Thank you all for the discussion!
Here are my comments:
2) I agree we should support Expression as a computed column. But I'm in
favor of Leonard's point that maybe we can also support SQL string
expression as a computed column.
Because it also keeps aligned with DDL. The concern for Expression is that
converting Expression to SQL string, or (de)serializing Expression is
another topic not clear and may involve lots of work.
Maybe we can support Expression later if time permits.
6,7) I still prefer the "new" keyword over builder. I don't think immutable
is a strong reason. I care more about usability and experience from users
and devs perspective.
- Users need to type more words if using builder:
`KafkaConnector.newBuilder()...build()` vs `new KafkaConnector()...`
- It's more difficult for developers to write a descriptor. 2 classes
(KafkaConnector and KafkaConnectorBuilder) + 5 more methods (builders,
schema, partitionedBy, like, etc..).
With the "new" keyword all the common methods are defined by the
framework.
- It's hard to have the same API style for different connectors, because
the common methods are defined by users. For example, some may have
`withSchema`, `partitionKey`, `withLike`, etc...
8) I'm -1 to `ConfigOption`. The ConfigOption is not used on `JsonFormat`,
but the generic `Connector#option`. This doesn't work when using format
options.
new Connector("kafka")
.option(JsonOptions.IGNORE_PARSE_ERRORS, true); // this is wrong,
because "kafka" requires "json.ignore-parse-errors" as the option key, not
the "ignore-parse-errors".
========================================
Hi Timo, regarding having a complete new stack, I have thought about that.
But I still prefer to refactor the existing stack. Reasons:
Because I think it will be more confusing if users will see two similar
stacks and may have many problems if using the wrong class.
For example, we may have two `Schema` and `TableDescriptor` classes. The
`KafkaConnector` can't be used in legacy `connect()` API,
the legacy `Kafka` class can't be used in the new `createTemporaryTable()`
API.
Besides, the existing API has been deprecated in 1.11, I think it's fine to
remove them in 1.12.
Best,
Jark
On Thu, 16 Jul 2020 at 15:26, Jingsong Li <jingsongl...@gmail.com> wrote:
> Thanks for the discussion.
>
> Descriptor lacks the watermark and the computed column is too long.
>
> 1) +1 for just `column(...)`
>
> 2) +1 for being consistent with Table API, the Java Table API should be
> Expression DSL. We don't need pure string support, users should just use
> DDL instead. I think this is just a schema descriptor? The schema
> descriptor should be consistent with DDL, so, definitely, it should
> contain computed columns information.
>
> 3) +1 for not containing Schema#proctime and
> Schema#watermarkFor#boundedOutOfOrderTimestamps, we can just leave them in
> legacy apis.
>
> 6,7) +1 for removing "new" and builder and making it immutable, For Jark,
> the starting method is the static method, the others are not.
>
> 8) +1 for `ConfigOption`, this can be consistent with `WritableConfig`.
> For Leonard, I don't think user needs “json.fail-on-missing-field” rather
> than “fail-on-missing-field”, user should
> need “fail-on-missing-field” rather than “json.fail-on-missing-field", the
> recommended way is "JsonFormat.newInstance().option(....)", should
> configure options in the format scope.
>
> Best,
> Jingsong
>
> On Wed, Jul 15, 2020 at 9:30 PM Leonard Xu <xbjt...@gmail.com> wrote:
>
>> Thanks Jark bring this discussion and organize the FLIP document.
>>
>> Thanks Dawid and Timo for the feedback. Here are my thoughts.
>>
>> 1) I’m +1 with using column() for both cases.
>>
>> 2) Expression DSL vs pure SQL string for computed columns
>>
>> I think we can support them both and implement the pure SQL String first,
>> I agree that Expression DSL brings more possibility and flexibility, but
>> using SQL string is a more unified way which can reuse most logic with DDL
>> like validation and persist in Catalog,
>> and Converting Expression DSL to SQL Expression is another big topic and
>> I did not figure out a feasible idea until now.
>> So, maybe we can postpone the Expression DSL support considered the
>> reality.
>>
>> 3) Methods Schema#proctime and
>> Schema#watermarkFor#boundedOutOfOrderTimestamps
>>
>> +1 with Dawid’s proposal to offer SQL like methods.
>> Schema()
>> .column("proctime", proctime());
>> .watermarkFor("rowtime", $("rowtime").minus(lit(3).seconds()))
>> And we can simplify watermarkFor(“colName”, Expression
>> watermarkStrategy)to watermark(“colName”, Expression watermarkStrategy), I
>> think the later one has can express the meaning of “ WATERMARK FOR
>> column_name AS watermark_strategy_expression“ well.
