如何正确查找 mongodb 中的多个字段？

Question

假设我有 2 个 collections

// Post collection:
{
    "_id": "61f7a933b209737de4cc2657",
    "author": "61d30188cf93e83e08d14112",
    "title": "Some title",
    "createts": 1643620659355
}

// User collection:

{
    "_id": "61d30188cf93e83e08d14112",
    "nickname": "Bob",
    "link": "bobspage"
}

我需要得到这个结果

{
    "_id": "61f7a933b209737de4cc2657",
    "author": {
        "_id": "61d30188cf93e83e08d14112",
        "nickname": "Bob",
        "link": "bobspage"
    },
    "title": "Some title",
    "createts": 1643620659355
}

我如何使用聚合发出请求，这将显示此输出？

Answer 1

只需在聚合查询中使用$lookup：

首先 $lookup，它生成一个名为 author 的字段，它是一个包含所有值的数组。
要获取 author 作为对象，请使用 $arrayElemAt.

db.post.aggregate([
  {
    "$lookup": {
      "from": "user",
      "localField": "author",
      "foreignField": "_id",
      "as": "author"
    }
  },
  {
    "$addFields": {
      "author": {
        "$arrayElemAt": [
          "$author",
          0
        ]
      }
    }
  }
])

示例here

如何正确查找 mongodb 中的多个字段？

How to properly lookup for several fields in mongodb?

mongodb

aggregation-framework