Check if index exists before removing it (#12713).

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@11137 e93f8b46-1217-0410-a6f0-8f06a7374b81

db/migrate/091_change_changesets_revision_to_string.rb

@@ -1,13 +1,32 @@
 class ChangeChangesetsRevisionToString < ActiveRecord::Migration
   def self.up
-    remove_index  :changesets, :name => :changesets_repos_rev
+    # Some backends (eg. SQLServer 2012) do not support changing the type
+    # of an indexed column so the index needs to be dropped first
+    # BUT this index is renamed with some backends (at least SQLite3) for
+    # some (unknown) reasons, thus we check for the other name as well
+    # so we don't end up with 2 identical indexes
+    if index_exists? :changesets, [:repository_id, :revision], :name => :changesets_repos_rev
+      remove_index  :changesets, :name => :changesets_repos_rev
+    end
+    if index_exists? :changesets, [:repository_id, :revision], :name => :altered_changesets_repos_rev
+      remove_index  :changesets, :name => :altered_changesets_repos_rev
+    end
+
     change_column :changesets, :revision, :string, :null => false
+
     add_index :changesets, [:repository_id, :revision], :unique => true, :name => :changesets_repos_rev
   end
 
   def self.down
-    remove_index  :changesets, :name => :changesets_repos_rev
+    if index_exists? :changesets, :changesets_repos_rev
+      remove_index  :changesets, :name => :changesets_repos_rev
+    end
+    if index_exists? :changesets, [:repository_id, :revision], :name => :altered_changesets_repos_rev
+      remove_index  :changesets, :name => :altered_changesets_repos_rev
+    end
+
     change_column :changesets, :revision, :integer, :null => false
+
     add_index :changesets, [:repository_id, :revision], :unique => true, :name => :changesets_repos_rev
   end
 end