MongoDB-用子文档更新/替换数组字段以嵌入其内容

Question

db.events.insertMany([{
    "_id" : ObjectId("5f6c5b0594911c0b7231643d"),
    "title" : "Test Event",
    "tags" : [ 
        "5fd8cef2368c625a9d7516cb"
    ]
},
{
    "_id" : ObjectId("5fb3896afc13ae2ed1000000"),
    "title" : "Test Event 2",
    "tags" : [ 
        "5fd8cef2368c625a9d7516cb", 
        "5fd8cfb04a4a6063ab4ca4bf", 
        "5fd8cfb04a4a6063ab4ca4c0"
    ]
}
]);

db.tags.insertMany([{
    "_id" : ObjectId("5fd8cef2368c625a9d7516cb"),
    "name" : "Foo",
    "createdAt" : ISODate("2020-12-15T14:57:54.096Z")
},
{
    "_id" : ObjectId("5fd8cfb04a4a6063ab4ca4bf"),
    "name" : "Bar",
    "createdBy" : "[e-mail]",
    "createdAt" : ISODate("2020-12-16T14:57:54.096Z")
},
{
    "_id" : ObjectId("5fd8cfb04a4a6063ab4ca4c0"),
    "name" : "Foobar",
    "createdAt" : ISODate("2020-12-17T14:57:54.096Z")
}
]);

{
    "_id" : ObjectId("5f6c5b0594911c0b7231643d"),
    "title" : "Test Event",
    "tags" : [{
        "_id" : ObjectId("5fd8cef2368c625a9d7516cb"),
        "name" : "Foo",
        "createdAt" : ISODate("2020-12-15T14:57:54.096Z")
    }]
},
{
    "_id" : ObjectId("5fb3896afc13ae2ed1000000"),
    "title" : "Test Event 2",
    "tags" : [{
        "_id" : ObjectId("5fd8cef2368c625a9d7516cb"),
        "name" : "Foo"
    },
    {
        "_id" : ObjectId("5fd8cfb04a4a6063ab4ca4bf"),
        "name" : "Bar"
    },
    {
        "_id" : ObjectId("5fd8cfb04a4a6063ab4ca4c0"),
        "name" : "Foobar"
    }]
}

婴儿步

我尝试使用聚合管道，并在最后一步中通过匹配和查找它们的内容来替换。我不太熟悉通过聚合管道解决这个问题。

db.getCollection('events').aggregate([
    { $match: { tags: { "$exists" : true } } },
    {
       $lookup:
         {
           from: "tags",
           localField: "tags",
           foreignField: "_id",
           as: "taags"
         }
    },
    ])

Answer 1

您可以使用$toobjectid运算符在$lookup阶段之前将标记的id从string转换为objectId,

• $addfields添加新字段并更新/格式化现有字段
• $map循环迭代标记数组
• $toobjectid将字符串objectId转换为objectId类型
• 将名称标记放在中，作为$lookup阶段
的属性

  // $match stage here
  {
    $addFields: {
      tags: {
        $map: {
          input: "$tags",
          in: { $toObjectId: "$$this" }
        }
      }
    }
  },
  {
    $lookup: {
      from: "tags",
      localField: "tags",
      foreignField: "_id",
      as: "tags"
    }
  }

操场

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  { $out: "updated_events" }

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