:joins], scope)).
-            where(construct_conditions(options[:conditions], scope)).
-            select(options[:select] || (scope && scope[:select]) || default_select(options[:joins] || (scope && scope[:joins]))).
-            group(options[:group] || (scope && scope[:group])).
-            having(options[:having] || (scope && scope[:having])).
-            order(construct_order(options[:order], scope)).
-            limit(construct_limit(options[:limit], scope)).
-            offset(construct_offset(options[:offset], scope)).
+            joins(options[:joins]).
+            where(options[:conditions]).
+            select(options[:select]).
+            group(options[:group]).
+            having(options[:having]).
+            order(options[:order]).
+            limit(options[:limit]).
+            offset(options[:offset]).
             from(options[:from]).
-            includes( merge_includes(scope && scope[:include], options[:include]))
-
-          lock = (scope && scope[:lock]) || options[:lock]
-          relation = relation.lock if lock.present?
+            includes(options[:include])
 
-          relation = relation.readonly if options[:readonly]
+          relation = relation.where(type_condition) if finder_needs_type_condition?
+          relation = relation.lock(options[:lock]) if options[:lock].present?
+          relation = relation.readonly(options[:readonly]) if options.has_key?(:readonly)
 
+          relation = scope.merge(relation) if scope
           relation
         end
 
@@ -1665,10 +1666,10 @@ module ActiveRecord #:nodoc:
           relation = active_relation.table
           join_dependency.join_associations.map { |association|
             if (association_relation = association.relation).is_a?(Array)
-              [Arel::InnerJoin.new(relation, association_relation.first, association.association_join.first).joins(relation),
-              Arel::InnerJoin.new(relation, association_relation.last, association.association_join.last).joins(relation)].join()
+              [Arel::InnerJoin.new(relation, association_relation.first, *association.association_join.first).joins(relation),
+              Arel::InnerJoin.new(relation, association_relation.last, *association.association_join.last).joins(relation)].join()
             else
-              Arel::InnerJoin.new(relation, association_relation, association.association_join).joins(relation)
+              Arel::InnerJoin.new(relation, association_relation, *association.association_join).joins(relation)
             end
           }.join(" ")
         end
@@ -1713,7 +1714,7 @@ module ActiveRecord #:nodoc:
             super unless all_attributes_exists?(attribute_names)
             if match.finder?
               options = arguments.extract_options!
-              relation = options.any? ? construct_finder_arel(options) : scoped
+              relation = options.any? ? construct_finder_arel(options, current_scoped_methods) : scoped
               relation.send :find_by_attributes, match, attribute_names, *arguments
             elsif match.instantiator?
               scoped.send :find_or_instantiator_by_attributes, match, attribute_names, *arguments, &block
@@ -1830,52 +1831,49 @@ module ActiveRecord #:nodoc:
         def with_scope(method_scoping = {}, action = :merge, &block)
           method_scoping = method_scoping.method_scoping if method_scoping.respond_to?(:method_scoping)
 
-          # Dup first and second level of hash (method and params).
-          method_scoping = method_scoping.inject({}) do |hash, (method, params)|
-            hash[method] = (params == true) ? params : params.dup
-            hash
-          end
+          if method_scoping.is_a?(Hash)
+            # Dup first and second level of hash (method and params).
+            method_scoping = method_scoping.inject({}) do |hash, (method, params)|
+              hash[method] = (params == true) ? params : params.dup
+              hash
+            end
 
-          method_scoping.assert_valid_keys([ :find, :create ])
+            method_scoping.assert_valid_keys([ :find, :create ])
 
-          if f = method_scoping[:find]
-            f.assert_valid_keys(VALID_FIND_OPTIONS)
-            set_readonly_option! f
-          end
+            if f = method_scoping[:find]
+              f.assert_valid_keys(VALID_FIND_OPTIONS)
+              set_readonly_option! f
+            end
 
