检索 mongodb 集合中所有文档的特定字段

Question

I have a mongodb collection user_col that looks like this;

[{
  'Code': '557921',
  'Serial': 0,
  'UserName': 'morbidMacaw674005',
  '_id': ObjectId('5ee328c32cd209a5f60b56f1')},
 {
  'Code': '127142',
  'Serial': 1,
  'UserName': 'jumpyChough940073',
  '_id': ObjectId('5ee328c32cd209a5f60b56f2')},
 {
  'Code': '739173',
  'Serial': 2,
  'UserName': 'jumpyPretzels824773',
  '_id': ObjectId('5ee328c32cd209a5f60b56f3')},
]

I want to retrieve specific fields of all documents in a mongodb collection into a list of dictionaries. Here is my code;

list(user_col.find({"UserName": 1, "Code": 1}))

However, it returns nothing. What is wrong with my code?

If I run list(user_col.find({})) , all the documents are retrieved. I believe my code is quite close to getting it right.

I am using python 3.7, pymongo. I am also open to using mongoengine.

Answer 1

I will answer my own question.

list(user_col.find({}, {"UserName": 1, "Code": 1}))

The first parameter {} was missing in the code in the question.