add_pg_decoders

# File activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb, line 789
        def add_pg_decoders
          coders_by_name = {
            'int2' => PG::TextDecoder::Integer,
            'int4' => PG::TextDecoder::Integer,
            'int8' => PG::TextDecoder::Integer,
            'oid' => PG::TextDecoder::Integer,
            'float4' => PG::TextDecoder::Float,
            'float8' => PG::TextDecoder::Float,
            'bool' => PG::TextDecoder::Boolean,
          }
          known_coder_types = coders_by_name.keys.map { |n| quote(n) }
          query =             SELECT t.oid, t.typname            FROM pg_type as t            WHERE t.typname IN (%s) % known_coder_types.join(", ")
          coders = execute_and_clear(query, "SCHEMA", []) do |result|
            result
              .map { |row| construct_coder(row, coders_by_name[row['typname']]) }
              .compact
          end

          map = PG::TypeMapByOid.new
          coders.each { |coder| map.add_coder(coder) }
          @connection.type_map_for_results = map
        end