MongoDB Insert key with '$' (dollar)

Question

I am trying to insert a collection with a json object containing a key which starts with \'$\' (for instance: \'$count\'). I read the mongodb v3.0

Answer 1

Field names cannot contain dots (i.e. .) or null characters, and they must not start with a dollar sign (i.e. $).

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In some cases, you may wish to build a BSON object with a user-provided key. In these situations, keys will need to substitute the reserved $ and . characters. Any character is sufficient, but consider using the Unicode full width equivalents: U+FF04 (i.e. “＄”) and U+FF0E (i.e. “．”).

Is not recomanded but you can try this:

dollar = "\uFF04";
＄
dot = "\uFF0E"
．

db.test.save({[dollar]:dot})
WriteResult({ "nInserted" : 1 })
db.test.save({[dot]:dollar})
WriteResult({ "nInserted" : 1 })

db.test.find()
{ "_id" : ObjectId("58256b0f9934a5d1c696c456"), "＄" : "．" }
{ "_id" : ObjectId("58256d359934a5d1c696c457"), "．" : "＄" }