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

Attempted to access attribute

Error message

Attempted to access attribute '%{name}' on %{klass} which was not loaded.

What it means

get_relation raises this when the association's underlying attribute is missing from the document's loaded attributes, typically because the document came from a projection (only/without) that excluded the key. Mongoid deliberately raises only for embedded associations, never for internal retrievals.

Solutions

  1. Reload the document without the field projection so the association key is loaded
  2. Include the association's foreign key field in the only/fields selection
Defensive patterns

Strategy: retry

When it happens

Trigger: Thrown at lib/mongoid/association/accessors.rb:120 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/bc4add5d2f62dad1. Report an issue: GitHub.

Appendix: source

Thrown at lib/mongoid/association/accessors.rb:120

      # @param [ true | false ] reload If the association is to be reloaded.
      #
      # @return [ Proxy ] The association.
      def get_relation(name, association, object, reload = false)
        field_name = database_field_name(name)

        # As per the comments under MONGOID-5034, I've decided to only raise on
        # embedded associations for a missing attribute. Rails does not raise
        # for a missing attribute on referenced associations.
        # We also don't want to raise if we're retrieving an association within
        # the codebase. This is often done when retrieving the inverse association
        # during binding or when cascading callbacks. Whenever we retrieve
        # associations within the codebase, we use without_autobuild.
        if !without_autobuild? && association.embedded? && attribute_missing?(field_name)
          # We always allow accessing the parent document of an embedded one.
          try_get_parent = association.is_a?(
            Mongoid::Association::Embedded::EmbeddedIn
          ) && field_name == association.key
          raise Mongoid::Errors::AttributeNotLoaded.new(self.class, field_name) unless try_get_parent
        end

        if !reload && (value = ivar(name)) != false
          value
        else
          _building do
            _loading do
              if object && needs_no_database_query?(object, association)
                __build__(name, object, association)
              # Check if data was loaded via $lookup aggregation
              elsif !association.embedded? && attributes.key?(name.to_s)
                # Use the pre-loaded association data from $lookup
                __build__(name, attributes[name.to_s], association)
              else
                selected_fields = _mongoid_filter_selected_fields(association.key)
                __build__(name, attributes[association.key], association, selected_fields)
              end
            end

View on GitHub (pinned to 0da0e23d71)