rails_port_0.5: 006_remove_segments:

- Don't run the helper if there are no segments.
- s/DELETE FROM/TRUNCATE/

db/migrate/006_remove_segments.rb

@@ -2,6 +2,9 @@ require 'lib/migrate'
 
 class RemoveSegments < ActiveRecord::Migration
   def self.up
+    have_segs = select_value("SELECT count(*) FROM current_segments").to_i != 0
+
+    if have_segs
       prefix = File.join Dir.tmpdir, "006_remove_segments.#{$$}."
 
       cmd = "db/migrate/006_remove_segments_helper"
@@ -21,6 +24,7 @@ class RemoveSegments < ActiveRecord::Migration
 	map { |base| prefix + base }
       ways, way_nodes, way_tags,
 	relations, relation_members, relation_tags = tempfiles
+    end
 
     drop_table :segments
     drop_table :way_segments
@@ -41,16 +45,17 @@ class RemoveSegments < ActiveRecord::Migration
     end
     add_primary_key :current_way_nodes, [:id, :sequence_id]
 
-    execute "DELETE FROM way_tags"
-    execute "DELETE FROM ways"
-    execute "DELETE FROM current_way_tags"
-    execute "DELETE FROM current_ways"
+    execute "TRUNCATE way_tags"
+    execute "TRUNCATE ways"
+    execute "TRUNCATE current_way_tags"
+    execute "TRUNCATE current_ways"
 
     # now get the data back
     csvopts = "FIELDS TERMINATED BY ',' ENCLOSED BY '\"' ESCAPED BY '\"' LINES TERMINATED BY '\\n'"
 
-    tempfiles.each { |fn| File.chmod 0644, fn }
+    tempfiles.each { |fn| File.chmod 0644, fn } if have_segs
 
+    if have_segs
       execute "LOAD DATA LOCAL INFILE '#{ways}' INTO TABLE ways #{csvopts} (id, user_id, timestamp) SET visible = 1, version = 1"
       execute "LOAD DATA LOCAL INFILE '#{way_nodes}' INTO TABLE way_nodes #{csvopts} (id, node_id, sequence_id) SET version = 1"
       execute "LOAD DATA LOCAL INFILE '#{way_tags}' INTO TABLE way_tags #{csvopts} (id, k, v) SET version = 1"
@@ -58,10 +63,12 @@ class RemoveSegments < ActiveRecord::Migration
       execute "INSERT INTO current_ways SELECT id, user_id, timestamp, visible FROM ways"
       execute "INSERT INTO current_way_nodes SELECT id, node_id, sequence_id FROM way_nodes"
       execute "INSERT INTO current_way_tags SELECT id, k, v FROM way_tags"
+    end
 
     # and then readd the index
     add_index :current_way_nodes, [:node_id], :name => "current_way_nodes_node_idx"
 
+    if have_segs
       execute "LOAD DATA LOCAL INFILE '#{relations}' INTO TABLE relations #{csvopts} (id, user_id, timestamp) SET visible = 1, version = 1"
       execute "LOAD DATA LOCAL INFILE '#{relation_members}' INTO TABLE relation_members #{csvopts} (id, member_type, member_id, member_role) SET version = 1"
       execute "LOAD DATA LOCAL INFILE '#{relation_tags}' INTO TABLE relation_tags #{csvopts} (id, k, v) SET version = 1"
@@ -71,8 +78,9 @@ class RemoveSegments < ActiveRecord::Migration
       execute "INSERT INTO current_relations SELECT id, user_id, timestamp, visible FROM relations"
       execute "INSERT INTO current_relation_members SELECT id, member_type, member_id, member_role FROM relation_members"
       execute "INSERT INTO current_relation_tags SELECT id, k, v FROM relation_tags"
+    end
 
-    tempfiles.each { |fn| File.unlink fn }
+    tempfiles.each { |fn| File.unlink fn } if have_segs
   end
 
   def self.down