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mongodb - 使用索引查询 Mongo 数组

问题描述

有人可以解释这种行为吗？

db.inventory.insertMany( [
   { item: "journal", instock: [ { warehouse: "A", qty: null }, { warehouse: "C", qty: 15 } ] },
   { item: "notebook", instock: [ { warehouse: "C", qty: 5 } ] },
   { item: "paper", instock: [ { warehouse: "A", qty: 60 }, { warehouse: "B", qty: 15 } ] },
   { item: "planner", instock: [ { warehouse: "A", qty: 40 }, { warehouse: "B", qty: 5 } ] },
   { item: "postcard", instock: [ { warehouse: "B", qty: 15 }, { warehouse: "C", qty: 35 } ] }
]);

复制自https://docs.mongodb.com/v4.2/tutorial/query-array-of-documents/

但第一项instock.0.qty被替换为null.

因此，这个查询会产生奇怪的结果：

> db.inventory.find({"instock.0.qty": null})
{ "_id" : ObjectId("6194329212c7421dbaaeac81"), "item" : "journal", "instock" : [ { "warehouse" : "A", "qty" : null }, { "warehouse" : "C", "qty" : 15 } ] }
{ "_id" : ObjectId("6194329212c7421dbaaeac82"), "item" : "notebook", "instock" : [ { "warehouse" : "C", "qty" : 5 } ] }
{ "_id" : ObjectId("6194329212c7421dbaaeac83"), "item" : "paper", "instock" : [ { "warehouse" : "A", "qty" : 60 }, { "warehouse" : "B", "qty" : 15 } ] }
{ "_id" : ObjectId("6194329212c7421dbaaeac84"), "item" : "planner", "instock" : [ { "warehouse" : "A", "qty" : 40 }, { "warehouse" : "B", "qty" : 5 } ] }
{ "_id" : ObjectId("6194329212c7421dbaaeac85"), "item" : "postcard", "instock" : [ { "warehouse" : "B", "qty" : 15 }, { "warehouse" : "C", "qty" : 35 } ] }

编辑：我只期待一个结果，但他们都回来了。

标签： mongodbmongodb-query

解决方案

此 Jira 票证中报告了一个类似问题：Incorrect filter result when using an null match inside an indexed array field。

提议的建议$type用于检查为空的值。

db.collection.find({
  "instock.0.qty": {
    $type: "null"
  }
})

示例 Mongo Playground

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