使用$unset的mongodb聚合丢弃子字段

假设我有这样的文档，我想使用

$unset

操作符删除

info.$time

字段

{
“id”：1234，
“信息”：{
“msg”：“你好，世界”，
“$time”：时间戳（1610515499）
}
}

我试过了

db.aggregate([
  { $unset: [ "info.$time" ] },
  // next stage
])

但这是错误的

"errmsg" : "Invalid $project :: caused by :: FieldPath
field names may not start with '$'."

---

我还尝试了

“info.time”

，但实际上并没有删除该字段。

如注释中所述，以$开头的字段不受支持

如果您使用的是驱动程序而不是MongoDB shell，则在尝试插入此类数据时应收到一个错误：

irb（main）：006:0>a['foo']。插入一个（{foo:{'$bar'=>1}）
回溯（最近一次呼叫最后一次）：
16:from/home/w/.rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/mongo-2.14.0/lib/mongo/operation/shared/sessions_受支持。rb:226:in'tap'
15:from/home/w/.rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/mongo-2.14.0/lib/mongo/operation/shared/sessions_-supported.rb:231:in“block in-in-build_消息”
14:from/home/w/.rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/mongo-2.14.0/lib/mongo/protocol/msg.rb:152:在“序列化”中
13:from/home/w/.rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/mongo-2.14.0/lib/mongo/protocol/message.rb:192:in“serialize”
12:from/home/w/.rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/mongo-2.14.0/lib/mongo/protocol/message.rb:331:在“序列化”字段中
11:from/home/w/.rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/mongo-2.14.0/lib/mongo/protocol/message.rb:331:in'each'
10:from/home/w/.rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/mongo-2.14.0/lib/mongo/protocol/message.rb:343:in`block in serialize_字段'
9:from/home/w/.rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/mongo-2.14.0/lib/mongo/protocol/serializers.rb:187:in“serialize”
8:from/home/w/.rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/mongo-2.14.0/lib/mongo/protocol/serializers.rb:187:in'each'
7:from/home/w/.rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/mongo-2.14.0/lib/mongo/protocol/serializers.rb:194:in`block in serialize'
6:from/home/w/.rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/mongo-2.14.0/lib/mongo/protocol/serializers.rb:316:in“serialize”
5:from/home/w/.rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/mongo-2.14.0/lib/mongo/protocol/serializers.rb:316:in'each'
4:from/home/w/.rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/mongo-2.14.0/lib/mongo/protocol/serializers.rb:317:in`block in serialize'
3:from/home/w/.rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/mongo-2.14.0/lib/mongo/protocol/serializers.rb:358:in“serialize”
2:from/home/w/.rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/bson-4.11.1/lib/bson/hash.rb:42:in“to_bson”
1:from/home/w/.rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/bson-4.11.1/lib/bson/hash.rb:42:in'put_hash'
BSON:：String:：IllegalKey（“$bar”在MongoDB中是非法密钥。密钥不能以“$”开头或包含“.”。）

是否要从集合中永久删除该字段？或者只需要从结果中删除？请参阅。将字段名以美元

$

符号开头是一个非常糟糕的主意，尽管这可能是可行的。