a more stable fix for slow SEL

lib/dm-core/associations/relationship.rb

@@ -149,8 +149,7 @@ def get_parent(child, parent = nil)
           unless collection.empty?
             collection.send(:lazy_load)
             children.each do |c|
-              p = parent_identity_map[child_key.get(c)] || collection.get(*child_key.get(c))
-              c.send(association_accessor).instance_variable_set(:@parent, p)
+              c.send(association_accessor).instance_variable_set(:@parent, collection.get(*child_key.get(c)))
             end
             child.send(association_accessor).instance_variable_get(:@parent)
           end

lib/dm-core/collection.rb

@@ -52,8 +52,8 @@ def reload(query = {})
     def get(*key)
       key = model.typecast_key(key)
       if loaded?
-        # loop over the collection to find the matching resource
-        detect { |resource| resource.key == key }
+        # find indexed resource (create index first if it does not exist)
+        (@index||=map{|r| [r.key,r]}.to_hash)[key]
       elsif query.limit || query.offset > 0
         # current query is exclusive, find resource within the set
 
@@ -533,6 +533,7 @@ def add(resource)
     def relate_resource(resource)
       return unless resource
       resource.collection = self
+      wipe_index
       resource
     end
 
@@ -541,6 +542,7 @@ def relate_resource(resource)
     def orphan_resource(resource)
       return unless resource
       resource.collection = nil if resource.collection == self
+      wipe_index
       resource
     end
 
@@ -578,6 +580,10 @@ def keys
     def identity_map
       repository.identity_map(model)
     end
+
+    def wipe_index
+      @index = nil
+    end
 
     ##
     # @api private