Hi, Pushed new changes under my PR: https://github.com/apache/kafka/pull/6592 <https://github.com/apache/kafka/pull/6592>
Feel free to put any comments in there. Best, Daniyar Yeralin > On Jul 15, 2019, at 1:06 PM, Development <d...@yeralin.net> wrote: > > Hi John, > > I knew I was missing something. Yes, that makes sense now, I removed all > `listSerde()` methods, and left empty constructors instead. > > As per `CommonClientConfigs` I looked at the class, it doesn’t have any > properties related to serdes, and that bothers me a little. > > All properties like `default.key.serde` `default.windowed.key.serde.*` are > located in StreamsConfig. I don’t want to create a confusion. > What also doesn’t make sense to me is that `WindowedSerdes` and its > (de)serializers are not located in org.apache.kafka.common.serialization. I > guess it kind of makes sense since windowed serdes are only available for > kafka streams, not vice versa. > > If everyone is okay to put list properties in `CommonClientConfigs` class, > I’ll go ahead and do that then. > > Thank you for your input! > > Best, > Daniyar Yeralin > >> On Jul 15, 2019, at 11:45 AM, John Roesler <j...@confluent.io> wrote: >> >> Hi all, >> >> Regarding the placement, you might as well move the constants to >> `org.apache.kafka.clients.CommonClientConfigs`, so that the constants and >> the configs and the code are in the same module. >> >> Regarding the constructor... What Matthias said is correct: The serde, >> serializer, and deserializer all need to have zero-arg constructors so they >> can be instantiated reflectively by Kafka. However, the factory method you >> proposed "New method public static <T> Serde<List<T>> ListSerde()" is not a >> constructor, and is not required. It would be used purely from the Java >> interface, but has the drawbacks I listed above. This method, not the >> constructor, is what I proposed to remove from the KIP. >> >> Thanks, >> -John >> >> >> On Mon, Jul 15, 2019 at 10:15 AM Development <d...@yeralin.net >> <mailto:d...@yeralin.net>> wrote: >> One problem though. >> >> Since WindowedSerde (Windowed(De)Serializer) are so similar, I’m trying to >> mimic the implementation of my ListSerde accordingly. >> >> I created couple constants under StreamsConfig: >> >> >> >> And trying to do similar construct: >> final String propertyName = isKey ? >> StreamsConfig.DEFAULT_LIST_KEY_SERDE_INNER_CLASS : >> StreamsConfig.DEFAULT_LIST_VALUE_SERDE_INNER_CLASS; >> But then found out that StreamsConfig is not accessible from >> org.apache.kafka.common.serialization package while window serde >> (de)serializers are located under org.apache.kafka.streams.kstream package. >> >> What should I do? Should I move my classes under >> org.apache.kafka.streams.kstream package instead? >> >>> On Jul 15, 2019, at 10:45 AM, Development <d...@yeralin.net >>> <mailto:d...@yeralin.net>> wrote: >>> >>> Hi Matthias, >>> >>> Thank you for your input. >>> >>> I updated the KIP, made it a little more readable. >>> >>> I think the configuration parameters strategy is finalized then. >>> >>> Do you have any other questions/concerns regarding this KIP? >>> >>> Meanwhile I’ll start doing appropriate code changes, and commit them under >>> my PR. >>> >>> Best, >>> Daniyar Yeralin >>> >>>> On Jul 11, 2019, at 2:44 PM, Matthias J. Sax <matth...@confluent.io >>>> <mailto:matth...