Get back BulkWriteError from the Mongo shell - mongodb

Question

I want to store writeErrors documents into another collection in MongoDB while performing a bulk.execute(). I am basically doing a bulk insert/update but want to capture all the errors into another collection in parallel to the bulk operation.
I can see the BulkWriteError object is returned in Mongo-Shell, I can also see the writeErrors array in the object. But how can I capture it?

Answer 1

In accordance with https://github.com/mongodb/mongo/blob/master/src/mongo/shell/bulk_api.js (line 363):
// Bulk errors are basically bulk results with additional error information
BulkWriteResult.apply(this, arguments);
So you can use the BulkWriteResult.getWriteErrors() method.
try {
bulk.execute();
...
} catch(err) {
if ("name" in err && err.name == 'BulkWriteError') {
var wErrors = err.getWriteErrors();
wErrors.forEach(function(doc){
db.errlog.insert(doc);
});
}
}

Answer 2

I can see the BulkWriteError object is returned in Mongo-Shell
It is not returned. This is a raised exception. You need a try...catch block to get it back:
> bulk = db.w.initializeUnorderedBulkOp();
> bulk.insert({_id:1})
> bulk.insert({_id:1})
> try { result = bulk.execute() } catch(e) { err = e }
> err
BulkWriteError({
"writeErrors" : [
{
"index" : 1,
"code" : 11000,
"errmsg" : "E11000 duplicate key error index: test.w.$_id_ dup key: { : 1.0 }",
"op" : {
"_id" : 1
}
}
],
"writeConcernErrors" : [ ],
"nInserted" : 1,
"nUpserted" : 0,
"nMatched" : 0,
"nModified" : 0,
"nRemoved" : 0,
"upserted" : [ ]
})
Surprisingly enough, it is rather painful to store the BulkWriteError in a collection. One easy way of doing (not necessary an elegant way, though) is to parse the JSON representation of the error to get back the field(s) that interest you.
> db.errlog.insert(JSON.parse(err.tojson()).writeErrors)
// ^^^^^^^^^^^^^^^^^^^^^^^^
// parse the JSON representation of `BulkWriteError`
That way, you get back the array of write errors, that insert will happily store in the collection:
> db.errlog.find().pretty()
{
"_id" : ObjectId("55619737c0c8238aef6e21c5"),
"index" : 0,
"code" : 11000,
"errmsg" : "E11000 duplicate key error index: test.w.$_id_ dup key: { : 1.0 }",
"op" : {
"_id" : 1
}
}