-          # Merge scopings
-          if [:merge, :reverse_merge].include?(action) && current_scoped_methods
-            method_scoping = current_scoped_methods.inject(method_scoping) do |hash, (method, params)|
-              case hash[method]
-                when Hash
-                  if method == :find
-                    (hash[method].keys + params.keys).uniq.each do |key|
-                      merge = hash[method][key] && params[key] # merge if both scopes have the same key
-                      if key == :conditions && merge
-                        if params[key].is_a?(Hash) && hash[method][key].is_a?(Hash)
-                          hash[method][key] = merge_conditions(hash[method][key].deep_merge(params[key]))
-                        else
-                          hash[method][key] = merge_conditions(params[key], hash[method][key])
-                        end
-                      elsif key == :include && merge
-                        hash[method][key] = merge_includes(hash[method][key], params[key]).uniq
-                      elsif key == :joins && merge
-                        hash[method][key] = merge_joins(params[key], hash[method][key])
-                      else
-                        hash[method][key] = hash[method][key] || params[key]
-                      end
-                    end
-                  else
-                    if action == :reverse_merge
-                      hash[method] = hash[method].merge(params)
-                    else
-                      hash[method] = params.merge(hash[method])
-                    end
-                  end
-                else
-                  hash[method] = params
+            relation = construct_finder_arel(method_scoping[:find] || {})
+
+            if current_scoped_methods && current_scoped_methods.create_with_value && method_scoping[:create]
+              scope_for_create = case action
+              when :merge
+                current_scoped_methods.create_with_value.merge(method_scoping[:create])
+              when :reverse_merge
+                method_scoping[:create].merge(current_scoped_methods.create_with_value)
+              else
+                method_scoping[:create]
               end
-              hash
+
+              relation = relation.create_with(scope_for_create)
+            else
+              scope_for_create = method_scoping[:create]
+              scope_for_create ||= current_scoped_methods.create_with_value if current_scoped_methods
+              relation = relation.create_with(scope_for_create) if scope_for_create
+            end
+
+            method_scoping = relation
+          end
+
+          if current_scoped_methods
+            case action
+            when :merge
+              method_scoping = current_scoped_methods.merge(method_scoping)
+            when :reverse_merge
+              method_scoping = current_scoped_methods.except(:where).merge(method_scoping)
+              method_scoping = method_scoping.merge(current_scoped_methods.only(:where))
             end
           end
 
@@ -1904,20 +1902,22 @@ module ActiveRecord #:nodoc:
         #     default_scope :order => 'last_name, first_name'
         #   end
         def default_scope(options = {})
-          self.default_scoping << { :find => options, :create => options[:conditions].is_a?(Hash) ? options[:conditions] : {} }
+          self.default_scoping << construct_finder_arel(options)
         end
 
         # Test whether the given method and optional key are scoped.
         def scoped?(method, key = nil) #:nodoc:
-          if current_scoped_methods && (scope = current_scoped_methods[method])
-            !key || !scope[key].nil?
+          case method
+          when :create
+            current_scoped_methods.send(:scope_for_create).present? if current_scoped_methods
           end
         end
 
         # Retrieve the scope for the given method and optional key.
         def scope(method, key = nil) #:nodoc:
-          if current_scoped_methods && (scope = current_scoped_methods[method])
-            key ? scope[key] : scope
+          case method
+          when :create
+            current_scoped_methods.send(:scope_for_create) if current_scoped_methods
           end
         end
 
