Mongo DB查询-如果条件在C ++代码中实现，则聚合$ cond

Question

I have a mongo DB query as below

db.getCollection('ABC_COLLECTION_01').aggregate ([{ "$group" : { "_id" : 0, "total" : { "$sum" : "$columA" }, "total_sub" : { "$sum" : {$cond:{ if: { $gte: [ "$columnB", new ISODate("2018-01-01T04:58:09.000+0100") ] }, then: "$columA", else: 0 }}} }}])

This query is working fine. If I run this on ABC_COLLECTION_01, it will return result like (just for an example)

total = 250 & total_sub = 120

Now I have to write this query in C++ code using mongo::BSONArrayBuilder as below

//Calculate 2 sum
aBuilder.append(BSON("$group"<<BSON("_id"<<0
                                        <<"total"<<BSON("$sum"<<'$' +columA)
                                        <<"total_sub"<<BSON("$sum"<<'$cond'<<'if'<<'$' +columB<<"$gte"<<rmsmongo::utils::Adaptor::ToMongoDate(StartTime,true)<<'then'<<'$' +columA<<'else'<<0))));
mongo::BSONArray New_AggregationQuery = aBuilder.arr();
std::auto_ptr<dsclient::Cursor> Cursor = _MyCollection.aggregate(New_AggregationQuery, dsclient::Option_aggregate().retry(dsclient::Retry(dsclient::ExponentialRetry, 2)).maxTimeMS(200000));

If you see the $cond I have written for $total_sub is wrong in C++ code- it is not working. Can you please help me to get it corrected? Thanks in advance

Answer 1

Please note that the legacy C++ driver which you appear to be using here is end-of-life. I cannot recommend strongly enough that you immediately switch to the new mongocxx driver, found on the master branch of the same repo. It offers significant advantages, not the least of which is that it is actively maintained.

That said, if you look closely, you can see that the if expression in your working query has a subdocument, but in your C++ code, you aren't starting a new BSON subdocument. There are probably other errors.

Seriously though, I really recommend you stop working on this and get migrated to the new driver. Any bugs or non-conformances in the legacy driver (or are you even using 26compat) will never be fixed.