#{through_names.join(', ')} are :through associations and do

Error message

#{through_names.join(', ')} are :through associations and do not support $lookup-based eager loading. All inclusions for this query will be preloaded using separate queries.

What it means

Error "#{through_names.join(', ')} are :through associations and do not support $lookup-based eager loading. All inclusions for this query will be preloaded using separate queries." thrown in mongodb/mongoid.

Source

Thrown at lib/mongoid/association/eager_loadable.rb:60

            "#{offender.name} (client: #{offender.klass.client_name}, database: #{offender.klass.database_name})"
          end
          Mongoid.logger.warn(
            'eager_load cannot use $lookup aggregation because the following associations ' \
            "reside in a different cluster or database than #{klass} " \
            "(client: #{klass.client_name}, database: #{klass.database_name}): " \
            "#{offender_descriptions.join(', ')}. Falling back to #includes behavior."
          )
          return eager_load(docs_for_lookup_fallback)
        end

        through_inclusions = criteria.inclusions.select do |association|
          association.is_a?(Association::Referenced::HasOneThrough) ||
            association.is_a?(Association::Referenced::HasManyThrough)
        end

        if through_inclusions.any?
          through_names = through_inclusions.map { |association| ":#{association.name}" }
          Mongoid.logger.warn(
            "#{through_names.join(', ')} are :through associations and do not support " \
            '$lookup-based eager loading. All inclusions for this query will be preloaded ' \
            'using separate queries.'
          )
          return eager_load(docs_for_lookup_fallback)
        end

        documents = preload_for_lookup(criteria)
        # A polymorphic belongs_to cannot be expressed as a $lookup: its target
        # collection varies per document. It is resolved after the roots are
        # materialized, each inclusion by its own preloader.
        criteria.inclusions.select(&:polymorphic?).each do |association|
          EagerLoad::PolymorphicPreloader.new(association, klass).preload_into(documents)
        end
        documents
      end

      # Load the associations for the given documents. This will be done

View on GitHub (pinned to 0da0e23d71)

When it happens

Trigger: Thrown at lib/mongoid/association/eager_loadable.rb:60 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/ef5c0f475359e41f. Report an issue: GitHub.