diff --git a/activerecord/lib/active_record/calculations.rb b/activerecord/lib/active_record/calculations.rb
index 20d287faeb..bbb5922e0e 100644
--- a/activerecord/lib/active_record/calculations.rb
+++ b/activerecord/lib/active_record/calculations.rb
@@ -46,19 +46,19 @@ module ActiveRecord
       def count(*args)
         case args.size
         when 0
-          construct_calculation_arel.count
+          construct_calculation_arel({}, current_scoped_methods).count
         when 1
           if args[0].is_a?(Hash)
             options = args[0]
             distinct = options.has_key?(:distinct) ? options.delete(:distinct) : false
-            construct_calculation_arel(options).count(options[:select], :distinct => distinct)
+            construct_calculation_arel(options, current_scoped_methods).count(options[:select], :distinct => distinct)
           else
-            construct_calculation_arel.count(args[0])
+            construct_calculation_arel({}, current_scoped_methods).count(args[0])
           end
         when 2
           column_name, options = args
           distinct = options.has_key?(:distinct) ? options.delete(:distinct) : false
-          construct_calculation_arel(options).count(column_name, :distinct => distinct)
+          construct_calculation_arel(options, current_scoped_methods).count(column_name, :distinct => distinct)
         else
           raise ArgumentError, "Unexpected parameters passed to count(): #{args.inspect}"
         end
@@ -141,7 +141,7 @@ module ActiveRecord
       #   Person.minimum(:age, :having => 'min(age) > 17', :group => :last_name) # Selects the minimum age for any family without any minors
       #   Person.sum("2 * age")
       def calculate(operation, column_name, options = {})
-        construct_calculation_arel(options).calculate(operation, column_name, options.slice(:distinct))
+        construct_calculation_arel(options, current_scoped_methods).calculate(operation, column_name, options.slice(:distinct))
       rescue ThrowResult
         0
       end
@@ -151,49 +151,74 @@ module ActiveRecord
           options.assert_valid_keys(CALCULATIONS_OPTIONS)
         end
 
-        def construct_calculation_arel(options = {})
+        def construct_calculation_arel(options = {}, merge_with_relation = nil)
           validate_calculation_options(options)
           options = options.except(:distinct)
 
-          scope = scope(:find)
-          includes = merge_includes(scope ? scope[:include] : [], options[:include])
+          includes = merge_includes(merge_with_relation ? merge_with_relation.includes_values : [], options[:include])
 
           if includes.any?
-            join_dependency = ActiveRecord::Associations::ClassMethods::JoinDependency.new(self, includes, construct_join(options[:joins], scope))
-            construct_calculation_arel_with_included_associations(options, join_dependency)
+            merge_with_joins = merge_with_relation ? merge_with_relation.joins_values : []
+            joins = (merge_with_joins + Array.wrap(options[:joins])).uniq
+            join_dependency = ActiveRecord::Associations::ClassMethods::JoinDependency.new(self, includes, construct_join(joins, nil))
+            construct_calculation_arel_with_included_associations(options, join_dependency, merge_with_relation)
           else
-            active_relation.
-              joins(construct_join(options[:joins], scope)).
-              from((scope && scope[:from]) || options[:from]).
-              where(construct_conditions(options[:conditions], scope)).
+            relation = active_relation.
+              joins(options[:joins]).
+              where(options[:conditions]).
               order(options[:order]).
               limit(options[:limit]).
               offset(options[:offset]).
               group(options[:group]).
-              having(options[:having]).
-              select(options[:select] || (scope && scope[:select]) || default_select(options[:joins] || (scope && scope[:joins])))
+              having(options[:having])
+
+            if merge_with_relation
+              relation = merge_with_relation.except(:select, :order, :limit, :offset, :group, :from).merge(relation)
+            else
+              relation = relation.where(type_condition) if finder_needs_type_condition?
+            end
+
+            from = merge_with_relation.from_value if merge_with_relation && merge_with_relation.from_value.present?
+            from = options[:from] if from.blank? && options[:from].present?
+            relation = relation.from(from)
+
+            select = options[:select].presence || (merge_with_relation ? merge_with_relation.select_values.join(", ") : nil)
+            relation = relation.select(select)
+
+            relation
           end
         end
 
-        def construct_calculation_arel_with_included_associations(options, join_dependency)
-          scope = scope(:find)
-
+        def construct_calculation_arel_with_included_associations(options, join_dependency, merge_with_relation = nil)
           relation = active_relation
 
           for association in join_dependency.join_associations
             relation = association.join_relation(relation)
           end
 
-          relation = relation.joins(construct_join(options[:joins], scope)).
+          if merge_with_relation
+            relation.joins_values = (merge_with_relation.joins_values + relation.joins_values).uniq
+            relation.where_values = merge_with_relation.where_values
+
+            merge_limit = merge_with_relation.taken
+          else
+            relation = relation.where(type_condition) if finder_needs_type_condition?
+          end
+
+          relation = relation.joins(options[:joins]).
             select(column_aliases(join_dependency)).
             group(options[:group]).
             having(options[:having]).
             order(options[:order]).
-            where(construct_conditions(options[:conditions], scope)).
-            from((scope && scope[:from]) || options[:from])
+            where(options[:conditions]).
+            from(options[:from])
+
+
+          if !using_limitable_reflections?(join_dependency.reflections) && (merge_limit || options[:limit])
+            relation = relation.where(construct_arel_limited_ids_condition(options, join_dependency))
+          end
 
