Added where option to add_index to support postgresql partial indices

The `add_index` method now supports a `where` option that receives a
string with the partial index criteria.

    add_index(:accounts, :code, :where => "active")

    Generates

    CREATE INDEX index_accounts_on_code ON accounts(code) WHERE active

1 files changed, 5 insertions, 0 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
index edea414db7..dd421b2054 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
@@ -142,6 +142,11 @@ module ActiveRecord
         false
       end
 
+      # Does this adapter support partial indices?
+      def supports_partial_index?
+        false
+      end
+
       # Does this adapter support explain? As of this writing sqlite3,
       # mysql2, and postgresql are the only ones that do.
       def supports_explain?