Kafka Connect Transformation: Extract a Long value from json field and insert as key

Question

I have the following json on a topic that the JDBC connector publishes to

{"APP_SETTING_ID":9,"APP_SETTING_NAME":"my_name","SETTING_KEY":"my_setting_key"}

Here's my connector file

name=data.app_setting
connector.class=io.confluent.connect.jdbc.JdbcSourceConnector
poll.interval.ms=500
tasks.max=4
mode=timestamp
query=SELECT APP_SETTING_ID, APP_SETTING_NAME, SETTING_KEY,FROM MY_TABLE with (nolock)
timestamp.column.name=LAST_MOD_DATE
topic.prefix=data.app_setting

key.converter=org.apache.kafka.connect.json.JsonConverter
key.converter.schemas.enable=false
value.converter=org.apache.kafka.connect.json.JsonConverter
value.converter.schemas.enable=false

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

This does add a key but its also a json format like

{"APP_SETTING_ID":9}

While I just want 9 to be the key instead of the map. In the database it's stored as a Long value.

Answer 1

ValueToKey takes a list of fields within the value, and returns a mapping of those fields to their values.

I think you need a second transform to extract only a single one of those fields.

transforms=ReplaceKey,ExtractKey

# Replaces the key with fields in the value. Creates a map for all listed fields
transforms.ReplaceKey.type=org.apache.kafka.connect.transforms.ValueToKey
transforms.ReplaceKey.fields=APP_SETTING_ID

# Extracts a specfic field from the key, assuming it's a map/struct type
transforms.ExtractKey.type=org.apache.kafka.connect.transforms.ExtractField$Key
transforms.ExtractKey.field=APP_SETTING_ID