@confluent.io>> wrote: >>>> >>>> Daniyar, >>>> >>>> thanks for the update to the KIP. It's in really good shape and well >>>> written. >>>> >>>> About the default constructor question: >>>> >>>> All Serdes/Serializer/Deserializer classes need a default constructor to >>>> create them easily via reflections when specifies in a config. I >>>> understand that it is not super user friendly, but all existing code >>>> works this way. Hence, it seems best to stick with the established pattern. >>>> >>>> We have a similar issue with `TimeWindowedSerde` and >>>> `SessionWindowedSerde`, and I just recently did a PR to improve user >>>> experience that address the exact issue John raised. (cf >>>> https://github.com/apache/kafka/pull/7067 >>>> <https://github.com/apache/kafka/pull/7067>) >>>> >>>> Note, that if a user would instantiate the Serde manually, the user >>>> would also need to call `configure()` to setup the inner serdes. Kafka >>>> Streams would not setup those automatically and one might most likely >>>> end-up with an NPE. >>>> >>>> >>>> Coming back the KIP, and the parameter names. `WindowedSerdes` are >>>> similar to `ListSerde` as they wrap another Serde. For `WindowedSerdes`, >>>> we use the following parameter names: >>>> >>>> - default.windowed.key.serde.inner >>>> - default.windowed.value.serde.inner >>>> >>>> >>>> It might be good to align the naming pattern. I would also suggest to >>>> use `type` instead of `impl`? >>>> >>>> >>>> default.key.list.serde.impl -> default.list.key.serde.type >>>> default.value.list.serde.impl -> default.list.value.serde.type >>>> default.key.list.serde.element -> default.list.key.serde.inner >>>> default.value.list.serde.element -> default.list.value.serde.inner >>>> >>>> >>>> >>>> -Matthias >>>> >>>> >>>> On 7/10/19 8:52 AM, Development wrote: >>>>> Hi John, >>>>> >>>>> Yes, I do agree. That totally makes sense. The only thing is that it goes >>>>> against what Matthias suggested earlier: >>>>> "I think that ... `ListSerde` should have an default constructor and it >>>>> should be possible to pass in the `Class listClass` information via a >>>>> configuration. Otherwise, KafkaStreams cannot use it as default serde.” >>>>> >>>>> What do you think about that? I hope I’m not confusing anything. >>>>> >>>>> Best, >>>>> Daniyar Yeralin >>>>> >>>>>> On Jul 9, 2019, at 5:56 PM, John Roesler <j...@confluent.io >>>>>> <mailto:j...@confluent.io>> wrote: >>>>>> >>>>>> Ah, my apologies, I must have just overlooked it. Thanks for the update, >>>>>> too. >>>>>> >>>>>> Just one more super-small question, do we need this variant: >>>>>> >>>>>>> New method public static <T> Serde<List<T>> ListSerde() in >>>>>>> org.apache.kafka.common.serialization.Serdes class (infers list >>>>>>> implementation and inner serde from config file) >>>>>> >>>>>> It seems like this situation implies my config file is already set up >>>>>> for the list serde, so passing this serde (e.g., in Produced) would have >>>>>> the same effect as not specifying it. >>>>>> >>>>>> I guess that it could be the case that you have the >>>>>> `default.key/value.serde` set to something else, like StringSerde, but >>>>>> you still have the `default.key/value.list.serde.impl/element` set. This >>>>>> seems like it would result in more confusion than convenience, so my gut >>>>>> instinct is maybe we shouldn't introduce the `ListSerde()` variant until >>>>>> people actually request it later on. >>>>>> >>>>>> Thus, we'd just stick with fully config-driven or fully >>>>>> source-code-driven, not half/half. >>>>>> >>>>>> What do you think? >>>>>> >>>>>> Thanks, >>>>>> -John >>>>>> >>>>>> >>>>>> On Tue, Jul 9, 2019 at 9:58 AM Development <d...