MongoDB Kafka Connector无法使用Mongo文档ID生成消息密钥

Question

我正在使用MongoDB Kafka Connector to publish from MongoDB to a Kafka topic.的beta版本

消息已生成到Kafka中，但当其键应为文档ID时，它们的键为空：

这是我的连接独立配置：

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

以及 mongodb源属性：

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=

下面有一个消息字符串值的示例：

"{\"_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\"}}"

我尝试使用转换从值（尤其是从documentKey字段）中提取if：

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

但是有一个例外：

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)

有什么想法可以生成带有文档ID的密钥吗？

Answer 1

根据异常抛出：

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)

很遗憾，您使用的Mongo DB connector不会创建正确的模式。

在上述连接器上，创建键和值模式为String的Record。 检查以下行：How record is created by connector。这就是为什么您不能对其应用转换的原因

Answer 2

在1.3.0版中应该支持： https://jira.mongodb.org/browse/KAFKA-40