You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: backend_enum_source.rb
    path of file: ./repos/archivesspace/backend/app/model
    
    the code of the file until where you have to start completion: require 'rufus/lru'

class BackendEnumSource

  def self.valid?(enum_name, value)
    if RequestContext.get(:create_enums)
      # Some cheeky caching on the RequestContext here.  The batch import
      # process can need to check/create an awful lot of enums, so don't insert
      # into the database unless we really need to.
      #
      created = RequestContext.get(:created_enums) || {}
      RequestContext.put(:created_enums, created)

      if !Array(created[enum_name]).include?(value)
        # The customer i
    
  def self.valid?(enum_name, value)
    if RequestContext.get(:create_enums)
      # Some cheeky caching on the RequestContext here.  The batch import
      # process can need to check/create an awful lot of enums, so don't insert
      # into the database unless we really need to.
      #
      created = RequestContext.get(:created_enums) || {}
      RequestContext.put(:created_enums, created)

      if !Array(created[enum_name]).include?(value)
        # The customer is always right!
        DB.open(true) do |db|
          enum_id = db[:enumeration].filter(:name => enum_name).select(:id).first[:id]

          raise "Couldn't find enum: #{enum_name}" if !enum_id

          DB.attempt {
            sibling = db[:enumeration_value].filter(:enumeration_id => enum_id).order(:position).last
            if sibling
              position = sibling[:position] + 1
            else
              position = 0
            end

            db[:enumeration_value].insert(:enumeration_id => enum_id,
                                          :value => value,
                                          :position => position)
            @@enum_value_cache.delete(enum_name)
            Enumeration.broadcast_changes
          }.and_if_constraint_fails do
            # Must already be there.  No problem.
          end
        end

        created[enum_name] ||= []
        created[enum_name] << value
      end