Mongodb：使用条件将元素推送到多个嵌套数组中

Question

如何在特定条件下将值推送到多个嵌套数组中？
我有这样的文件

[
  {
    "_id": "class_a",
    "students": [
      {
        "_id": "1a",
        "name": "John",
        "grades": []
      },
      {
        "_id": "1b",
        "name": "Katie",
        "grades": []
      },
      {
        "_id": "1c",
        "name": "Andy",
        "grades": []
      },
      
    ]
  }
]

查询插入嵌套数组。 （不确定这里缺少什么）

db.collection.update({
  "_id": "class_a",
  "students": {
    $elemMatch: {
      "_id": {
        "$in": [
          "1a",
          "1b"
        ]
      }
    }
  }
},
{
  $push: {
    "students.$.grades": "A+"
  }
})

得到以下结果。但我期待John和Katie在grades中都有A+

[
  {
    "_id": "class_a",
    "students": [
      {
        "_id": "1a",
        "grades": ["A+"],
        "name": "John"
      },
      {
        "_id": "1b",
        "grades": [],
        "name": "Katie"
      },
      {
        "_id": "1c",
        "grades": [],
        "name": "Andy"
      }
    ]
  }
]

预期结果

[
  {
    "_id": "class_a",
    "students": [
      {
        "_id": "1a",
        "grades": ["A+"],
        "name": "John"
      },
      {
        "_id": "1b",
        "grades": ["A+"],
        "name": "Katie"
      },
      {
        "_id": "1c",
        "grades": [],
        "name": "Andy"
      }
    ]
  }
]

Mongo playground to test the code

Answer 1

您可以使用 $[<identifier>] 仅更新符合条件的项目。你的第一个{}就是找相关的文件，而 arrayFilters 是寻找相关的项目在文档嵌套数组中：

db.collection.update(
  {_id: "class_a", students: {$elemMatch: {_id: {$in: ["1a", "1b"]}}}},
  {$push: {"students.$[item].grades": "A+"}},
  {arrayFilters: [{"item._id": {$in: ["1a", "1b"]}}], upsert: true}
)

查看它在playground example 上的工作原理

Answer 2

你真的应该为这些使用arrayFilters，否则它只会匹配第一个实体。您根本不需要使用 $elemMatch。

游乐场 - https://mongoplayground.net/p/_7y89KB83Ho

db.collection.update({
  "_id": "class_a"
},
{
  $push: {
    "students.$[students].grades": "A+"
  }
},
{
  "arrayFilters": [
    {
      "students._id": {
        "$in": [
          "1a",
          "1b"
        ]
      }
    }
  ]
})