Mongodb 使用合并对象而不覆盖子文档

我正在尝试合并聚合管道中的两个字段

我想改变这一点：

{
   "a": 1,
   "b": {
      "first": {
          "property_a": "some_value",
          "property_b": "some_value",
          "property_c": "some_value"
      },
      "second": {
          "property_a": "some_value",
          "property_b": "some_value",
          "property_c": "some_value"
      },
      "third": {
          "property_a": "some_value",
          "property_b": "some_value",
          "property_c": "some_value"
      },
      "fiftieth": {
          "property_a": "some_value",
          "property_b": "some_value",
          "property_c": "some_value"
      }
   },
   "c": {
      "first": {
          "property_x": "some_value",
          "property_y": "some_value"
      },
      "second": {
          "property_x": "some_value",
          "property_y": "some_value"
      },
      "fiftieth": {
          "property_x": "some_value",
          "property_y": "some_value"
      }
   }
}

在这种情况下，无需指定“b”下列出的每个键：

在

mergeObjects

的文档中，它指出：

合并对象在合并文档时覆盖字段值。如果要合并的文档包含相同的字段名，则结果文档中的字段具有上次合并文档中的值

---

如何在不指定每个键的情况下合并字段b和c的子文档（在我的实际用例中有85个键）。此外，字段c可能没有在b下列出所有键。或者这是不可能的

您可以使用

$objectToArray

将对象转换为k、v对，组合并

$unwind

它们，

$group

按键名并合并文档，然后

$group

按_-id将键收集回一起

db.collection.aggregate([
  {$addFields: {
      combined: {
        $concatArrays: [
          {$objectToArray: "$b"},
          {$objectToArray: "$c"}
        ]
      }
  }},
  {$unwind: "$combined"},
  {$group: {
      _id: {_id: "$_id", key: "$combined.k"},
      doc: {$first: "$$ROOT"},
      v: {$mergeObjects: "$combined.v"}
  }},
  {$group: {
      _id: "$_id._id",
      doc: {$first: "$doc"},
      combined: {$push: {
          k: "$_id.key",
          v: "$v"
      }}
  }},
  {$addFields: {"doc.b": {$arrayToObject: "$combined"}}},
  {$project: {
    combined: 0,
    "doc.c": 0
  }},
  {$replaceRoot: {newRoot: "$doc"}}
])

---

是否确定

b

或

c

中的任何字段都不会包含文档以外的内容？是的。字段b和c仅包含文档。此解决方案有效。我真的很感谢你的帮助！非常感谢你！

db.collection.aggregate([
  {$addFields: {
      combined: {
        $concatArrays: [
          {$objectToArray: "$b"},
          {$objectToArray: "$c"}
        ]
      }
  }},
  {$unwind: "$combined"},
  {$group: {
      _id: {_id: "$_id", key: "$combined.k"},
      doc: {$first: "$$ROOT"},
      v: {$mergeObjects: "$combined.v"}
  }},
  {$group: {
      _id: "$_id._id",
      doc: {$first: "$doc"},
      combined: {$push: {
          k: "$_id.key",
          v: "$v"
      }}
  }},
  {$addFields: {"doc.b": {$arrayToObject: "$combined"}}},
  {$project: {
    combined: 0,
    "doc.c": 0
  }},
  {$replaceRoot: {newRoot: "$doc"}}
])