mongo DB集合中唯一文档的查询

Question

我需要一个查询，只复制唯一的文件从"A“集合到"B”集合。我将创建"B“集合的索引，然后将唯一的文档从"A”复制到"B“集合。

"A“藏书有近3671945份文件。

"A“集合Mongo DB文件结构：

    {
        "_id" : ObjectId("5d654ed25616a9d461bc0a91"),
        "aC" : "AN",
        "aI" : "ABCD",
        "aN" : "000000000001",
        "aT" : "AB",
        "pD" : "2022-11-07",
        "transaction" : {
            "seqNo" : 1,
            "tC" : "S"
        }
    },
    {
        "_id" : ObjectId("5d654ed25616a9d461bc0a93"),
        "aC" : "AN",
        "aI" : "ABCD",
        "aN" : "000000000001",
        "aT" : "AB",
        "pD" : "2022-11-07",
        "transaction" : {
            "seqNo" : 1,
            "tC" : "S"
        }
    },
    {
        "_id" : ObjectId("5d654ed25616a9d461bc0a92"),
        "aC" : "AN",
        "aI" : "ABCD",
        "aN" : "000000000002",
        "aT" : "AB",
        "pD" : "2022-11-08",
        "transaction" : {
            "seqNo" : 2,
            "tC" : "S"
        }
    }

现在，我将在"B“集合上创建主索引，如下所示，

    {
    "aC" : 1,
    "aI" : 1,
    "aN" : 1,
    "aT" : 1,
    "transaction.seqNo" : 1,
    "transaction.tC" : 1,
    "pD" : 1
    }

请您帮助我查询唯一的文档，从"A“集合到"B”集合，基于"B“集合上启用的索引？

在查询方面需要帮助。

提前谢谢。

Answer 1

使用$group和$first对每个分组选择一个文档。保存$$ROOT，然后用保存的$$ROOT替换。最后使用$merge保存到集合B。

db.collection.aggregate([
  {
    "$group": {
      "_id": {
        "aC": "$aC",
        "aI": "$aI",
        "aN": "$aN",
        "aT": "$aT",
        "seqNo": "$transaction.seqNo",
        "tC": "$transaction.tC",
        "pD": "$pD"
      },
      doc: {
        $first: "$$ROOT"
      }
    }
  },
  {
    "$replaceRoot": {
      "newRoot": "$doc"
    }
  },
  {
    "$merge": {
      "into": "B",
      "on": "_id",
      "whenMatched": "replace"
    }
  }
])

蒙戈

附带注意:您可能希望在创建索引之前执行插入，以提高写入速度。