What causes "#{data_type} is not supported by this adapter" in flippercloud/flipper?

Align versions: bundle update flipper flipper-sequel so the adapter release matches flipper core (they ship in lockstep).

flippercloud/flipper · error · RuntimeError

#{data_type} is not supported by this adapter

Error message

#{data_type} is not supported by this adapter

What it means

flipper-sequel persists features in the flipper_features and flipper_gates tables, choosing the write per the gate's data type; enable, disable, and result_for_feature route unknown data types to unsupported_data_type, which raises (lib/flipper/adapters/sequel.rb:173-176). The supported set is :boolean, :integer, :set and :json — the expression gate reports :json. flipper-sequel is a separate gem from flipper core, so the usual cause is a lockfile pairing newer core (expression gates) with an older adapter release lacking the :json branch.

Source

Thrown at lib/flipper/adapters/sequel.rb:175

        when :boolean
          clear(feature)
        when :integer
          set(feature, gate, thing)
        when :json
          delete(feature, gate)
        when :set
          @gate_class.where(gate_attrs(feature, gate, thing, json: gate.data_type == :json)).delete
        else
          unsupported_data_type gate.data_type
        end

        true
      end

      private

      def unsupported_data_type(data_type)
        raise "#{data_type} is not supported by this adapter"
      end

      def set(feature, gate, thing, options = {})
        clear_feature = options.fetch(:clear, false)
        json_feature = options.fetch(:json, false)

        raise VALUE_TO_TEXT_WARNING if json_feature && value_not_text?

        @gate_class.db.transaction do
          clear(feature) if clear_feature
          delete(feature, gate)

          begin
            @gate_class.create(gate_attrs(feature, gate, thing, json: json_feature))
          rescue ::Sequel::UniqueConstraintViolation
          end
        end
      end

View on GitHub (pinned to 1f86de3ec9)

Solutions

Align versions: bundle update flipper flipper-sequel so the adapter release matches flipper core (they ship in lockstep).
Assert at boot that Gem.loaded_specs['flipper-sequel'].version equals Gem.loaded_specs['flipper'].version.
If a newer writer already stored expression rows, clear those features (feature.delete via a current-version process) so old readers stop raising on get.
Avoid expression rollouts until every process touching the database runs the aligned versions; map custom gates to supported data types.

Example fix

# before
gem 'flipper',        '~> 0.28.0'
gem 'flipper-sequel', '~> 0.25.0'

# after
gem 'flipper',        '~> 0.28.0'
gem 'flipper-sequel', '~> 0.28.0'

Defensive patterns

Strategy: validation

Validate before calling

def assert_flipper_gems_aligned!
  core = Gem.loaded_specs.fetch('flipper').version
  adapter = Gem.loaded_specs.fetch('flipper-sequel').version
  raise "flipper-sequel #{adapter} != flipper #{core}; align both gems" unless core == adapter
end

assert_flipper_gems_aligned! # at boot, before any expression operations

Type guard

def expression_writable?
  Gem.loaded_specs.fetch('flipper-sequel').version == Gem.loaded_specs.fetch('flipper').version
end

Try / catch

begin
  feature.enable_expression(expr)
rescue RuntimeError => e
  raise unless e.message.end_with?('is not supported by this adapter')
  Flipper.logger.warn('flipper-sequel lacks :json support; using percentage rollout instead')
  feature.enable_percentage_of_time(10)
end

Prevention

Pin flipper and flipper-sequel to identical versions and bump them atomically.
Boot-assert version equality in web and job processes that share the database.
Sequence rollouts: upgrade all Sequel-reading processes before enabling expressions anywhere.
Run bundle exec rake with a spec that calls feature.enabled? after upgrades to catch read-path raises early.

When it happens

Trigger: feature.enable_expression(...) / feature.add_expression (or Cloud/UI-driven expression writes) while flipper-sequel resolves older than flipper core — enable/disable raise ':json is not supported by this adapter'; feature.enabled? on a feature that already has expression rows raises via result_for_feature. Custom gates with data types outside %i[boolean integer set json] trigger it on any release.

Common situations: Rails apps that bump flipper but not flipper-sequel; multi-process setups (web + background jobs) sharing the same database where one process already wrote expression gate rows; adding a custom gate type to a fork.

Related errors

AI-assisted analysis of flippercloud/flipper@1f86de3ec9 (2026-08-23). Data as JSON: /api/errors/3fe868f926218058. Report an issue: GitHub.