A potential veritas relation registry usable for switching between adapters and in-memory via configuration.

relation_registry.rb

class RelationRegistry
  include AbstractType

  # Initialize object
  #
  # @return [undefined]
  #
  # @api private
  #
  def initialize
    @map = {}
  end

  # Return in memory relation
  #
  # @example
  #   source = RelationSource::InMemory.new
  #   source.register(:foo, [[:id, String], [:foo, String]])
  #   source.get(:foo) # => <Veritas::Relation header=Veritas::Header ...>
  #
  # @param [Symbol] name
  #   the name of the base relation
  #
  # @return [Veritas::Relation]
  #
  # @raise [KeyError]
  #   
  #
  # @api private
  #
  def get(name)
    @map.fetch(name)
  end

  # Register relation
  #
  # @param [Symbol] name
  #   the name to track relation under
  #
  # @param [Veritas::Header] header
  #   the veritas header, or coercible to veritas header
  #
  # @example with coercible header
  #   source = RelationSource::InMemory.new
  #   source.register(:foo, [[:id, String], [:foo, String]]) # => source
  #
  # @example with instace of veritas header
  #   source = RelationSource::InMemory.new
  #   source.register(:foo, Veritas::Heade.coerce([[:id, String], [:foo, String]])) # => source
  #
  # @return [self]
  #
  def register(name, header)
    header = Veritas::Header.coerce(header)
    relation = @map.fetch(name) do
      @map[name]=build(name, header)
    end
    self
  end

  # Relation registry for in memory adapters 
  class InMemory < self

  private

    # Build veritas in memory relation
    #
    # @param [Symbol] name
    #   the relation name
    #
    # @param [Veritas::Relation::Header] header
    #
    # @return [Veritas::Relation]
    # 
    # @api private
    #
    def build(_name, header)
      Veritas::Relation.new(header, [])
    end

  end

  # Relation registry backed by base relations in adapters
  class Adapter

    # Initialize object
    #
    # @param [Veritas::Adapter] adapter
    #
    # @return [undefined]
    #
    # @api private
    #
    def initialize(adapter)
      @adapter = adapter
      super()
    end

  private

    # Build veritas gateway relation
    #
    # @param [Symbol] name
    #   the relatio name
    #
    # @param [Veritas::Relation::Header] header
    #
    # @return [Veritas::Adapter::Gateway]
    #
    # @api private
    #
    def build(name, header)
      relation = Veritas::Relation::Base.new(name, header)
      @adapter.gateway(relation)
    end

  end
end