mongcxx and get_timestamp

[Jeff Abrahamson]

I'm having a bit of trouble with timestamps in mongocxx.  (I know that object creation time is encoded in the oid.)

I have an object that looks like this in the mongo shell:

...
"server_time" : ISODate("2016-11-17T21:47:07.141Z"),
...

and in C++ when I say

LOG_INFO << bsoncxx::to_json(doc);

I see this (newlines added here for readability):

{ "_id" : { "$oid" : "..." },
  ...,
  "server_time" : { "$date" : 1479419227141 }
}

So I try

doc["server_time"].get_timestamp().timestamp

and get an exception, "expected element type k_timestamp".  So maybe it just looks like a timestamp but isn't.  No worries, I'll try this:

doc["server_time"]["$date"].get_int64().value / 1000

and now I throw with message "unset document::element".

Can anyone point me to what mongocxx is hoping for here?

Thanks.

-- 

Jeff Abrahamson
+33 6 24 40 01 57
+44 7920 594 255

http://p27.eu/jeff/

[Andrew Morrow]

Hi Jeff -

Yeah, I can see how that would be confusing. What I recommend doing here is printing the actual type of the server_time field. I think you will find that it is actually of type date, rather than timestamp. Try extracting it as doc["server_time"].get_date() and see if things work better. I suspect that the $date in the JSON output isn't real - it is simply how the underlying C driver's JSON support choses to identify the field as a date type.

Thanks,

Andrew

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[Jeff Abrahamson]

Ah, yes, that's it.  Thanks, Andrew.

For future readers of this thread, I needed to write this to get seconds since the epoch:

std::chrono::duration_cast<std::chrono::seconds>(
    doc["server_time"].get_date().value
).count()

Jeff Abrahamson

https://www.p27.eu/jeff/