>>
>> 5)6)7) The new keyword vs the static method vs builder pattern
>>
>> I have not strong tendency, the new keyword and the static method on
>> descriptor can nearly treated as a builder and do same things like
>> builder.
>> For the builder pattern, we will introduce six
>> methods(connector.Builder()、connector.Builder.build(), format.Builder(),
>> format.Builder.build(), Schema.Builder(),Schema.Builder.build() )，I think
>> we could reduce these unnecessary methods. I ‘m slightly +1 for new
>> keyword if we need a choice.
>>
>> 8) `Connector.option(...)` class should also accept `ConfigOption`
>> I’m slightly -1 for this, ConfigOption may not work because the key for
>> format configOption has not format prefix eg： FAIL_ON_MISSING_FIELD of
>> json, we need “json.fail-on-missing-field” rather than
>> “fail-on-missing-field”.
>>
>> public static final ConfigOption<Boolean> FAIL_ON_MISSING_FIELD =
>> ConfigOptions
>> .key("fail-on-missing-field")
>> .booleanType()
>> .defaultValue(false)
>>
>> WDYT?
>>
>> Best,
>> Leonard Xu
>>
>>
>> > 在 2020年7月15日，16:37，Timo Walther <twal...@apache.org> 写道：
>> >
>> > Hi Jark,
>> >
>> > thanks for working on this issue. It is time to fix this last part of
>> inconsistency in the API. I also like the core parts of the FLIP, esp. that
>> TableDescriptor is one entity that can be passed to different methods. Here
>> is some feedback from my side:
>> >
>> > 1) +1 for just `column(...)`
>> >
>> > 2) Expression DSL vs pure SQL string for computed columns
>> > I agree with Dawid. Using the Expression DSL is desireable for a
>> consistent API. Furthermore, otherwise people need to register functions if
>> they want to use them in an expression. Refactoring TableSchema is
>> definitely on the list for 1.12. Maybe we can come up with some
>> intermediate solution where we transform the expression to a SQL expression
>> for the catalog. Until the discussions around FLIP-80 and
>> CatalogTableSchema have been finalized.
>> >
>> > 3) Schema#proctime and Schema#watermarkFor#boundedOutOfOrderTimestamps
>> > We should design the descriptor very close to the SQL syntax. The more
>> similar the syntax the more likely it is too keep the new descriptor API
>> stable.
>> >
>> > 6) static method vs new keyword
>> > Actually, the `new` keyword was one of the things that bothered me most
>> in the old design. Fluent APIs avoid this nowadays.
>> >
>> > 7) make the descriptors immutable with builders
>> > The descriptors are some kind of builders already. But they are not
>> called "builder". Instead of coming up with the new concept of a
>> "descriptor", we should use terminology that people esp. Java/Scala users
>> are familiar with already.
>> >
>> > We could make the descriptors immutable to pass them around easily.
>> >
>> > Btw "Connector" and "Format" should always be in the classname. This
>> was also a mistake in the past. Instead of calling the descriptor just
>> `Kafka` we could call it `KafkaConnector`. An entire example could look
>> like:
>> >
>> > tEnv.createTemporaryTable(
>> > "OrdersInKafka",
>> > KafkaConnector.newBuilder() // builder pattern supported by IDE
>> > .topic("user_logs")
>> > .property("bootstrap.servers", "localhost:9092")
>> > .property("group.id", "test-group")
>> > .format(JsonFormat.newInstance()) // shortcut for no parameters
>> > .schema(
>> > Schema.newBuilder()
>> > .column("user_id", DataTypes.BIGINT())
>> > .column("score", DataTypes.DECIMAL(10, 2))
>> > .column("log_ts", DataTypes.TIMESTAMP(3))
>> > .column("my_ts", toTimestamp($("log_ts"))
>> > .build()
>> > )
>> > .build()
>> > );
>> >
>> > Instead of refacoring the existing classes, we could also think about a
>> completly new stack. I think this would avoid confusion for the old users.
>> We could deprecate the entire `Kafka` class instead of dealing with
>> backwards compatibility.
>> >
>> > 8) minor extensions
>> > A general `Connector.option(...)` class should also accept
>> `ConfigOption` instead of only strings.
>> > A `Schema.column()` should accept `AbstractDataType` that can be
>> resolved to a `DataType` by access to a `DataTypeFactory`.
