find_primary_key

# File activerecord/lib/arel/visitors/mssql.rb, line 148
        def find_primary_key(o)
          @primary_keys[o.name] ||= begin
            primary_key_name = @connection.primary_key(o.name)
            # some tables might be without primary key
            primary_key_name && o[primary_key_name]
          end
        end