如何在 mongodb 聚合中查找数组内部？ [复制]

Question

我对如何使用 mongodb 聚合在数组内部进行查找有疑问。

例如，我有一个这样的用户数据 json：

{
   "_id": "1234",
   "name": "Tony",
   "language": [
       {
           "_id": "111",
           "language_id": "919",
           "level": "Expert"
       }
       {
           "_id": "111",
           "language_id": "920",
           "level": "Basic"
       }
   ]
} 

还有我的语言集：

{
   "_id": "919",
   "name": "English"
},
{
   "_id": "920",
   "name": "Chinese"
}

我想进行 mongodb 聚合，结果如下：

{
   "_id": "1234",
   "name": "Tony",
   "language": [
       {
           "name": "English",
           "level": "Expert"
       }
       {
           "name": "Chinese",
           "level": "Basic"
       }
   ]
} 

之前谢谢。

Answer 1

• $unwind解构language数组
• $lookup 有语言集合
• $arrayElemAt 从语言返回结果中选择特定索引元素
• $group by _id 并重构 language 数组

db.user.aggregate([
  { $unwind: "$language" },
  {
    $lookup: {
      from: "language",
      localField: "language.language_id",
      foreignField: "_id",
      as: "language.name"
    }
  },
  {
    $group: {
      _id: "$_id",
      name: { $first: "$name" },
      language: {
        $push: {
          name: { $arrayElemAt: ["$language.name.name", 0] },
          level: "$language.level"
        }
      }
    }
  }
])

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