kafka connector debezium mongodb CDC update/$set message without filter(_id value)

Question

i am trying to setup syncing from mongodb to kudu with debezium mongodb connector. but as debezium doc tell and also i tried by myself and found, there are no filter(_id value) for debezium mongodb CDC update/$set message.

{
    "after": null,
    "patch": "{\"$v\" : 1,\"$set\" : {\"_upts_ratio_average_points\" : {\"$numberLong\" : \"1564645156749\"},\"updatets\" : {\"$numberLong\" : \"1564645156749\"}}}",
    "source": {
        "version": "0.9.5.Final",
        "connector": "mongodb",
        "name": "promongodbdeb05",
        "rs": "mgset-13056897",
        "ns": "strtest.mg_jsd_result_all",
        "sec": 1564645156,
        "ord": 855,
        "h": -1570214265415439167,
        "initsync": false
    },
    "op": "u",
    "ts_ms": 1564648181536
}

I don't understand why designed like this, without filter really no idea which document is updated. I downloaded the source code of this connector and try to fix it. It looks like class io.debezium.connector.mongodb.transforms.UnwrapFromMongoDbEnvelope is where MongoDB op log message is extracted with code like these. And this file is with confusing both _id and id manipulations and it looks like the committer of the connector indeed tried to include _id value in the CDC update message. I tried to change valueDocument.append("id", keyDocument.get("id")); to valueDocument.append("id", keyDocument.get("_id")); still no _id value in CDC message after the connector is rebuilt and deployed.

Anyone familiar with debezium can help me with this?

{
    private BsonDocument getUpdateDocument(R patchRecord, BsonDocument keyDocument) {
        BsonDocument valueDocument = new BsonDocument();
        BsonDocument document = BsonDocument.parse(patchRecord.value().toString());

        if (document.containsKey("$set")) {
            valueDocument = document.getDocument("$set");
        }

        if (document.containsKey("$unset")) {
            Set<Entry<String, BsonValue>> unsetDocumentEntry = document.getDocument("$unset").entrySet();

            for (Entry<String, BsonValue> valueEntry : unsetDocumentEntry) {
                // In case unset of a key is false we don't have to do anything with it,
                // if it's true we want to set the value to null
                if (!valueEntry.getValue().asBoolean().getValue()) {
                    continue;
                }
                valueDocument.append(valueEntry.getKey(), new BsonNull());
            }
        }

        if (!document.containsKey("$set") && !document.containsKey("$unset")) {
            if (!document.containsKey("_id")) {
                throw new ConnectException("Unable to process Mongo Operation, a '$set' or '$unset' is necessary " +
                        "for partial updates or '_id' is expected for full Document replaces.");
            }
            // In case of a full update we can use the whole Document as it is
            // see https://docs.mongodb.com/manual/reference/method/db.collection.update/#replace-a-document-entirely
            valueDocument = document;
            valueDocument.remove("_id");
        }

        if (!valueDocument.containsKey("id")) {
            valueDocument.append("id", keyDocument.get("id"));
        }

        if (flattenStruct) {
            final BsonDocument newDocument = new BsonDocument();
            valueDocument.forEach((fKey, fValue) -> newDocument.put(fKey.replace(".", delimiter), fValue));
            valueDocument = newDocument;
        }

        return valueDocument;
    }

}

@jiri, thanks a lot for your reply, the message i got always like this:

{ "after": null, "patch": "{\"$v\" : 1,\"$set\" : {\"_upts_ratio_average_points\" : {\"$numberLong\" : \"1564645156749\"},\"updatets\" : {\"$numberLong\" : \"1564645156749\"}}}", "source": { "version": "0.9.5.Final", "connector": "mongodb", "name": "promongodbdeb05", "rs": "mgset-13056897", "ns": "strtest.mg_jsd_result_all", "sec": 1564645156, "ord": 855, "h": -1570214265415439167, "initsync": false }, "op": "u", "ts_ms": 1564648181536 }

and i searched and found someone else can get debezium mongodb CDC like this article: https://rmoff.net/2018/03/27/streaming-data-from-mongodb-into-kafka-with-kafka-connect-and-debezium/ like this: { "after": {\"_id\" : {\"$oid\" : \"58385328e4b001431e4e497a\"}, ....

One can see I can't get _id, so no way for me know this change on which document/record, but as to the above post, it looks like the author can get _id, also by checking code, _id should be there. I used both 0.9.5Final and the 0.7.4 rev which used in the above post. both no luck for me, always without _id value.

Answer 1

when consumer the topic,need to add --property key.print=true.It will have the Key.The value is in the key part.Thanks