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$unsetField（表达式操作符）

定义

$unsetField

版本 5.0 中的新增功能。

删除文档中的指定字段。

You can use $unsetField to remove fields with names that contain periods (.) or that start with dollar signs ($).

$unsetField is an alias for $setField using $$REMOVE to remove fields.

语法

$unsetField 通过以下语法实现：

{
   $unsetField: {
      field: <String>,
      input: <Object>,
   }
}

您必须提供以下字段：

字段	类型	说明
`field`	字符串	要删除的 `input`对象中的字段。 `field`可以是解析为字符串常量的任何有效表达式。
`input`	对象	包含要删除的 `field` 的文档。 `input` 必须解析为对象、`missing`、`null` 或 `undefined`。

行为

If input evaluates to missing, undefined, or null, $unsetField returns null and does not update input.
If input evaluates to anything other than an object, missing, undefined, or null, $unsetField returns an error.
If field resolves to anything other than a string constant, $unsetField returns an error.
$unsetField doesn't implicitly traverse objects or arrays. For example, $unsetField evaluates a field value of "a.b.c" as a top-level field "a.b.c" instead of as a nested field, { "a": { "b": { "c": } } }.

示例

删除包含句点 (`.`) 的字段

以库存集合为例：

db.inventory.insertMany( [
   { _id: 1, item: "sweatshirt", qty: 300, "price.usd": 45.99 },
   { _id: 2, item: "winter coat", qty: 200, "price.usd": 499.99 },
   { _id: 3, item: "sun dress", qty: 250, "price.usd": 199.99 },
   { _id: 4, item: "leather boots", qty: 300, "price.usd": 249.99 },
   { _id: 5, item: "bow tie", qty: 180, "price.usd": 9.99 }
 ] )

Use the $replaceWith pipeline stage and the $unsetField operator to remove the "price.usd" field from each document:

db.inventory.aggregate( [
   { $replaceWith: {
        $unsetField: {
           field: "price.usd",
           input: "$$ROOT"
   } } }
 ] )

操作返回以下结果：

[
  { _id: 1, item: 'sweatshirt', qty: 300 },
  { _id: 2, item: 'winter coat', qty: 200 },
  { _id: 3, item: 'sun dress', qty: 250 },
  { _id: 4, item: 'leather boots', qty: 300 },
  { _id: 5, item: 'bow tie', qty: 180 }
]

删除以美元符号 (`$`) 开头的字段

以库存集合为例：

db.inventory.insertMany( [
   { _id: 1, item: "sweatshirt", qty: 300, "$price": 45.99 },
   { _id: 2, item: "winter coat", qty: 200, "$price": 499.99 },
   { _id: 3, item: "sun dress", qty: 250, "$price": 199.99 },
   { _id: 4, item: "leather boots", qty: 300, "$price": 249.99 },
   { _id: 5, item: "bow tie", qty: 180, "$price": 9.99 }
 ] )

Use the $replaceWith pipeline stage with the $unsetField and $literal operators to remove the "$price" field from each document:

db.inventory.aggregate( [
   { $replaceWith: {
        $unsetField: {
           field: { $literal: "$price" },
           input: "$$ROOT"
   } } }
] )

操作返回以下结果：

[
  { _id: 1, item: 'sweatshirt', qty: 300 },
  { _id: 2, item: 'winter coat', qty: 200 },
  { _id: 3, item: 'sun dress', qty: 250 },
  { _id: 4, item: 'leather boots', qty: 300 },
  { _id: 5, item: 'bow tie', qty: 180 }
]

删除子字段

以库存集合为例：

db.inventory.insertMany( [
   { _id: 1, item: "sweatshirt", qty: 300, "price": {"usd":45.99, "euro": 38.77 } },
   { _id: 2, item: "winter coat", qty: 200, "price": { "usd": 499.99, "euro": 420.51 } },
   { _id: 3, item: "sun dress", qty: 250, "price": { "usd": 199.99, "euro": 167.70 } },
   { _id: 4, item: "leather boots", qty: 300, "price": { "usd": 249.99, "euro": 210.68 } },
   { _id: 5, item: "bow tie", qty: 180, "price": { "usd": 9.99, "euro": 8.42 } }
 ] )

"price" 字段包含一个具有两个子字段的文档，即 "usd" 和 "euro"。无法使用 "price.euro" 来识别和删除 "euro" ，因为 MongoDB 将 "price.euro"解析为恰好包含句点 (.) 的顶级字段名称。

Use the $replaceWith pipeline stage with $setField and a nested $unsetField operation to remove the "euro" field:

db.inventory.aggregate( [
   { $replaceWith: {
        $setField: {
           field: "price",
           input: "$$ROOT",
           value: {
              $unsetField: {
                 field: "euro",
                 input: { $getField: "price" }
   } } } } }
] )

操作返回以下结果：

[
   { _id: 1, item: "sweatshirt", qty: 300, price: { usd: 45.99 } },
   { _id: 2, item: "winter coat", qty: 200, price: { usd: 499.99 } },
   { _id: 3, item: "sun dress", qty: 250, price: { usd: 199.99 } },
   { _id: 4, item: "leather boots", qty: 300, price: { usd: 249.99 } },
   { _id: 5, item: "bow tie", qty: 180, price: { usd: 9.99 } }
]

了解详情

$unsetField（表达式操作符）

定义

语法

行为

示例

删除包含句点 (.) 的字段

删除以美元符号 ($) 开头的字段

删除子字段

了解详情

删除包含句点 (`.`) 的字段

删除以美元符号 (`$`) 开头的字段