MongoDB Kafka 连接器未生成具有 Mongo 文档 ID 的消息密钥

Question

I'm using the beta release of the MongoDB Kafka Connector to publish from MongoDB to a Kafka topic.

Messages are generated into Kafka but their key is null when it should be the document id:

This is my connect standalone config :

bootstrap.servers=xxx:9092

# The converters specify the format of data in Kafka and how to translate it into Connect data. Every Connect user will
# need to configure these based on the format they want their data in when loaded from or stored into Kafka
key.converter=org.apache.kafka.connect.json.JsonConverter
value.converter=org.apache.kafka.connect.json.JsonConverter
# Converter-specific settings can be passed in by prefixing the Converter's setting with the converter you want to apply
# it to
key.converter.schemas.enable=false
value.converter.schemas.enable=false

# The internal converter used for offsets and config data is configurable and must be specified, but most users will
# always want to use the built-in default. Offset and config data is never visible outside of Kafka Connect in this format.
internal.key.converter=org.apache.kafka.connect.json.JsonConverter
internal.value.converter=org.apache.kafka.connect.json.JsonConverter
internal.key.converter.schemas.enable=false
internal.value.converter.schemas.enable=false

And the mongodb source properties :

name=mongo-source
connector.class=com.mongodb.kafka.connect.MongoSourceConnector
tasks.max=1

# Connection and source configuration
connection.uri=mongodb+srv://xxx
database=mydb
collection=mycollection

topic.prefix=someprefix
poll.max.batch.size=1000
poll.await.time.ms=5000

# Change stream options
pipeline=[]
batch.size=0
change.stream.full.document=updateLookup
collation=

Below there's an example of a message String value:

"{\"_id\": {\"_data\": \"xxx\"}, \"operationType\": \"replace\", \"clusterTime\": {\"$timestamp\": {\"t\": 1564140389, \"i\": 1}}, \"fullDocument\": {\"_id\": \"5\", \"name\": \"Some Client\", \"clientId\": \"someclient\", \"clientSecret\": \"1234\", \"whiteListedIps\": [], \"enabled\": true, \"_class\": \"myproject.Client\"}, \"ns\": {\"db\": \"mydb\", \"coll\": \"mycollection\"}, \"documentKey\": {\"_id\": \"5\"}}"

I tried using a transform to extract if from the value, specifically from the documentKey field:

transforms=InsertKey
transforms.InsertKey.type=org.apache.kafka.connect.transforms.ValueToKey
transforms.InsertKey.fields=documentKey

But got an exception:

Caused by: org.apache.kafka.connect.errors.DataException: Only Struct objects supported for [copying fields from value to key], found: java.lang.String
    at org.apache.kafka.connect.transforms.util.Requirements.requireStruct(Requirements.java:52)
    at org.apache.kafka.connect.transforms.ValueToKey.applyWithSchema(ValueToKey.java:79)
    at org.apache.kafka.connect.transforms.ValueToKey.apply(ValueToKey.java:65)

Any ideas to generate a key with the document id?

Answer 1

According to exception, that is thrown:

Caused by: org.apache.kafka.connect.errors.DataException: Only Struct objects supported for [copying fields from value to key], found: java.lang.String
    at org.apache.kafka.connect.transforms.util.Requirements.requireStruct(Requirements.java:52)
    at org.apache.kafka.connect.transforms.ValueToKey.applyWithSchema(ValueToKey.java:79)
    at org.apache.kafka.connect.transforms.ValueToKey.apply(ValueToKey.java:65)

Unfortunately Mongo DB connector , that you use, it doesn't create properly schema .

Above connector create Record with key and value schema's as String . Check this line:: How record is created by connector . That is the reason why you can't apply Transformation to it

Answer 2

这应该在 1.3.0 版中得到支持： https : //jira.mongodb.org/browse/KAFKA-40