Adding multiple fields to documents in mongodb using pymongo

Question

I have a sample collection of documents in mongo db like below

[{"name":"hans","age":30,"test":"pass","pre":"no","calc":"no"},
{"name":"abs","age":20,"test":"not_pass","pre":"yes","calc":"no"},
{"name":"cdf","age":40,"test":"pass"},
{"name":"cvf","age":30,"test":"not_pass","pre":"no","calc":"yes"},
{"name":"cdf","age":23,"test":"pass"},
{"name":"asd","age":35,"test":"not_pass"}]

For some documents the fields pre and calc are not present. I want to add those two fields to the documents which dont have those fields with value null for both "pre":"null", "calc":"null".

The final document should look like

[{"name":"hans","age":30,"test":"pass","pre":"no","calc":"no"},
{"name":"abs","age":20,"test":"not_pass","pre":"yes","calc":"no"},
{"name":"cdf","age":40,"test":"pass","pre":"null","calc":"null"},
{"name":"cvf","age":30,"test":"not_pass","pre":"no","calc":"yes"},
{"name":"cdf","age":23,"test":"pass","pre":"null","calc":"null"},
{"name":"asd","age":35,"test":"not_pass","pre":"null","calc":"null"}]

I tried this way but didnt work.

db.users.update({}, { "$set" : { "pre":"null","calc":"null" }}, false,true)

Answer 1

The easiest option is to run this query for every missing field that you have , for example for pre:

db.collection.update({
pre: {
    $exists: false
  }
},
{
 "$set": {
   "pre": null
 }
},
{
  multi: true
})

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