instance method add_pg_decoders

# File activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb, line 1152
        def add_pg_decoders
          @mapped_default_timezone = nil
          @timestamp_decoder = nil

          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,
            "numeric" => PG::TextDecoder::Numeric,
            "bool" => PG::TextDecoder::Boolean,
            "timestamp" => PG::TextDecoder::TimestampUtc,
            "timestamptz" => PG::TextDecoder::TimestampWithTimeZone,
          }

          known_coder_types = coders_by_name.keys.map { |n| quote(n) }
          query = <<~SQL % known_coder_types.join(", ")
            SELECT t.oid, t.typname
            FROM pg_type as t
            WHERE t.typname IN (%s)
          SQL
          coders = execute_and_clear(query, "SCHEMA", [], allow_retry: true, materialize_transactions: false) do |result|
            result.filter_map { |row| construct_coder(row, coders_by_name[row["typname"]]) }
          end

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

          @type_map_for_results = PG::TypeMapByOid.new
          @type_map_for_results.default_type_map = map
          @type_map_for_results.add_coder(PG::TextDecoder::Bytea.new(oid: 17, name: "bytea"))
          @type_map_for_results.add_coder(MoneyDecoder.new(oid: 790, name: "money"))

          # extract timestamp decoder for use in update_typemap_for_default_timezone
          @timestamp_decoder = coders.find { |coder| coder.name == "timestamp" }
          update_typemap_for_default_timezone
        end