@yeralin.net >>>>>> <mailto:d...@yeralin.net> <mailto:d...@yeralin.net >>>>>> <mailto:d...@yeralin.net>>> wrote: >>>>>>> >>>>>>> Hi John, >>>>>>> >>>>>>> I hope everyone had a great long weekend. >>>>>>> >>>>>>> Regarding Java interfaces, I may not understand you correctly, but I >>>>>>> think I already listed them: >>>>>>> >>>>>>> So for Produced, you would use it in the following fashion, for >>>>>>> example: Produced.keySerde(Serdes.ListSerde(ArrayList.class, >>>>>>> Serdes.Integer())) >>>>>>> >>>>>>> I also updated the KIP, and added a section “Serialization Strategy” >>>>>>> where I describe our logic of conditional serialization based on the >>>>>>> type of an inner serde. >>>>>>> >>>>>>> Thank you! >>>>>>> >>>>>>> Best, >>>>>>> Daniyar Yeralin >>>>>>> >>>>>>> On Jun 26, 2019, at 11:44 AM, John Roesler <j...@confluent.io >>>>>>> <mailto:j...@confluent.io> <mailto:j...@confluent.io >>>>>>> <mailto:j...@confluent.io>>> wrote: >>>>>>> >>>>>>> Thanks for the update, Daniyar! >>>>>>> >>>>>>> In addition to specifying the config interface, can you also specify >>>>>>> the Java interface? Namely, if I need to pass an instance of this >>>>>>> serde in to the DSL directly, as in Produced, Materialized, etc., what >>>>>>> constructor(s) would I have available? Likewise with the Serializer >>>>>>> and Deserailizer. I don't think you need to specify the implementation >>>>>>> logic, since we've already discussed it here. >>>>>>> >>>>>>> If you also want to specify the serialized format of the data records >>>>>>> in the KIP, it could be useful documentation, as well as letting us >>>>>>> verify the schema for forward/backward compatibility concerns, etc. >>>>>>> >>>>>>> Thanks, >>>>>>> John >>>>>>> >>>>>>> On Wed, Jun 26, 2019 at 10:33 AM Development <d...@yeralin.net >>>>>>> <mailto:d...@yeralin.net> <mailto:d...@yeralin.net >>>>>>> <mailto:d...@yeralin.net>>> wrote: >>>>>>> >>>>>>> >>>>>>> Hey, >>>>>>> >>>>>>> Finally made updates to the KIP: >>>>>>> https://cwiki.apache.org/confluence/display/KAFKA/KIP-466%3A+Add+support+for+List%3CT%3E+serialization+and+deserialization >>>>>>> >>>>>>> <https://cwiki.apache.org/confluence/display/KAFKA/KIP-466%3A+Add+support+for+List%3CT%3E+serialization+and+deserialization> >>>>>>> >>>>>>> <https://cwiki.apache.org/confluence/display/KAFKA/KIP-466%3A+Add+support+for+List%3CT%3E+serialization+and+deserialization >>>>>>> >>>>>>> <https://cwiki.apache.org/confluence/display/KAFKA/KIP-466%3A+Add+support+for+List%3CT%3E+serialization+and+deserialization>> >>>>>>> >>>>>>> <https://cwiki.apache.org/confluence/display/KAFKA/KIP-466:+Add+support+for+List%3CT%3E+serialization+and+deserialization >>>>>>> >>>>>>> <https://cwiki.apache.org/confluence/display/KAFKA/KIP-466:+Add+support+for+List%3CT%3E+serialization+and+deserialization> >>>>>>> >>>>>>> <https://cwiki.apache.org/confluence/display/KAFKA/KIP-466:+Add+support+for+List%3CT%3E+serialization+and+deserialization >>>>>>> >>>>>>> <https://cwiki.apache.org/confluence/display/KAFKA/KIP-466:+Add+support+for+List%3CT%3E+serialization+and+deserialization>>> >>>>>>> Sorry for the delay :) >>>>>>> >>>>>>> Thank You! >>>>>>> >>>>>>> Best, >>>>>>> Daniyar Yeralin >>>>>>> >>>>>>> On Jun 22, 2019, at 12:49 AM, Matthias J. Sax <matth...@confluent.io >>>>>>> <mailto:matth...@confluent.io> <mailto:matth...@confluent.io >>>>>>> <mailto:matth...