slow aggregate mongo query...

aggregate_to_join_and_query.rb

# Order has many order_deliveries

order_deliveries = OrderDelivery.collection.aggregate([
    {
      "$match" => {
        created_at: { '$gte' => Date.new(2017,10,1), '$lt' => Date.new(2017,10,7) },
        delivery_status: { '$in' => ['processing', 'pending', 'arrived'] }
      }
    },
    {
      "$lookup" => {
        from: "orders",
        localField: "order_id",
        foreignField: "_id",
        as: "order_document"
      }      
    },
    {
      "$unwind" => "$order_document"
    },
    {
      "$match" => {
        "order_document.seller_id" => BSON::ObjectId('5951ce1901cda3710a000007')
      }
    }
  ])