mongodb/mongoid · error · NotImplementedError

NotImplementedError

Error message

NotImplementedError

What it means

Abstract-method sentinel in the eager loading base class: Eager#preload must be implemented by each concrete eager-loadable subclass. The base implementation exists only to fail loudly when a subclass forgets to define its preload strategy.

Solutions

1. Implement #preload in the eager-loading subclass for the association type
2. Do not call Eager#preload on the abstract base class

When it happens

Trigger: Thrown at lib/mongoid/association/eager.rb:69 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/27981ccfeb1d9fb4. Report an issue: GitHub.

Appendix: source

Thrown at lib/mongoid/association/eager.rb:69

        end

        while shift_association
          preload
          @loaded << @docs.collect { |d| d.send(@association.name) if d.respond_to?(@association.name) }
        end
        @loaded.flatten
      end

      protected

      # Preload the current association.
      #
      # This method should be implemented in the subclass
      #
      # @example Preload the current association into the documents.
      #   loader.preload
      def preload
        raise NotImplementedError
      end

      # Preload the current association using $lookup aggregation.
      # This method executes the aggregation pipeline
      # and instantiates the documents.
      # @example Preload the current association using $lookup.
      #   loader.preload_with_lookup
      def preload_with_lookup
        # For $lookup aggregation, execute pipeline and instantiate documents
        owner_class = @associations.first.owner_class
        aggregated_docs = owner_class.collection.aggregate(@pipeline)
        aggregated_docs.each do |doc|
          parsed_doc = Factory.from_db(owner_class, doc)
          @docs << parsed_doc
        end
      end

      # Retrieves the documents referenced by the association, and

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