tenancy_middleware.rb

# Could perhaps live in app/lib, or app/middleware?
class TenancyMiddleware < ThinkingSphinx::Middlewares::Middleware
  def call(contexts)
    contexts.each do |context|
      Inner.new(context).call
    end

    app.call contexts
  end
  
  class Inner
    def initialize(context)
      @context = context
    end
    
    def call
      tenant = options[:tenant]
      return unless tenant
      
      classes = options[:classes] || []
      indices = options[:indices] || []
      
      set = ThinkingSphinx::IndexSet.new(classes, indices)
      options[:classes] = []
      options[:indices] = set.select { |index|
        index.name[/_#{tenant.id}_(core|delta)$/]
      }
    end
    
    private
    
    def options
      @context.search.options
    end
  end
end

# Put this line in an initializer:
ThinkingSphinx::Middlewares::DEFAULT.insert(0, TenancyMiddleware)

Hi Pat,

Correction:
instead of

options[:indices] = set.select { |index|
        index.name[/_#{tenant.id}_(core|delta)$/]
}

there should be

options[:indices] = set.select { |index|
        index.name[/_#{tenant.id}_(core|delta)$/]
}.map(&:name)