@confluent.io>>> wrote: >>>>>>> >>>>>>> Yes, something like this. I did not think about good configuration >>>>>>> parameter names yet. I am also not sure if I understand all proposed >>>>>>> configs atm. But all configs should be listed and explained in the KIP >>>>>>> anyway, and we can discuss further after you have updated the KIP (I can >>>>>>> ask more detailed question if I have any). >>>>>>> >>>>>>> >>>>>>> -Matthias >>>>>>> >>>>>>> On 6/21/19 2:05 PM, Development wrote: >>>>>>> >>>>>>> Yes, you are right. ByteSerializer is not what I need to have in a list >>>>>>> of primitives. >>>>>>> >>>>>>> As for the default constructor and configurability, just want to make >>>>>>> sure. Is this what you have on your mind? >>>>>>> >>>>>>> Best, >>>>>>> Daniyar Yeralin >>>>>>> >>>>>>> >>>>>>> >>>>>>> On Jun 21, 2019, at 2:51 PM, Matthias J. Sax <matth...@confluent.io >>>>>>> <mailto:matth...@confluent.io> <mailto:matth...@confluent.io >>>>>>> <mailto:matth...@confluent.io>> >>>>>>> <mailto:matth...@confluent.io <mailto:matth...@confluent.io> >>>>>>> <mailto:matth...@confluent.io <mailto:matth...@confluent.io>>>> wrote: >>>>>>> >>>>>>> Thanks for the update! >>>>>>> >>>>>>> I think that `ListDeserializer`, `ListSerializer`, and `ListSerde` >>>>>>> should have an default constructor and it should be possible to pass in >>>>>>> the `Class listClass` information via a configuration. Otherwise, >>>>>>> KafkaStreams cannot use it as default serde. >>>>>>> >>>>>>> >>>>>>> For the primitive serializers: `BytesSerializer` is not primitive IMHO, >>>>>>> as is it for `byte[]` with variable length -- it's for arrays, not for >>>>>>> single `byte` (note, that `Bytes` is a Kafka class wrapping `byte[]`). >>>>>>> >>>>>>> >>>>>>> For tests, we can comment on the PR. No need to do this in the KIP >>>>>>> discussion. >>>>>>> >>>>>>> >>>>>>> Can you also update the KIP? >>>>>>> >>>>>>> >>>>>>> >>>>>>> -Matthias >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> On 6/21/19 11:29 AM, Development wrote: >>>>>>> >>>>>>> I made and pushed necessary commits, so we could review the final >>>>>>> version under PR https://github.com/apache/kafka/pull/6592 >>>>>>> <https://github.com/apache/kafka/pull/6592> >>>>>>> <https://github.com/apache/kafka/pull/6592 >>>>>>> <https://github.com/apache/kafka/pull/6592>> >>>>>>> >>>>>>> I also need some advice on writing tests for this new serde. So far I >>>>>>> only have two test cases (roundtrip and empty payload), I’m not sure >>>>>>> if it is enough. >>>>>>> >>>>>>> Thank y’all for your help in this KIP :) >>>>>>> >>>>>>> Best, >>>>>>> Daniyar Yeralin >>>>>>> >>>>>>> >>>>>>> On Jun 21, 2019, at 1:44 PM, John Roesler <j...@confluent.io >>>>>>> <mailto:j...@confluent.io> <mailto:j...@confluent.io >>>>>>> <mailto:j...@confluent.io>> >>>>>>> <mailto:j...@confluent.io <mailto:j...@confluent.io> >>>>>>> <mailto:j...@confluent.io <mailto:j...@confluent.io>>>> wrote: >>>>>>> >>>>>>> Hey Daniyar, >>>>>>> >>>>>>> Looks good to me! Thanks for considering it. >>>>>>> >>>>>>> Thanks, >>>>>>> -John >>>>>>> >>>>>>> On Fri, Jun 21, 2019 at 9:04 AM Development <d...@yeralin.net >>>>>>> <mailto:d...@yeralin.net> <mailto:d...@yeralin.net >>>>>>> <mailto:d...@yeralin.net>> >>>>>>> <mailto:d...@yeralin.net <mailto:d...@yeralin.net> >>>>>>> <mailto:d...@yeralin.net <mailto:d...@yeralin.net>>> >>>>>>> <mailto:d...@yeralin.net <mailto:d...@yeralin.net> >>>>>>> <mailto:d...@yeralin.net <mailto:d...