mongodb/mongoid · error · Mongoid::Errors::NoClientsConfig

No clients configuration provided.

Error message

No clients configuration provided.

What it means

Raised by the private Config#clients= setter when Mongoid.configure is called with a nil or falsy clients configuration, i.e. no mongoid.yml clients section was loaded or no clients hash was passed to configure. It signals that Mongoid cannot proceed without at least one client definition.

Solutions

1. Provide a clients hash containing a :default entry in mongoid.yml
2. Ensure the environment key in mongoid.yml matches the current environment

When it happens

Trigger: Thrown at lib/mongoid/config.rb:527 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of mongodb/mongoid@0da0e23d71 (2026-08-23). Data as JSON: /api/errors/ea75cda1eccb45c9. Report an issue: GitHub.

Appendix: source

Thrown at lib/mongoid/config.rb:527

    #
    # @return [ true | false ] If the app is deployed on Passenger.
    #
    # @deprecated
    def running_with_passenger?
      @running_with_passenger ||= defined?(PhusionPassenger)
    end

    Mongoid.deprecate(self, :running_with_passenger?)

    private

    def set_log_levels
      Mongoid.logger.level = Mongoid::Config.log_level unless defined?(::Rails)
      Mongo::Logger.logger.level = Mongoid.logger.level
    end

    def clients=(clients)
      raise Errors::NoClientsConfig.new unless clients

      c = clients.with_indifferent_access
      Validators::Client.validate(c)
      @clients = c
    end

    # Get database client that respects global overrides
    # Config.override_database and Config.override_client.
    #
    # @return [Mongo::Client] Client according to global overrides.
    def global_client
      client = if Threaded.client_override
                 Clients.with_name(Threaded.client_override)
               else
                 Clients.default
               end
      if Threaded.database_override
        client.use(Threaded.database_override)

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