如何在mongoDB中从两个不同的模型中找到两个字段？

db.users.aggregate([
   {
      $lookup:
         {
           from: "orders",      // 指定关联的集合
           localField: "_id",   // 当前集合中的字段
           foreignField: "userId", // 关联集合中的字段
           as: "userOrders"     // 将关联结果保存到userOrders字段中
         }
   }
])

db.users.aggregate([
   {
      $lookup:
         {
           from: "orders",
           localField: "_id",
           foreignField: "userId",
           as: "userOrders"
         }
   },
   {
      $project:
         {
           "_id": 1,
           "name": 1,
           "userOrders.field1": 1,
           "userOrders.field2": 1
         }
   }
])

db.users.aggregate([
   {
      $match: { "name": "John" }
   },
   {
      $lookup:
         {
           from: "orders",
           localField: "_id",
           foreignField: "userId",
           as: "userOrders"
         }
   }
])