@yeralin.net>>>> wrote: >>>>>>> Hey John and Matthias, >>>>>>> >>>>>>> Yes, now I see it all. I’m storing lots of redundant information. >>>>>>> Here is my final idea. Yes, now a user should pass a list type. I >>>>>>> realized that’s the type is not really needed in ListSerializer, but >>>>>>> only in ListDeserializer: >>>>>>> >>>>>>> >>>>>>> In ListSerializer we will start storing sizes only if serializer is >>>>>>> not a primitive serializer: >>>>>>> >>>>>>> >>>>>>> Then, in deserializer, we persist passed list type, so that during >>>>>>> deserialization we could create an instance of it with predefined >>>>>>> listSize for better performance. >>>>>>> We also try to locate a primitiveSize based on passed deserializer. >>>>>>> If it is not there, then primitiveSize will be null. Which means >>>>>>> that each entry’s size was encoded individually. >>>>>>> >>>>>>> >>>>>>> This looks much cleaner and more concise. >>>>>>> >>>>>>> What do you think? >>>>>>> >>>>>>> Best, >>>>>>> Daniyar Yeralin >>>>>>> >>>>>>> On Jun 20, 2019, at 5:45 PM, Matthias J. Sax <matth...@confluent.io >>>>>>> <mailto:matth...@confluent.io> <mailto:matth...@confluent.io >>>>>>> <mailto:matth...@confluent.io>> >>>>>>> <mailto:matth...@confluent.io <mailto:matth...@confluent.io> >>>>>>> <mailto:matth...@confluent.io <mailto:matth...@confluent.io>>> >>>>>>> <mailto:matth...@confluent.io <mailto:matth...@confluent.io> >>>>>>> <mailto:matth...@confluent.io <mailto:matth...@confluent.io>>>> wrote: >>>>>>> >>>>>>> For encoding the list-type: I see John's point about re-encoding the >>>>>>> list-type redundantly. However, I also don't like the idea that the >>>>>>> Deserializer returns a fixed type... >>>>>>> >>>>>>> Maybe it's best allow users to specify the target list type on >>>>>>> deserialization via config? >>>>>>> >>>>>>> Similar for the primitive types: I don't think we need to encode the >>>>>>> type size, but users could specify the type on the deserializer (via a >>>>>>> config again)? >>>>>>> >>>>>>> >>>>>>> About generics: nesting could be arbitrarily deep. Hence, I doubt >>>>>>> we can >>>>>>> support this and a cast will be necessary at some point in the user >>>>>>> code. >>>>>>> >>>>>>> >>>>>>> >>>>>>> -Matthias >>>>>>> >>>>>>> >>>>>>> >>>>>>> On 6/20/19 1:21 PM, John Roesler wrote: >>>>>>> >>>>>>> Hey Daniyar, >>>>>>> >>>>>>> Thanks for looking at it! >>>>>>> >>>>>>> Something like your screenshot is more along the lines of what I was >>>>>>> thinking. Sorry, but I didn't follow what you mean, how would that not >>>>>>> be "vanilla java"? >>>>>>> >>>>>>> Unfortunately the deserializer needs more information, though. For >>>>>>> example, what if the inner type is a Map<String,String>? The serde >>>>>>> could >>>>>>> only be used to produce a LinkedList<Map>, thus, we'd still need an >>>>>>> inner serde, like you have in the KIP (Serde<T> innerSerde). >>>>>>> >>>>>>> Something more like Serde<LinkedList<MyRecord>> = Serdes.listSerde( >>>>>>> /**list type**/ LinkedList.class, >>>>>>> /**inner serde**/ new MyRecordSerde() >>>>>>> ) >>>>>>> >>>>>>> And in configuration, it's something like: >>>>>>> default.key.serde: org...ListSerde >>>>>>> default.key.list.serde.type: java.util.LinkedList >>>>>>> default.key.list.serde.inner: com.mycompany.MyRecordSerde >>>>>>> >>>>>>> >>>>>>> What do you think? >>>>>>> Thanks, >>>>>>> -John >>>>>>> >>>>>>> On Thu, Jun 20, 2019 at 2:46 PM Development <d...@yeralin.net >>>>>>> <mailto:d...@yeralin.net> <mailto:d...@yeralin.net >>>>>>> <mailto:d...@yeralin.net>> >>>>>>> <mailto:d...@yeralin.net <mailto:d...@yeralin.net> >>>>>>> <mailto:d...@yeralin.net <mailto:d...@yeralin.net>>> >>>>>>> <mailto:d...@yeralin.net <mailto:d...@yeralin.net> >>>>>>> <mailto:d...@yeralin.net <mailto:d...@yeralin.net>>> >>>>>>> <mailto:d...@yeralin.net <mailto:d...