pk_and_sequence_for

# File activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb, line 946
      def pk_and_sequence_for(table) #:nodoc:
        # First try looking for a sequence with a dependency on the
        # given table's primary key.
        result = query(          SELECT attr.attname, seq.relname          FROM pg_class      seq,               pg_attribute  attr,               pg_depend     dep,               pg_namespace  name,               pg_constraint cons          WHERE seq.oid           = dep.objid            AND seq.relkind       = 'S'            AND attr.attrelid     = dep.refobjid            AND attr.attnum       = dep.refobjsubid            AND attr.attrelid     = cons.conrelid            AND attr.attnum       = cons.conkey[1]            AND cons.contype      = 'p'            AND dep.refobjid      = '#{quote_table_name(table)}'::regclass, 'PK and serial sequence')[0]

        if result.nil? or result.empty?
          # If that fails, try parsing the primary key's default value.
          # Support the 7.x and 8.0 nextval('foo'::text) as well as
          # the 8.1+ nextval('foo'::regclass).
          result = query(            SELECT attr.attname,              CASE                WHEN split_part(def.adsrc, '''', 2) ~ '.' THEN                  substr(split_part(def.adsrc, '''', 2),                         strpos(split_part(def.adsrc, '''', 2), '.')+1)                ELSE split_part(def.adsrc, '''', 2)              END            FROM pg_class       t            JOIN pg_attribute   attr ON (t.oid = attrelid)            JOIN pg_attrdef     def  ON (adrelid = attrelid AND adnum = attnum)            JOIN pg_constraint  cons ON (conrelid = adrelid AND adnum = conkey[1])            WHERE t.oid = '#{quote_table_name(table)}'::regclass              AND cons.contype = 'p'              AND def.adsrc ~* 'nextval', 'PK and custom sequence')[0]
        end

        [result.first, result.last]
      rescue
        nil
      end