1 files changed, 33 insertions, 6 deletions
diff --git a/activerecord/lib/active_record/relation/spawn_methods.rb b/activerecord/lib/active_record/relation/spawn_methods.rb
index a248c72715..d5b13c6100 100644
--- a/activerecord/lib/active_record/relation/spawn_methods.rb
+++ b/activerecord/lib/active_record/relation/spawn_methods.rb
@@ -1,7 +1,7 @@
 module ActiveRecord
   module SpawnMethods
     def spawn(arel_table = self.table)
-      relation = Relation.new(@klass, arel_table)
+      relation = self.class.new(@klass, arel_table)
 
       (Relation::ASSOCIATION_METHODS + Relation::MULTI_VALUE_METHODS).each do |query_method|
         relation.send(:"#{query_method}_values=", send(:"#{query_method}_values"))
@@ -15,9 +15,10 @@ module ActiveRecord
     end
 
     def merge(r)
-      raise ArgumentError, "Cannot merge a #{r.klass.name} relation with #{@klass.name} relation" if r.klass != @klass
+      merged_relation = spawn
+      return merged_relation unless r
 
-      merged_relation = spawn.eager_load(r.eager_load_values).preload(r.preload_values).includes(r.includes_values)
+      merged_relation = merged_relation.eager_load(r.eager_load_values).preload(r.preload_values).includes(r.includes_values)
 
       merged_relation.readonly_value = r.readonly_value unless r.readonly_value.nil?
       merged_relation.limit_value = r.limit_value if r.limit_value.present?
@@ -31,7 +32,7 @@ module ActiveRecord
         from(r.from_value).
         having(r.having_values)
 
-      merged_relation.order_values = Array.wrap(order_values) + Array.wrap(r.order_values)
+      merged_relation.order_values = r.order_values if r.order_values.present?
 
       merged_relation.create_with_value = @create_with_value
 
@@ -59,7 +60,7 @@ module ActiveRecord
     alias :& :merge
 
     def except(*skips)
-      result = Relation.new(@klass, table)
+      result = self.class.new(@klass, table)
 
       (Relation::ASSOCIATION_METHODS + Relation::MULTI_VALUE_METHODS).each do |method|
         result.send(:"#{method}_values=", send(:"#{method}_values")) unless skips.include?(method)
@@ -73,7 +74,7 @@ module ActiveRecord
     end
 
     def only(*onlies)
-      result = Relation.new(@klass, table)
+      result = self.class.new(@klass, table)
 
       onlies.each do |only|
         if (Relation::ASSOCIATION_METHODS + Relation::MULTI_VALUE_METHODS).include?(only)
@@ -88,5 +89,31 @@ module ActiveRecord
       result
     end
 
+    VALID_FIND_OPTIONS = [ :conditions, :include, :joins, :limit, :offset,
+                           :order, :select, :readonly, :group, :having, :from, :lock ]
+
+    def apply_finder_options(options)
+      relation = spawn
+      return relation unless options
+
+      options.assert_valid_keys(VALID_FIND_OPTIONS)
+
+      relation = relation.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(options[:include])
+
+      relation = relation.lock(options[:lock]) if options[:lock].present?
+      relation = relation.readonly(options[:readonly]) if options.has_key?(:readonly)
+
+      relation
+    end
+
   end
 end