@yeralin.net> >>>>>>> <mailto:d...@yeralin.net <mailto:d...@yeralin.net>> >>>>>>> <mailto:d...@yeralin.net <mailto:d...@yeralin.net> >>>>>>> <mailto:d...@yeralin.net <mailto:d...@yeralin.net>>>>> wrote: >>>>>>> >>>>>>> Hey John, >>>>>>> >>>>>>> I gave read about TypeReference. It could work for the list serde. >>>>>>> However, it is not directly >>>>>>> supported: >>>>>>> https://github.com/FasterXML/jackson-databind/issues/1490 >>>>>>> <https://github.com/FasterXML/jackson-databind/issues/1490> >>>>>>> <https://github.com/FasterXML/jackson-databind/issues/1490 >>>>>>> <https://github.com/FasterXML/jackson-databind/issues/1490>> >>>>>>> <https://github.com/FasterXML/jackson-databind/issues/1490 >>>>>>> <https://github.com/FasterXML/jackson-databind/issues/1490> >>>>>>> <https://github.com/FasterXML/jackson-databind/issues/1490 >>>>>>> <https://github.com/FasterXML/jackson-databind/issues/1490>>> >>>>>>> The only way is to pass an actual class object into the constructor, >>>>>>> something like: >>>>>>> >>>>>>> It could be an option, but not a pretty one. What do you think of my >>>>>>> approach to use vanilla java and canonical class name? (As described >>>>>>> previously) >>>>>>> >>>>>>> Best, >>>>>>> Daniyar Yeralin >>>>>>> >>>>>>> On Jun 20, 2019, at 2:45 PM, Development <d...@yeralin.net >>>>>>> <mailto:d...@yeralin.net> <mailto:d...@yeralin.net >>>>>>> <mailto:d...@yeralin.net>> >>>>>>> <mailto:d...@yeralin.net <mailto:d...@yeralin.net> >>>>>>> <mailto:d...@yeralin.net <mailto:d...@yeralin.net>>> >>>>>>> <mailto:d...@yeralin.net <mailto:d...@yeralin.net> >>>>>>> <mailto:d...@yeralin.net <mailto:d...@yeralin.net>>> >>>>>>> <mailto:d...@yeralin.net <mailto:d...@yeralin.net> >>>>>>> <mailto:d...@yeralin.net <mailto:d...@yeralin.net>> >>>>>>> <mailto:d...@yeralin.net <mailto:d...@yeralin.net> >>>>>>> <mailto:d...@yeralin.net <mailto:d...@yeralin.net>>>>> wrote: >>>>>>> >>>>>>> Hi John, >>>>>>> >>>>>>> Thank you for your input! Yes, my idea looks a little bit over >>>>>>> engineered :) >>>>>>> >>>>>>> I also wanted to see a feedback from Mathias as well since he gave >>>>>>> me an idea about storing fixed/variable size entries. >>>>>>> >>>>>>> Best, >>>>>>> Daniyar Yeralin >>>>>>> >>>>>>> On Jun 18, 2019, at 6:06 PM, John Roesler <j...@confluent.io >>>>>>> <mailto:j...@confluent.io> <mailto:j...@confluent.io >>>>>>> <mailto:j...@confluent.io>> >>>>>>> <mailto:j...@confluent.io <mailto:j...@confluent.io> >>>>>>> <mailto:j...@confluent.io <mailto:j...@confluent.io>>> >>>>>>> <mailto:j...@confluent.io <mailto:j...@confluent.io> >>>>>>> <mailto:j...@confluent.io <mailto:j...@confluent.io>>> >>>>>>> <mailto:j...@confluent.io <mailto:j...@confluent.io> >>>>>>> <mailto:j...@confluent.io <mailto:j...@confluent.io>> >>>>>>> <mailto:j...@confluent.io <mailto:j...@confluent.io> >>>>>>> <mailto:j...@confluent.io <mailto:j...@confluent.io>>>>> wrote: >>>>>>> >>>>>>> Hi Daniyar, >>>>>>> >>>>>>> That's a very clever solution! >>>>>>> >>>>>>> One observation is that, now, this is what we might call a >>>>>>> polymorphic >>>>>>> serde. That is, you're detecting the actual concrete type and then >>>>>>> promising to produce the exact same concrete type on read. >>>>>>> There are >>>>>>> some inherent problems with this approach, which in general >>>>>>> require >>>>>>> some kind of schema registry (not necessarily Schema >>>>>>> Registry, just >>>>>>> any registry for schemas) to solve. >>>>>>> >>>>>>> Notice that every serialized record has quite a bit of duplicated >>>>>>> information: