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https://issues.apache.org/jira/browse/KAFKA-8369?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16886379#comment-16886379
]
Jason Gustafson commented on KAFKA-8369:
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[~Yohan123] Good question. My thought was that the key would be the field that
is identified with the "mapKey" property in the schema definition. For example,
take the following schema:
{code:java}
{
"apiKey": 24,
"type": "request",
"name": "AddPartitionsToTxnRequest",
// Version 1 is the same as version 0.
"validVersions": "0-1",
"fields": [
{ "name": "TransactionalId", "type": "string", "versions": "0+",
"entityType": "transactionalId",
"about": "The transactional id corresponding to the transaction."},
{ "name": "ProducerId", "type": "int64", "versions": "0+", "entityType":
"producerId",
"about": "Current producer id in use by the transactional id." },
{ "name": "ProducerEpoch", "type": "int16", "versions": "0+",
"about": "Current epoch associated with the producer id." },
{ "name": "Topics", "type": "[]AddPartitionsToTxnTopic", "versions": "0+",
"about": "The partitions to add to the transation.", "fields": [
{ "name": "Name", "type": "string", "versions": "0+", "mapKey": true,
"entityType": "topicName",
"about": "The name of the topic." },
{ "name": "Partitions", "type": "[]int32", "versions": "0+",
"about": "The partition indexes to add to the transaction" }
]}
]
}{code}
In the topics array, the map key is the topic name. So what I was hoping to be
able to get out of this would be something like `Map<String, List<Integer>>` or
maybe `Map<String, AddPartitionsToTxnTopic>`. Does that make sense?
> Generate an immutable Map view for generated messages with a map key
> --------------------------------------------------------------------
>
> Key: KAFKA-8369
> URL: https://issues.apache.org/jira/browse/KAFKA-8369
> Project: Kafka
> Issue Type: Improvement
> Reporter: Jason Gustafson
> Priority: Major
>
> When using the "mapKey" feature, we get an ImplicitLinkedHashCollection which
> can be used like a map using the `find()` API. The benefit of this is
> hopefully avoiding a conversion to another type when handled by the broker,
> but it is a little cumbersome to work with, so we often end up doing the
> conversion anyway. One improvement would be to provide a way to convert this
> collection to an immutable Map view so that it is easier to work with
> directly.
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