An example insert command that results in a duplicate key write error:

> db.runCommand({ insert: "temp-metrics-coll", documents: [{"_id" : "sampleId-1521573287000000000"}] })
{
	"n" : 0,
	"writeErrors" : [
		{
			"index" : 0,
			"code" : 11000,
			"errmsg" : "E11000 duplicate key error collection: temp-metrics-db.temp-metrics-coll index: _id_ dup key: { : \"sampleId-1521573287000000000\" }"
		}
	],
	"ok" : 1
}

I'm not sure why the ok field is set to 1 here. I have noticed this before, and I think this has caused issues with mgo in the past, specifically with duplicate key errors.

Maybe this is a mongod bug? But the driver is also not checking for the writeErrors field. The relevant file is mongo/private/conn/protocl.go.