-          relation = relation.where(construct_arel_limited_ids_condition(options, join_dependency)) if !using_limitable_reflections?(join_dependency.reflections) && ((scope && scope[:limit]) || options[:limit])
-          relation = relation.limit(construct_limit(options[:limit], scope)) if using_limitable_reflections?(join_dependency.reflections)
+          relation = relation.limit(options[:limit] || merge_limit) if using_limitable_reflections?(join_dependency.reflections)
 
           relation
         end
diff --git a/activerecord/lib/active_record/named_scope.rb b/activerecord/lib/active_record/named_scope.rb
index f63b249241..47b69dec62 100644
--- a/activerecord/lib/active_record/named_scope.rb
+++ b/activerecord/lib/active_record/named_scope.rb
@@ -26,10 +26,12 @@ module ActiveRecord
         if options.present?
           Scope.new(self, options, &block)
         else
-          unless scoped?(:find)
+          current_scope = current_scoped_methods
+
+          unless current_scope
             finder_needs_type_condition? ? active_relation.where(type_condition) : active_relation.spawn
           else
-            construct_finder_arel
+            construct_finder_arel({}, current_scoped_methods)
           end
         end
       end
diff --git a/activerecord/lib/active_record/relation.rb b/activerecord/lib/active_record/relation.rb
index 33127194b0..8a86d2e60a 100644
--- a/activerecord/lib/active_record/relation.rb
+++ b/activerecord/lib/active_record/relation.rb
@@ -47,17 +47,20 @@ module ActiveRecord
 
       @records = if find_with_associations
         begin
-          @klass.send(:find_with_associations, {
-            :select => arel.send(:select_clauses).join(', '),
+          options = {
+            :select => @select_values.any? ? @select_values.join(", ") : nil,
             :joins => arel.joins(arel),
-            :group => arel.send(:group_clauses).join(', '),
+            :group =>  @group_values.any? ? @group_values.join(", ") : nil,
             :order => order_clause,
             :conditions => where_clause,
             :limit => arel.taken,
             :offset => arel.skipped,
             :from => (arel.send(:from_clauses) if arel.send(:sources).present?)
-            },
-            ActiveRecord::Associations::ClassMethods::JoinDependency.new(@klass, @eager_load_values + @includes_values, nil))
+          }
+
+          including = (@eager_load_values + @includes_values).uniq
+          join_dependency = ActiveRecord::Associations::ClassMethods::JoinDependency.new(@klass, including, nil)
+          @klass.send(:find_with_associations, options, join_dependency)
         rescue ThrowResult
           []
         end
@@ -161,7 +164,7 @@ module ActiveRecord
     end
 
     def with_create_scope
-      @klass.send(:with_scope, :create => scope_for_create) { yield }
+      @klass.send(:with_scope, :create => scope_for_create, :find => {}) { yield }
     end
 
     def scope_for_create
diff --git a/activerecord/lib/active_record/relation/calculation_methods.rb b/activerecord/lib/active_record/relation/calculation_methods.rb
index e6f62ee49a..2477481ec8 100644
--- a/activerecord/lib/active_record/relation/calculation_methods.rb
+++ b/activerecord/lib/active_record/relation/calculation_methods.rb
@@ -40,7 +40,7 @@ module ActiveRecord
       distinct = options[:distinct] || distinct
       column_name = :all if column_name.blank? && operation == "count"
 