the concrete type as well as a byte to indicate >>>>>>> whether >>>>>>> the value type is a fixed size, and, if so, an integer to >>>>>>> indicate the >>>>>>> actual size. These constitute a schema, of sorts, because they >>>>>>> tell us >>>>>>> later how exactly to deserialize the data. Unfortunately, this >>>>>>> information is completely redundant. In all likelihood, the >>>>>>> information will be exactly the same for every record in the >>>>>>> topic. >>>>>>> This problem is essentially the core motivation for serializations >>>>>>> like Avro: to move the schema outside of the serialization >>>>>>> itself, so >>>>>>> that the records won't contain so much redundant information. >>>>>>> >>>>>>> In this light, I'm wondering if it makes sense to go back to >>>>>>> something >>>>>>> like what you had earlier in which you don't support perfectly >>>>>>> preserving the concrete type for _this_ serde, but instead just >>>>>>> support deserializing to _some_ List. Then, you could defer full, >>>>>>> perfect, type preservation to serdes that have an external >>>>>>> system in >>>>>>> which to register their type information. >>>>>>> >>>>>>> There does exist an alternative, if we really do want to >>>>>>> preserve the >>>>>>> concrete type (which does seem kind of nice). You can add a >>>>>>> configuration option specifically for the serde to configure >>>>>>> what the >>>>>>> list type will be, and maybe what the element type is, as well. >>>>>>> >>>>>>> As far as "related work" goes, you might be interested to take >>>>>>> a look >>>>>>> at how Jackson can be configured to deserialize into a specific, >>>>>>> arbitrarily nested, generically parameterized class structure. >>>>>>> Specifically, you might find >>>>>>> https://fasterxml.github.io/jackson-core/javadoc/2.0.0/com/fasterxml/jackson/core/type/TypeReference.html >>>>>>> >>>>>>> <https://fasterxml.github.io/jackson-core/javadoc/2.0.0/com/fasterxml/jackson/core/type/TypeReference.html> >>>>>>> >>>>>>> <https://fasterxml.github.io/jackson-core/javadoc/2.0.0/com/fasterxml/jackson/core/type/TypeReference.html >>>>>>> >>>>>>> <https://fasterxml.github.io/jackson-core/javadoc/2.0.0/com/fasterxml/jackson/core/type/TypeReference.html>> >>>>>>> <https://fasterxml.github.io/jackson-core/javadoc/2.0.0/com/fasterxml/jackson/core/type/TypeReference.html >>>>>>> >>>>>>> <https://fasterxml.github.io/jackson-core/javadoc/2.0.0/com/fasterxml/jackson/core/type/TypeReference.html> >>>>>>> >>>>>>> <https://fasterxml.github.io/jackson-core/javadoc/2.0.0/com/fasterxml/jackson/core/type/TypeReference.html >>>>>>> >>>>>>> <https://fasterxml.github.io/jackson-core/javadoc/2.0.0/com/fasterxml/jackson/core/type/TypeReference.html>>> >>>>>>> interesting. >>>>>>> >>>>>>> Thanks, >>>>>>> -John >>>>>>> >>>>>>> On Mon, Jun 17, 2019 at 12:38 PM Development <d...@yeralin.net >>>>>>> <mailto:d...@yeralin.net> <mailto:d...@yeralin.net >>>>>>> <mailto:d...@yeralin.net>> >>>>>>> <mailto:d...@yeralin.net <mailto:d...@yeralin.net> >>>>>>> <mailto:d...@yeralin.net <mailto:d...@yeralin.net>>> >>>>>>> <mailto:d...@yeralin.net <mailto:d...@yeralin.net> >>>>>>> <mailto:d...@yeralin.net <mailto:d...@yeralin.net>>> >>>>>>> <mailto:d...@yeralin.net <mailto:d...@yeralin.net> >>>>>>> <mailto:d...@yeralin.net <mailto:d...@yeralin.net>> >>>>>>> <mailto:d...@yeralin.net <mailto:d...@yeralin.net> >>>>>>> <mailto:d...@yeralin.net <mailto:d...@yeralin.net>>>>> wrote: >>>>>>> >>>>>>> >>>>>>> bump >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>> >>>>> >>>> >>> >> >
