Javascript 有没有办法从mongodb中检索数据作为键值映射，其中键是字段的值（使用Mongoose）

我的Mongodb收藏中有以下数据：

{_id: xxx1, fieldA: valueA_1, fieldB: valueB_1, fieldC: valueC_1},
{_id: xxx2, fieldA: valueA_1, fieldB: valueB_2, fieldC: valueC_2},
{_id: xxx3, fieldA: valueA_2, fieldB: valueB_3, fieldC: valueC_3},

是否有Mongodb聚合运算符或类似运算符返回此类结构：

{
 "valueA_1": [
              {_id: xxx1, fieldA: valueA_1, fieldB: valueB_1, fieldC: valueC_1},
              {_id: xxx2, fieldA: valueA_1, fieldB: valueB_2, fieldC: valueC_2}
             ],

 "valueA_2": [
              {_id: xxx3, fieldA: valueA_2, fieldB: valueB_3, fieldC: valueC_3}
             ]
}

现在我正在做一个简单的Schema.find，然后对结果应用reduce函数：

    data.reduce(function (map, obj) {
      map[obj.fieldA] = map[obj.fieldA] ? [...map[obj.fieldA], obj] : [obj];
      return map;
    }, {});

我想知道如何仅使用mongodb\mongoose操作符完成此行为 还有，如果使用它们而不是reduce函数，性能是否会更好

谢谢大家!

试试这个

db.collection.aggregate([
  {
    $group: { // first group by the required fieldA
      _id: "$fieldA",
      docs: {
        $push: "$$ROOT"
      }
    }
  },
  {
    $group: { // this group to gather all documents in one array 'allDocsInOneArray' of objects
      // each object has a key = the value of fieldA, and a value = an array of the docs belong to this fieldA
      _id: null,
      allDocsInOneArray: {
        $push: {
          k: "$_id", // the key of the object (should be the value of fieldA, which is the _id now after the first group stage)
          v: "$docs" // an array of docs belong to this fieldA
          // the object should be in this format { k: '', v: [] } in order to be able to convert the whole array to another object in $arrayToObject operation
        }
      }
    }
  },
  {
    "$replaceRoot": {
      "newRoot": {
        "$arrayToObject": "$allDocsInOneArray"  // convert the array of objects to object with key = k (fieldA), value = v (its docs)
      }
    }
  }
])

你可以

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希望能有所帮助

嗨，穆罕默德！看起来很完美。你能给我讲讲表演吗？哪种策略应该更好？我认为，如果您可以直接从db获得所需形状的数据，这将比使用JavaScript更好