MongoDB聚合错误$ in需要一个数组

Question

下面是我的文档，我想过滤所有这些邮政编码以及它们对应的res_count，它们也存在于名为data的数组中。

文档：

{ "data" : [ "10451", "10458", "10467", "10461", "10462" ] }
{ "zipcode" : "10470", "res_count" : 8 }
{ "zipcode" : "10454", "res_count" : 10 }
{ "zipcode" : "10466", "res_count" : 11 }
{ "zipcode" : "10455", "res_count" : 9 }
{ "zipcode" : "10462", "res_count" : 29 }
{ "zipcode" : "10461", "res_count" : 25 }
{ "zipcode" : "10467", "res_count" : 15 }
{ "zipcode" : "10465", "res_count" : 28 }
{ "zipcode" : "10452", "res_count" : 11 }
{ "zipcode" : "10469", "res_count" : 10 }
{ "zipcode" : "10459", "res_count" : 7 }
{ "zipcode" : "10457", "res_count" : 14 }
{ "zipcode" : "10451", "res_count" : 68 }
{ "zipcode" : "10463", "res_count" : 28 }
{ "zipcode" : "10458", "res_count" : 34 }
{ "zipcode" : "10468", "res_count" : 12 }
{ "zipcode" : "10475", "res_count" : 14 }
{ "zipcode" : "10474", "res_count" : 10 }
{ "zipcode" : "10473", "res_count" : 3 }

我尝试使用$in，但它说"errmsg" : "$in needs an array"

Answer 1

尝试一下：

  db.find(
       { zipcode: { $in: [ "10451", "10458", "10467", "10461", "10462" ] } }
    )

Answer 2

因为您仅在一个文档中具有data字段。因此，如果在$in中运行$match，例如{$match : {$in : ['$zipcode', '$data']}}，则会抛出相同的错误"errmsg" : "$in needs an array"。

但是为什么？

[通常，Aggregation pipeline stages对收集文档执行原子操作，因此每个文档都不能使用，因此不能使用一个文档的字段取代其他文档。 （<< [Ex：-如果尝试$addFields添加从$data提取的新字段'dataCopy'-addFields不会向文档中不存在'data'字段的任何新字段添加）。因此，为了执行此操作，您需要使用$group将集合中的所有文档带到一个文档中，请尝试下面的聚合查询：

db.collection.aggregate([
  /** Iterate on all docs & push document which has 'data' field into 'dataDoc' &
   * push all other docs into 'allDocs' array field
   */
  {
    $group: {
      _id: "",
      dataDoc: {
        $push: {
          $cond: [{ $eq: [{ $type: "$data" }, "array"] }, "$$ROOT", "$$REMOVE"]
        }
      },
      allDocs: {
        $push: {
          $cond: [
            { $eq: [{ $type: "$zipcode" }, "string"] },
            "$$ROOT",
            "$$REMOVE"
          ]
        }
      }
    }
  },
  /** Unwind dataDoc array to make it 'dataDoc' field of type object */
  {
    $unwind: "$dataDoc"
  },
  /** Re-create 'allDocs' array field with objects which meet required condition,
   * newly formed array will have docs whose zipcode exists in data array
   * */
  {
    $addFields: {
      allDocs: {
        $filter: {
          input: "$allDocs",
          cond: { $in: ["$$this.zipcode", "$dataDoc.data"] }
        }
      }
    }
  },
  /** Unwind 'allDocs' array */
  {
    $unwind: "$allDocs"
  },
  /** Make 'allDocs' object field as new root, after this your result will have docs
   * whose zipcode exists in data array
   */
  {
    $replaceRoot: {
      newRoot: "$allDocs"
    }
  }
]);

Test：

MongoDB-Playground