>> >
>> > What do you think?
>> >
>> > Thanks,
>> > Timo
>> >
>> >
>> > On 09.07.20 18:51, Jark Wu wrote:
>> >> Hi Dawid,
>> >> Thanks for the great feedback! Here are my responses:
>> >> 1) computedColumn(..) vs column(..)
>> >> I'm fine to use `column(..)` in both cases.
>> >> 2) Expression DSL vs pure SQL string for computed columns
>> >> This is a good point. Actually, I also prefer to use Expression DSL
>> because
>> >> this is more Table API style.
>> >> However, this requires to modify TableSchema again to accept & expose
>> >> Expression as computed columns.
>> >> I'm not convinced about this, because AFAIK, we want to have a
>> >> CatalogTableSchema to hold this information
>> >> and don't want to extend TableSchema. Maybe Timo can give some points
>> here.
>> >> Besides, this will make the descriptor API can't be persisted in
>> Catalog
>> >> unless FLIP-80 is done.
>> >> 3) Schema#proctime and Schema#watermarkFor#boundedOutOfOrderTimestamps
>> >> The original intention behind these APIs are providing shortcut APIs
>> for
>> >> Table API users.
>> >> But I'm also fine to only provide the DDL-like methods if you have
>> >> concerns. We can discuss shortcuts in the future if users request.
>> >> 4) LikeOption
>> >> LikeOption.INCLUDING.ALL is a constant (enum values). I have added more
>> >> description about this in the FLIP.
>> >> 5) implementation?
>> >> I don't want to mention too much about implementation details in the
>> FLIP
>> >> at the beginning, because the API is already very long.
>> >> But I also added an "Implementation" section to explain them.
>> >> 6) static method vs new keyword
>> >> Personally I prefer the new keyword because it makes the API cleaner.
>> If we
>> >> want remove new keyword and use static methods, we have to:
>> >> Either adding a `Schema.builder()/create()` method as the starting
>> method,
>> >> Or duplicating all the methods as static methods, e.g. we have 12
>> methods
>> >> in `Kafka`, any of them can be a starting method, then we will have 24
>> >> methods in `Kafka`.
>> >> Both are not good, and it's hard to keep all the descriptors having the
>> >> same starting method name, but all the descriptors can start from the
>> same
>> >> new keyword.
>> >> Best,
>> >> Jark
>> >> On Thu, 9 Jul 2020 at 15:48, Dawid Wysakowicz <dwysakow...@apache.org>
>> >> wrote:
>> >>> Correction to my point 4. The example is correct. I did not read it
>> >>> carefully enough. Sorry for the confusion. Nevertheless I'd still like
>> >>> to see a bit more explanation on the LikeOptions.
>> >>>
>> >>> On 07/07/2020 04:32, Jark Wu wrote:
>> >>>> Hi everyone,
>> >>>>
>> >>>> Leonard and I prepared a FLIP about refactoring current Descriptor
>> API,
>> >>>> i.e. TableEnvironment#connect(). We would like to propose a new
>> >>> descriptor
>> >>>> API to register connectors in Table API.
>> >>>>
>> >>>> Since Flink 1.9, the community focused more on the new SQL DDL
>> feature.
>> >>>> After a series of releases, the SQL DDL is powerful and has many rich
>> >>>> features now. However, Descriptor API (the
>> `TableEnvironment#connect()`)
>> >>>> has been stagnant for a long time and missing lots of core features,
>> such
>> >>>> as computed columns and primary keys. That's frustrating for Table
>> API
>> >>>> users who want to register tables programmatically. Besides,
>> currently, a
>> >>>> connector must implement a corresponding Descriptor (e.g. `new
>> Kafka()`)
>> >>>> before using the "connect" API. Therefore, we hope to reduce this
>> effort
>> >>>> for connector developers, that custom source/sinks can be registered
>> via
>> >>>> the descriptor API without implementing a Descriptor.
>> >>>>
>> >>>> These are the problems we want to resolve in this FLIP. I'm looking
>> >>> forward
>> >>>> to your comments.
>> >>>>
>> >>>>
>> >>>
>> https://cwiki.apache.org/confluence/display/FLINK/FLIP-129%3A+Refactor+Descriptor+API+to+register+connector+for+Table+API
>> >>>>
>> >>>> Best,
>> >>>> Jark
>> >>>>
>> >>>
>> >>>
>> >
>>
>>
>
> --
> Best, Jingsong Lee
>
