Do not pre-fetch the primary key if multiple primary keys exist

Author: andfx

lib/arjdbc/oracle/adapter.rb

@@ -508,7 +508,7 @@ def select(sql, name = nil, binds = [])
     def prefetch_primary_key?(table_name = nil)
       return true if table_name.nil?
       table_name = table_name.to_s
-      columns(table_name).detect { |column| column.primary }
+      columns(table_name).count { |column| column.primary } == 1
     end
 
     # @override