mongodb + nodejs查找并返回文档中的特定字段

Question

I'm trying to extract specific document fields from a mongodb collection (v 3.0.8 at MongoLab). The returned documents must fall within a date range. My goal is to extract specific fields from these documents. My nodejs code,

var query = {}, operator1 = {}, operator2 = {}, operator3 = {} ;

operator1.$gte = +startDate;
operator2.$lte = +endDate;
operator3.$ne  = 'move';

query['xid'] = 1; // Problem here?
query['date']  = Object.assign(operator1, operator2);
query['type']  = operator3;

console.log(query);

MongoClient.connect(connection, function(err, db) {

    if(err){ 
        res.send(err); 
    } else {
        db.collection('jbone')
          .find(query)
          .toArray(function(err, result){
              console.log(err);
            res.json(result);
            });
    };
});

If I opt to return all fields in the date range, the query works fine. If I select only field xid I get no results. My query object looks sensible according to the docs . console.log(err) gives:

    { xid: 1,
      date: { '$gte': 20160101, '$lte': 20160107 },
      type: { '$ne': 'move' } }
   null

null is the err .

Can anyone help me understand what I'm doing wrong?

Or point me to another similar SO questions with an answer?

Thanks

Answer 1

To select the specific field could be done as below

.find( 
  {date: { '$gte': 20160101, '$lte': 20160107 }, type: { '$ne': 'move' }},
  { xid: 1} )

Sample codes as following.

   query['date']  = Object.assign(operator1, operator2);
   query['type']  = operator3;
    db.collection('jbone')
      .find(query, {xid: 1})
      .toArray(function(err, result){
          console.log(err);
        res.json(result);
        });