-      if arel.send(:groupings).any?
+      if @group_values.any?
         return execute_grouped_calculation(operation, column_name)
       else
         return execute_simple_calculation(operation, column_name, distinct)
@@ -63,7 +63,7 @@ module ActiveRecord
     end
 
     def execute_grouped_calculation(operation, column_name) #:nodoc:
-      group_attr      = arel.send(:groupings).first.value
+      group_attr      = @group_values.first
       association     = @klass.reflect_on_association(group_attr.to_sym)
       associated      = association && association.macro == :belongs_to # only count belongs_to associations
       group_field     = associated ? association.primary_key_name : group_attr
@@ -106,7 +106,6 @@ module ActiveRecord
       column_name = :all
 
       # Handles count(), count(:column), count(:distinct => true), count(:column, :distinct => true)
-      # TODO : relation.projections only works when .select() was last in the chain. Fix it!
       case args.size
       when 0
         select = get_projection_name_from_chained_relations
diff --git a/activerecord/lib/active_record/relation/query_methods.rb b/activerecord/lib/active_record/relation/query_methods.rb
index 7ceec40954..a3ac58bc81 100644
--- a/activerecord/lib/active_record/relation/query_methods.rb
+++ b/activerecord/lib/active_record/relation/query_methods.rb
@@ -10,8 +10,20 @@ module ActiveRecord
           def #{query_method}(*args)
             spawn.tap do |new_relation|
               new_relation.#{query_method}_values ||= []
-              value = args.size > 1 ? [args] : Array.wrap(args)
-              new_relation.#{query_method}_values += value
+              value = Array.wrap(args.flatten).reject {|x| x.blank? }
+              new_relation.#{query_method}_values += value if value.present?
+            end
+          end
+        CEVAL
+      end
+
+      [:where, :having].each do |query_method|
+        class_eval <<-CEVAL
+          def #{query_method}(*args)
+            spawn.tap do |new_relation|
+              new_relation.#{query_method}_values ||= []
+              value = build_where(*args)
+              new_relation.#{query_method}_values += [*value] if value.present?
             end
           end
         CEVAL
@@ -58,51 +70,83 @@ module ActiveRecord
     def build_arel
       arel = table
 
-      @joins_values.each do |j|
-        next if j.blank?
+      joined_associations = []
+      association_joins = []
+
+      joins = @joins_values.map {|j| j.respond_to?(:strip) ? j.strip : j}.uniq
+
+      # Build association joins first
+      joins.each do |join|
+        association_joins << join if [Hash, Array, Symbol].include?(join.class) && !@klass.send(:array_of_strings?, join)
+      end
+
+      if association_joins.any?
+        join_dependency = ActiveRecord::Associations::ClassMethods::JoinDependency.new(@klass, association_joins.uniq, nil)
+        to_join = []
+
+        join_dependency.join_associations.each do |association|
+          if (association_relation = association.relation).is_a?(Array)
+            to_join << [association_relation.first, association.association_join.first]
+            to_join << [association_relation.last, association.association_join.last]
+          else
+            to_join << [association_relation, association.association_join]
+          end
+        end
+
+        to_join.each do |tj|
+          unless joined_associations.detect {|ja| ja[0] == tj[0] && ja[1] == tj[1] }
+            joined_associations << tj
+            arel = arel.join(tj[0]).on(*tj[1])
+          end
+        end
+      end
+
+      joins.each do |join|
+        next if join.blank?
 
         @implicit_readonly = true
 
-        case j
+        case join
         when Relation::JoinOperation
-          arel = arel.join(j.relation, j.join_class).on(j.on)
+          arel = arel.join(join.relation, join.join_class).on(*join.on)
         when Hash, Array, Symbol
-          if @klass.send(:array_of_strings?, j)
-            arel = arel.join(j.join(' '))
-          else
-            arel = arel.join(@klass.send(:build_association_joins, j))
+          if @klass.send(:array_of_strings?, join)
+            join_string = join.join(' ')
+            arel = arel.join(join_string)
           end
         else
-          arel = arel.join(j)
+          arel = arel.join(join)
         end
       end
 
-      @where_values.each do |where|
-        if conditions = build_where(where)
-          arel = conditions.is_a?(String) ? arel.where(conditions) : arel.where(*conditions)
-        end
+      @where_values.uniq.each do |w|
+        arel = w.is_a?(String) ? arel.where(w) : arel.where(*w)
       end
 
-      @having_values.each do |where|
-        if conditions = build_where(where)
-          arel = conditions.is_a?(String) ? arel.having(conditions) : arel.having(*conditions)
-        end
+      @having_values.uniq.each do |h|
+        arel = h.is_a?(String) ? arel.having(h) : arel.having(*h)
       end
 
       arel = arel.take(@limit_value) if @limit_value.present?
       arel = arel.skip(@offset_value) if @offset_value.present?
 
