be a bit more specific when a way is a member of a relation. Actually return an error message when a relation precondition fails. Remove a debug statement.

app/models/relation.rb

@@ -288,7 +288,6 @@ class Relation < ActiveRecord::Base
     elements = { :node => Hash.new, :way => Hash.new, :relation => Hash.new }
     self.members.each do |m|
       # find the hash for the element type or die
-      logger.debug m[0]
       hash = elements[m[0].downcase.to_sym] or return false
       # unless its in the cache already
       unless hash.key? m[1]
@@ -299,6 +298,7 @@ class Relation < ActiveRecord::Base
 
         # and check that it is OK to use.
         unless element and element.visible? and element.preconditions_ok?
+          raise OSM::APIPreconditionFailedError.new("Relation with id #{self.id} cannot be saved due to #{m[0]} with id #{element.id}")
           return false
         end
         hash[m[1]] = true

app/models/way.rb

@@ -251,18 +251,17 @@ class Way < ActiveRecord::Base
     # shouldn't be possible to get race conditions.
     Way.transaction do
       check_consistency(self, new_way, user)
-      if RelationMember.find(:first, :joins => :relation,
+      rel = RelationMember.find(:first, :joins => :relation,
                              :conditions => [ "visible = ? AND member_type='Way' and member_id=? ", true, self.id])
-        raise OSM::APIPreconditionFailedError.new("You need to make sure that the way with id: #{self.id} is not a member of a relation.")
-      else
-        self.changeset_id = new_way.changeset_id
-        self.changeset = new_way.changeset
+      raise OSM::APIPreconditionFailedError.new("You need to make sure that the way with id: #{self.id} is not a member of the relation with id #{rel.id}.") if rel
+      
+      self.changeset_id = new_way.changeset_id
+      self.changeset = new_way.changeset
 
-        self.tags = []
-        self.nds = []
-        self.visible = false
-        save_with_history!
-      end
+      self.tags = []
+      self.nds = []
+      self.visible = false
+      save_with_history!
     end
   end