Use changeset and user caches in Changeset#download

app/controllers/changeset_controller.rb

@@ -161,6 +161,10 @@ class ChangesetController < ApplicationController
       end
     end
 
+    # create changeset and user caches
+    changeset_cache = {}
+    user_display_name_cache = {}
+
     # create an osmChange document for the output
     result = OSM::API.new.get_xml_doc
     result.root.name = "osmChange"
@@ -173,16 +177,16 @@ class ChangesetController < ApplicationController
         if (elt.version == 1)
           # first version, so it must be newly-created.
           created = XML::Node.new "create"
-          created << elt.to_xml_node
+          created << elt.to_xml_node(changeset_cache, user_display_name_cache)
         else
           unless elt.visible
             # if the element isn't visible then it must have been deleted
             deleted = XML::Node.new "delete"
-            deleted << elt.to_xml_node
+            deleted << elt.to_xml_node(changeset_cache, user_display_name_cache)
           else
             # must be a modify
             modified = XML::Node.new "modify"
-            modified << elt.to_xml_node
+            modified << elt.to_xml_node(changeset_cache, user_display_name_cache)
           end
         end
     end

app/models/old_node.rb

@@ -42,9 +42,37 @@ class OldNode < ActiveRecord::Base
     return doc
   end
 
-  def to_xml_node
+  def to_xml_node(changeset_cache = {}, user_display_name_cache = {})
     el1 = XML::Node.new 'node'
     el1['id'] = self.node_id.to_s
+    el1['version'] = self.version.to_s
+    el1['changeset'] = self.changeset_id.to_s
+
+    if self.visible?
+      el1['lat'] = self.lat.to_s
+      el1['lon'] = self.lon.to_s
+    end
+
+    if changeset_cache.key?(self.changeset_id)
+      # use the cache if available
+    else
+      changeset_cache[self.changeset_id] = self.changeset.user_id
+    end
+
+    user_id = changeset_cache[self.changeset_id]
+
+    if user_display_name_cache.key?(user_id)
+      # use the cache if available
+    elsif self.changeset.user.data_public?
+      user_display_name_cache[user_id] = self.changeset.user.display_name
+    else
+      user_display_name_cache[user_id] = nil
+    end
+
+    if not user_display_name_cache[user_id].nil?
+      el1['user'] = user_display_name_cache[user_id]
+      el1['uid'] = user_id.to_s
+    end
 
     self.tags.each do |k,v|
       el2 = XML::Node.new('tag')
@@ -53,20 +81,8 @@ class OldNode < ActiveRecord::Base
       el1 << el2
     end
 
-    if self.visible?
-      el1['lat'] = self.lat.to_s
-      el1['lon'] = self.lon.to_s
-    end
-    
-    el1['changeset'] = self.changeset.id.to_s
-    if self.changeset.user.data_public?
-      el1['user'] = self.changeset.user.display_name
-      el1['uid'] = self.changeset.user.id.to_s
-    end
-
     el1['visible'] = self.visible.to_s
     el1['timestamp'] = self.timestamp.xmlschema
-    el1['version'] = self.version.to_s
     
     el1['redacted'] = self.redaction.id.to_s if self.redacted?
 

app/models/old_relation.rb

@@ -93,17 +93,34 @@ class OldRelation < ActiveRecord::Base
     return doc
   end
 
-  def to_xml_node
+  def to_xml_node(changeset_cache = {}, user_display_name_cache = {})
     el1 = XML::Node.new 'relation'
     el1['id'] = self.relation_id.to_s
     el1['visible'] = self.visible.to_s
     el1['timestamp'] = self.timestamp.xmlschema
-    if self.changeset.user.data_public?
-      el1['user'] = self.changeset.user.display_name
-      el1['uid'] = self.changeset.user.id.to_s
-    end
     el1['version'] = self.version.to_s
     el1['changeset'] = self.changeset_id.to_s
+
+    if changeset_cache.key?(self.changeset_id)
+      # use the cache if available
+    else
+      changeset_cache[self.changeset_id] = self.changeset.user_id
+    end
+
+    user_id = changeset_cache[self.changeset_id]
+
+    if user_display_name_cache.key?(user_id)
+      # use the cache if available
+    elsif self.changeset.user.data_public?
+      user_display_name_cache[user_id] = self.changeset.user.display_name
+    else
+      user_display_name_cache[user_id] = nil
+    end
+
+    if not user_display_name_cache[user_id].nil?
+      el1['user'] = user_display_name_cache[user_id]
+      el1['uid'] = user_id.to_s
+    end
     
     el1['redacted'] = self.redaction.id.to_s if self.redacted?
     

app/models/old_way.rb

@@ -92,17 +92,34 @@ class OldWay < ActiveRecord::Base
     @tags = t
   end
 
-  def to_xml_node
+  def to_xml_node(changeset_cache = {}, user_display_name_cache = {})
     el1 = XML::Node.new 'way'
     el1['id'] = self.way_id.to_s
     el1['visible'] = self.visible.to_s
     el1['timestamp'] = self.timestamp.xmlschema
-    if self.changeset.user.data_public?
-      el1['user'] = self.changeset.user.display_name
-      el1['uid'] = self.changeset.user.id.to_s
-    end
     el1['version'] = self.version.to_s
-    el1['changeset'] = self.changeset.id.to_s
+    el1['changeset'] = self.changeset_id.to_s
+
+    if changeset_cache.key?(self.changeset_id)
+      # use the cache if available
+    else
+      changeset_cache[self.changeset_id] = self.changeset.user_id
+    end
+
+    user_id = changeset_cache[self.changeset_id]
+
+    if user_display_name_cache.key?(user_id)
+      # use the cache if available
+    elsif self.changeset.user.data_public?
+      user_display_name_cache[user_id] = self.changeset.user.display_name
+    else
+      user_display_name_cache[user_id] = nil
+    end
+
+    if not user_display_name_cache[user_id].nil?
+      el1['user'] = user_display_name_cache[user_id]
+      el1['uid'] = user_id.to_s
+    end
 
     el1['redacted'] = self.redaction.id.to_s if self.redacted?