-      @group_values.each do |g|
+      @group_values.uniq.each do |g|
         arel = arel.group(g) if g.present?
       end
 
-      @order_values.each do |o|
+      @order_values.uniq.each do |o|
         arel = arel.order(o) if o.present?
       end
 
-      @select_values.each do |s|
-        @implicit_readonly = false
-        arel = arel.project(s) if s.present?
+      selects = @select_values.uniq
+
+      if selects.present?
+        selects.each do |s|
+          @implicit_readonly = false
+          arel = arel.project(s) if s.present?
+        end
+      elsif joins.present?
+        arel = arel.project(@klass.quoted_table_name + '.*')
       end
 
       arel = arel.from(@from_value) if @from_value.present?
@@ -120,7 +164,7 @@ module ActiveRecord
     def build_where(*args)
       return if args.blank?
 
-      builder = PredicateBuilder.new(Arel::Sql::Engine.new(@klass))
+      builder = PredicateBuilder.new(table.engine)
 
       conditions = if [String, Array].include?(args.first.class)
         merged = @klass.send(:merge_conditions, args.size > 1 ? Array.wrap(args) : args.first)
diff --git a/activerecord/lib/active_record/relation/spawn_methods.rb b/activerecord/lib/active_record/relation/spawn_methods.rb
index 66eae69d92..a248c72715 100644
--- a/activerecord/lib/active_record/relation/spawn_methods.rb
+++ b/activerecord/lib/active_record/relation/spawn_methods.rb
@@ -19,21 +19,19 @@ module ActiveRecord
 
       merged_relation = spawn.eager_load(r.eager_load_values).preload(r.preload_values).includes(r.includes_values)
 
-      merged_relation.readonly_value = r.readonly_value unless merged_relation.readonly_value
-      merged_relation.limit_value = r.limit_value unless merged_relation.limit_value
+      merged_relation.readonly_value = r.readonly_value unless r.readonly_value.nil?
+      merged_relation.limit_value = r.limit_value if r.limit_value.present?
       merged_relation.lock_value = r.lock_value unless merged_relation.lock_value
+      merged_relation.offset_value = r.offset_value if r.offset_value.present?
 
       merged_relation = merged_relation.
         joins(r.joins_values).
         group(r.group_values).
-        offset(r.offset_value).
         select(r.select_values).
         from(r.from_value).
         having(r.having_values)
 
-      relation_order = r.order_values
-      merged_order = relation_order.present? ? relation_order : order_values
-      merged_relation.order_values = merged_order
+      merged_relation.order_values = Array.wrap(order_values) + Array.wrap(r.order_values)
 
       merged_relation.create_with_value = @create_with_value
 
@@ -50,7 +48,7 @@ module ActiveRecord
           merged_wheres = merged_wheres.reject {|p| p.is_a?(Arel::Predicates::Equality) && p.operand1.name == w.operand1.name }
         end
 
-        merged_wheres << w
+        merged_wheres += [w]
       end
 
       merged_relation.where_values = merged_wheres
@@ -74,5 +72,21 @@ module ActiveRecord
       result
     end
 
+    def only(*onlies)
+      result = Relation.new(@klass, table)
+
+      onlies.each do |only|
+        if (Relation::ASSOCIATION_METHODS + Relation::MULTI_VALUE_METHODS).include?(only)
+          result.send(:"#{only}_values=", send(:"#{only}_values"))
+        elsif Relation::SINGLE_VALUE_METHODS.include?(only)
+          result.send(:"#{only}_value=", send(:"#{only}_value"))
+        else
+          raise "Invalid argument : #{only}"
+        end
+      end
+
+      result
+    end
+
   end
 end